HomeMy WebLinkAboutREPORT Soil 920 Big Thompson Ave 2020-02-14REPORT COVER PAGE
Geotechnical Engineering Report
__________________________________________________________________________
OLM New Rectory Building and Kitchen Addition
Estes Park, Colorado
February 14, 2020
Terracon Project No. 22195040
Prepared for:
Our Lady of the Mountains Catholic Church
Estes Park, Colorado
Prepared by:
Terracon Consultants, Inc.
1831 Lefthand Circle, Suite C
Longmont, Colorado 80501
Terracon Consultants, Inc. 1831 Lefthand Circle, Suite C Longmont, Colorado 80501
P (303) 776 3921 F (303) 776 4041 terracon.com
REPORT COVER LETTER TO SIGN
February 14, 2020
Our Lady of the Mountains Catholic Church
920 Big Thompson Avenue
Estes Park, Colorado 80517
Attn: Mr. Shawn Swisher – Business Manager
P:(970) 586 8111
E:shawn@olmestes.org
Re: Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition
920 Big Thompson Avenue
Estes Park, Colorado
Terracon Project No. 22195040
Mr. Swisher:
We have completed the Geotechnical Engineering services for the project referenced above. This
study was performed in general accordance with Terracon Proposal No. P22195040 dated
January 2, 2020. This report presents the findings of the subsurface exploration and provides
geotechnical recommendations concerning earthwork and the design and construction of
foundations, floor slabs and other earth-connected aspects for the proposed project.
We appreciate the opportunity to be of service to you on this project. If you have any questions
concerning this report, or if we may be of further service, please contact us.
Sincerely,
Terracon Consultants, Inc.
Eric S. Willis, P.E.Eric D. Bernhardt, P.E.
Senior Project Manager/Engineer Geotechnical Department Manager
2/14/2020
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REPORT TOPICS
REPORT TOPICS
REPORT SUMMARY ....................................................................................................... i
INTRODUCTION ............................................................................................................. 1
SITE CONDITIONS ......................................................................................................... 1
PROJECT DESCRIPTION .............................................................................................. 2
GEOTECHNICAL CHARACTERIZATION ...................................................................... 3
GEOTECHNICAL OVERVIEW ....................................................................................... 5
EARTHWORK................................................................................................................. 6
SHALLOW FOUNDATIONS ......................................................................................... 12
SEISMIC CONSIDERATIONS ...................................................................................... 17
FLOOR SLABS............................................................................................................. 17
RETAINING WALLS AND BELOW GRADE CONSTRUCTION .................................. 19
ADDITIONAL DESIGN AND CONSTRUCTION CONSIDERATIONS .......................... 22
GENERAL COMMENTS ............................................................................................... 23
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ATTACHMENTS
EXPLORATION AND TESTING PROCEDURES
SITE LOCATION AND EXPLORATION PLANS
EXPLORATION RESULTS (Boring Logs and Laboratory Data)
SUPPORTING INFORMATION (General Notes, Unified Soil Classification System and
Description of Rock Properties
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Responsive ■Resourceful ■Reliable i
REPORT SUMMARY
Topic 1 Overview Statement 2
Geotechnical
Characterization
Subsurface conditions encountered in the area of the rectory building consisted of
about 1½ to 2 feet of silty sand overlying metamorphic bedrock. Subsurface
conditions in the boring drilled in the kitchen addition area consisted of about 6½ feet
of existing sand fill overlying bedrock. No groundwater was observed in the test
borings during or shortly after completion of drilling to the depths explored.
Geotechnical
Overview
Based on geotechnical conditions encountered in our test borings, the site appears
suitable for the proposed construction from a geotechnical point of view provided
certain precautions and design and construction recommendations presented in the
report are followed. We have identified several geotechnical conditions that could
impact design, construction and performance of the structures and other site
improvements. These include existing fill (believed to be undocumented fill) in the
kitchen addition area and difficult excavation of the bedrock in the area of the
proposed rectory building. These conditions will require particular attention in project
planning, design and during construction and are discussed in greater detail in the
report.
Shallow
Foundations
Based on the field exploration and laboratory test results and the type of construction
planned, it is our opinion the proposed rectory building can be supported on shallow
spread footings bearing on undisturbed bedrock.
Approximately 6½ feet of existing sand fill (undocumented fill) was encountered in
the boring drilled in the area of the kitchen addition. Existing fill should not be relied
upon for foundation support and should be re-worked (over-excavated down to native
soil/bedrock, moisture conditioned and recompacted) or replaced with approved import
materials prior to foundation construction. Following the prescribed corrective work, we
believe the kitchen addition can be supported on spread footings bearing on properly
compacted engineered fill.
Floor Slabs
Based on our boring data, we anticipate non-expansive bedrock or possibly native
silty sand and/or properly compacted engineered fill will support the
basement/garage floor slab in the rectory building. These conditions are
considered suitable for support of conventional concrete slabs-on-grade.
Existing fill was encountered in the boring drilled in the area of the kitchen addition.
The fill will present a risk of settlement of floor slabs. To reduce risk of movement,
we recommend the existing fill be removed down to native soil/bedrock and reworked
or replaced prior to slab construction. Partial over-excavation and
recompaction/replacement of the fill below the slab could be considered provided
additional risk is acceptable. Another option to mitigate the impact of existing fill on
floor slab construction would be the use of a suspended floor (crawl space)
supported independent of the ground.
Earthwork Difficult excavation of the bedrock should be anticipated on this site. Excavation into
bedrock will likely require the use of large rippers, pneumatic hammers or other
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Responsive ■Resourceful ■Reliable ii
Topic 1 Overview Statement 2
specialized heavy-duty rock excavation equipment in order to advance excavations.
Drilling and blasting (if allowed) may also be required to advance excavations into
the bedrock.
On-site soils, properly processed bedrock materials or low volume change import
materials approved by Terracon can be used as fill/backfill material on the site
provided they are placed and compacted as described in the report. Bedrock
materials should be broken down and processed to a “soil-like” consistency. The
earthwork contractor should expect significant mechanical processing of the bedrock
materials will be needed to meet these requirements.
Surface drainage should be designed, constructed and maintained to provide rapid
removal of surface water runoff away from the proposed structures. Water should not
be allowed to pond adjacent to foundations or other site improvements and
conservative irrigation practices should be followed to avoid wetting of the subsurface
materials.
Basement
Construction
We understand the rectory building will be constructed with a walk-out level directed
to the south and west. Based on subsurface conditions encountered in our borings,
we believe basement construction can be used provided a perimeter drainage system
is installed.
1.If the reader is reviewing this report as a pdf, the topics above can be used to access the appropriate section
of the report by simply clicking on the topic itself.
2.This summary is for convenience only. It should be used in conjunction with the entire report for decision
making and design purposes. The section titled General Comments should be read for an understanding
of the limitations of this geotechnical engineering report.
3.Close monitoring of the construction operations and implementing drainage recommendations discussed in
this report will be important in achieving the intended foundation and slab performance. We therefore
recommend Terracon be retained to monitor this portion of the work.
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INTRODUCTION
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition
920 Big Thompson Avenue
Estes Park, Colorado
Terracon Project No. 22195040
February 14, 2020
INTRODUCTION
A geotechnical engineering report has been completed for the proposed rectory building and kitchen
addition to be located at 920 Big Thompson Avenue in Estes Park, Colorado. Two (2) borings,
designated TB-1 and TB-2 were performed in the area of the proposed rectory building and one (1)
boring, designated TB-3 was completed in the area of the kitchen addition. Borings were drilled to
depths of about 13 to 20 feet below existing ground surface. Maps showing the site and boring
locations are shown in the Site Location and Exploration Plan sections, respectively. Boring
logs and laboratory testing data are included in the Exploration Results section of this report.
The purpose of these services is to provide information and geotechnical engineering
recommendations relative to:
■Subsurface soil/bedrock conditions ■Floor slab design and construction
■Groundwater conditions ■Retaining walls
■Site preparation and earthwork ■Basement construction
■Foundation design and construction ■Surface drainage considerations
■Seismic site classification
The recommendations contained in this report are based on the results of field and laboratory
testing, engineering analyses, experience with similar soil/bedrock conditions and structures, and
our understanding of the proposed project.
SITE CONDITIONS
The following description of site conditions is derived from our site visits in association with the
field exploration and our review of publicly available geologic and topographic maps.
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
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Item Description
Location
The project is located at 920 Big Thompson Avenue in Estes Park, Colorado.
Specifically, the kitchen addition will be located at the southeast corner of the
existing church building, while the rectory building will be sited approximately
250 feet to the south and west of the church. The general location of the
project site is 40.3816° N 105.5082° W. See Site Location
Existing
Improvements/Existing
Site features
The project site consists of a developed church property in Estes Park,
Colorado. Big Thompson Avenue/HWY 34 borders the north side of the site,
while Vista Lane and Hillside Lane form the west and east boundaries of the
property, respectively. In general, residential and/or commercial/retail
development surrounds the project area.
The property is currently occupied by the existing Our Lady of the Mountains
Catholic Church facility. In general, the building is surrounded by existing
landscape features, concrete flatwork and asphalt paved parking areas and
drive lanes. The church building is a single to two-story structure with an
apparent walkout basement directed to the south. We assume the existing
church building is supported on spread footing foundations.
Current Ground Cover
The ground surface in the area of the proposed rectory building is covered
mostly with native weeds/grass along with scattered evergreen trees and
shrubs. Rock outcrops were noted in the generally vicinity of test boring TB-
1.
The ground surface in the area of the kitchen addition is covered with
weeds/grass, minor landscape features and concrete flatwork.
Existing Topography
Review of the topographic map provided indicates the ground surface in the
area of the proposed rectory building slopes moderately down to the south.
We measured a difference in elevation of about 12 feet across the location of
the borings drilled in the rectory building. Surface slopes in this area are
estimated to be on the order of about 5H:1V (horizontal to vertical), or less.
The area of the proposed kitchen addition is relatively level with a gentle
slope down to the south. In addition, an embankment fill slope is located to
the south of the kitchen addition and is estimated to be about 8 to 10 feet
high. The slope is estimated to be on the order of about 2H:1V (horizontal to
vertical), or steeper.
Water Features
Water features were not observed on or immediately adjacent to the project
site. However, the Big Thompson River and Estes Lake are located about
750 to 1,000 feet to the south and are situated topographically down-gradient.
PROJECT DESCRIPTION
Our initial understanding of the project was provided in our proposal and was discussed in the
project planning stage. A period of time/collaboration has transpired since the project was
initiated, and our final understanding of the project conditions is as follows:
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
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Item Description
Project Description
The project will include design and construction of a new rectory building along
with a small kitchen addition. The rectory building will have a footprint of about
2,600 square feet, while the kitchen addition will include about 900 square
feet. The rectory building will be single-story with a walkout basement level.
We understand the garage and mechanical room will be at the same level as
the basement. The balance of the rectory building footprint (northwest corner)
will include a crawl space. The kitchen addition will be single-story with a slab-
on-grade floor.
Building Construction
Information provided indicates both of the structures will consist of wood-
frame construction with some type of architectural veneer supported on
reinforced concrete foundation systems. We expect conventional concrete
slabs-on-grade are preferred for the interior floors, if subsurface conditions
permit.
Foundation/Floor
Loads
Foundation loads were not available at the time of the report. However,
considering the size and type of construction, we anticipate comparatively light
foundation loads. Based on our experience with similar projects, we assume
the following loads:
■Column/Point Loads: 30 to 60 kips (assumed)
■Wall/Line Loads: 1½ to 4 klf (assumed)
■Slab-On-Grade Floors: 150 psf maximum (assumed)
Grading
Final grading plans were not available at the time of the report. However, we
anticipate some site grading in the area of the new rectory building will be
needed for surface drainage and other development considerations.
Cut and Fill Slopes Assumed to be no steeper than 3H:1V (Horizontal to Vertical).
Below Grade
Areas/Retaining Walls
Partial basement in rectory building. We anticipate maximum basement
excavation depths up to about 10 to 12 feet may be required. Short retaining
walls may also be constructed to the west of the proposed rectory building.
Preliminary information indicates the walls will be on the order of about 2 to 4
feet tall.
GEOTECHNICAL CHARACTERIZATION
Subsurface Profile
The geotechnical characterization as described in the table and sections below forms the basis
of our geotechnical calculations and evaluation of site preparation, foundation and floor slab
construction. As noted in General Comments, the characterization is based upon widely spaced
exploration points across the site, and variations are always possible.
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
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Subsurface conditions at the boring locations can be generalized as follows:
Approximate
Depth to Bottom
of Stratum
Material Encountered
Consistency or
Relative Density/
Hardness
General Engineering
Properties
About 4 inches in
borings TB-1 and 2 Vegetative soil layer N/A N/A
About 1½ to 2 feet
in borings TB-1 and
2
Silty sand, trace gravel Not determined Non-plastic, judged to be non-
expansive
About 6½ feet in
boring TB-3
Existing Fill; Silty,
clayey sand with gravel Loose
Low plasticity, non-expansive,
low collapse potential, low to
moderate compressibility
Extended to bottom
of all borings
Biotite Schist
(Metamorphic Bedrock)
Weathered to very
hard
Judged to be essentially non-
expansive, moderate to high
load bearing capacity
Note: Test boring TB-1 (drilled in the area of the rectory building) encountered practical auger refusal
on very hard bedrock at a depth of about 13 feet below ground surface.
Conditions encountered at each boring location are indicated on the individual boring logs shown
in the Exploration Results section and are attached to this report. Stratification boundaries on
the boring logs represent the approximate location of changes in soil/bedrock types; in situ, the
transition between materials may be gradual.
Groundwater Conditions
The boreholes were observed while drilling and shortly after completion for the presence and level
of groundwater. In the interest of safety, the borings were backfilled prior to leaving the site and
therefore delayed groundwater measurements were not obtained. The water levels observed in
the boreholes can be found on the boring logs in Exploration Results and are summarized below.
Boring Number
Approximate Depth to
Groundwater During Drilling
(feet)1
Approximate Depth to
Groundwater ¼ to 3 Hours
After Drilling (feet)1
TB-1 None encountered Dry cave-in at 12
TB-2 None encountered Dry cave-in at 18½
TB-3 None encountered Dry at 19
1.Below ground surface
These observations represent short-term groundwater conditions at the time of and shortly after
the field exploration, and may not be indicative of other times, or at other locations.
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
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Zones of perched and/or trapped groundwater may occur at times in the subsurface soils
overlying bedrock, on top of the bedrock surface or within permeable fractures in the bedrock
materials. The location and amount of perched water is dependent upon several factors, including
hydrologic conditions, type of site development, irrigation demands on or adjacent to the site,
fluctuations in nearby water features, seasonal and weather conditions. The possibility of
development of perched water should be considered when developing the design and
construction plans for the project, particularly where below-grade/basement construction is
planned.
GEOTECHNICAL OVERVIEW
Based on geotechnical conditions encountered in our test borings, the site appears suitable for
the proposed construction from a geotechnical point of view provided certain precautions and
design and construction recommendations presented in this report are followed. We have
identified several geotechnical conditions that could impact design, construction and performance
of the structures and other site improvements. These include existing fill (believed to be
undocumented fill) in the area of the kitchen addition and difficult excavation of the bedrock in the
area of the proposed rectory building. These conditions will require particular attention in project
planning, design and during construction and are discussed in greater detail in the following
sections.
Existing Fill
Approximately 6½ feet of existing fill was encountered in the test boring (TB-3) drilled in the area
of the kitchen addition. Based on visual observation and existing topography, we anticipate fill
depths will likely decrease to the north and increase to the south. We are not aware whether the
existing fill was placed under the observation and testing of a geotechnical engineer. Therefore,
we consider the fill to be undocumented.
Undocumented fill can present a greater than normal risk of post-construction movement and
distress to shallow foundations, floor slabs and other at-grade improvements supported on or
above these materials. Consequently, it is our opinion the existing fill should not be relied upon for
support and should be re-worked (removed down to native soil/bedrock, moisture conditioned and
recompacted) or replaced with approved import materials prior to foundation and floor slab
construction.
Difficult Excavation
Metamorphic bedrock (Biotite Schist) is present at shallow depth (about 1½ to 2 feet below ground
surface) in the area of the proposed rectory building. In addition, resistant rock outcrops were
noted in the generally vicinity of test boring TB-1 located on the uphill side of the proposed rectory.
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Responsive ■Resourceful ■Reliable 6
With the exception of the upper part of the bedrock, penetration resistance measurements taken
in the bedrock were typically 2 inches or less by 50 blows from a 140-pound hammer falling 30
inches. In addition, practical auger refusal was encountered in boring TB-1 at a depth of about
13½ feet below the existing ground surface. Excavation into bedrock is anticipated to be difficult
and will require the use of large rippers, pneumatic hammers or other specialized heavy-duty rock
excavation equipment in order to advance excavations. Drilling and blasting (if allowed) may also
be required to advance excavations into the bedrock.
The means and methods for rock excavation should be evaluated and determined by the
excavation contractor. Consideration should be given to obtaining a unit price for difficult
excavation in the contract documents for the project. Furthermore, we recommend a contingency
be provided in the construction budget for difficult excavation.
EARTHWORK
The following presents recommendations for site preparation, excavation, subgrade preparation
and placement of engineered fills on the project. Recommendations include critical quality criteria
as necessary to render the site in the state considered in our geotechnical engineering evaluation
for foundations and floor slabs. Earthwork on the project should be observed and evaluated by
Terracon. The evaluation of earthwork should include observation and testing of existing fill
removal, placement of engineered fill, subgrade preparation, foundation bearing soils, and other
geotechnical conditions exposed during the construction of the project.
Site Preparation
Site preparation should commence with removal of existing vegetation, topsoil and any loose,
soft, or otherwise unsuitable material from the proposed construction areas. Pavements and/or
flatwork within the construction areas should be removed at this time as well. Stripped materials
consisting of vegetation and organic materials should be wasted from the site or used to re-
vegetate landscaped areas or exposed slopes after completion of earthwork operations.
Existing (undocumented) fill is present in the area of the proposed kitchen addition. These
materials should not be relied upon for support and should be treated as described in other
sections of the report. Terracon should be contacted to observe the fill removal process to more
accurately define the depth of the fill layer.
Although evidence of underground facilities was not observed in the areas of proposed
construction, such features could be encountered during construction. If unexpected fills or
underground facilities are encountered, such features should be removed, and the excavation
thoroughly cleaned. Terracon should observe the excavation prior to backfill placement and/or
construction.
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Responsive ■Resourceful ■Reliable 7
Where new fill is placed on existing slopes steeper than 5H:1V, benches should be cut into the
existing slopes prior to fill placement. Benches should have a minimum vertical face height of 2
feet and a maximum vertical face height of 5 feet and should be cut wide enough to accommodate
compaction equipment. Benches should be sloped at about 2 percent towards the slope face.
This benching will help provide a positive bond between the fill and existing soil/bedrock and
reduce the possibility of failure along the fill/soil or bedrock interface.
Exposed surfaces should be free of mounds and depressions that could prevent uniform
compaction. Following completion of stripping and rough grading but prior to placement of new
fill, the exposed ground should be scarified, moisture conditioned as needed and re-compacted.
The subgrade should then be proof-rolled to help delineate weak or disturbed areas at or near
the ground surface. Unsuitable areas should be improved by moisture adjustment and compaction
or by undercutting and placement of suitable compacted fill.
Fill Material Types
On-site soils free of vegetation, organic matter and other unsuitable materials, properly processed
bedrock materials or low volume change import materials approved by Terracon may be used as
fill/backfill material on the site. Bedrock materials should be broken down and processed to a
“soil-like” consistency, with no particles greater than about 4 inches in size. The earthwork
contractor should expect significant mechanical processing of the bedrock materials will be
needed to meet these requirements.
In general, imported materials meeting the properties presented below should be acceptable for
use on the site. However, imported soils should be evaluated and approved by the geotechnical
engineer prior to delivery to the site.
Gradation/Property Percent Finer by Weight
(ASTM D422/C136)
3-inch 100
No. 4 Sieve 30 to 100
No. 50 Sieve 10 to 60
No. 200 Sieve 5 to 20
■Liquid Limit (LL)30 (max.)
■Plasticity Index (PI)6 (max.)
Other import fill material types may be suitable for use on the site depending upon proposed
application and location on the site and could be tested and approved for use on a case-by-case
basis.
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
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Fill Compaction Requirements
Structural and general fill/backfill should meet the following compaction requirements.
Item Description
Fill Lift Thickness
■9 to 12-inches or less in loose thickness when
heavy, self-propelled compaction equipment is
used
■4 to 6 inches in loose thickness when hand-
guided equipment (i.e. jumping jack or plate
compactor) is used
Compaction Requirements1
■At least 95% of ASTM D698 (for fill/backfill
depth ≤ 8 feet)
■At least 98% of ASTM D698 (for portion of
fill/backfill ˃ 8 feet)
Moisture Content On-Site/Import Sands or
Properly Processed Bedrock Materials2
-2 to +2% of the optimum moisture content as
determined by the standard Proctor test
1.Engineered fill should be placed and compacted in horizontal lifts, using equipment and procedures that
will produce recommended moisture contents and densities throughout the lift. A construction disc or other
suitable processing equipment will be needed to thoroughly process the materials and to aid in achieving
uniform moisture content throughout the fill.
2.The contractor should expect some moisture adjustment and processing of the site soil/bedrock or import
materials will be needed prior to or during compaction operations.
3.Care should be taken during the fill placement process to avoid zones of dissimilar fill. Improvements
constructed over varying fill types are at a higher risk of differential movement compared to improvements
over a uniform fill zone. We support the use of a single import source to avoid this condition.
Slopes
For new slopes in compacted fill or cut areas where saturation of the slopes will not occur, we
suggest slopes of 3H:1V (horizontal to vertical), or less. Use of flatter slopes of 4H:1V (horizontal
to vertical) is preferable to reduce erosion and maintenance problems. Some local raveling and/or
surface sloughing may occur on constructed slopes until vegetation is re-established. If saturated
or steeper slopes and/or slopes over about 10 feet in height are anticipated, or if structures or
other surcharge loads will be located within a distance of the slope height from the crest of the
slope, the slopes should be evaluated for stability on an individual basis.
The face of all slopes should be compacted to the minimum specifications described above.
Ideally, fill slopes should be over-built and then cut back to the final configuration to develop and
adequately compacted slope face. Slopes should be revegetated as soon as possible to reduce
the potential for erosion problems. Seeded slopes should be protected with erosion mats until the
vegetation is established. Surface drainage is critical to performance of slopes and should be
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Responsive ■Resourceful ■Reliable 9
designed, constructed and maintained to direct water away from slope faces and to prevent ponding
adjacent to the crest or toe of the slope.
Excavation and Utility Trench Construction
We anticipate excavations up to about 10 to 12 feet may be necessary for construction of the
rectory building. We believe the near surface soils and existing fill encountered in our exploratory
borings can be excavated with conventional excavation equipment. Excavation into bedrock is
anticipated to be difficult and will likely require the use of large rippers, pneumatic hammers or
other specialized heavy-duty rock excavation equipment in order to advance excavations. Drilling
and blasting (if allowed) may also be required to advance excavations into the bedrock. The
means and methods for rock excavation should be evaluated and determined by the excavation
contractor. Consideration should be given to obtaining a unit price for difficult excavation in the
contract documents for the project. Furthermore, we recommend a contingency be provided in
the construction budget for difficult excavation.
Groundwater seepage is not expected for planned excavations on the site. However, if seepage
occurs or rain or snow-melt water develops in the excavation, it should be removed as soon as
possible.
Trench excavations should be made with sufficient working space to permit construction including
backfill placement and compaction. Trench backfill should consist of the on-site soil, properly
processed bedrock materials or approved imported materials. Trench backfill should be placed
and compacted as described under Fill Compaction Requirements. It is strongly recommended
a representative of the geotechnical engineer provide full-time observation and compaction
testing of trench backfill within building areas.
Underground piping within or near the proposed structures should be designed and constructed
to accommodate movement so deviations in alignment do not result in breakage or distress. Utility
knockouts in foundation walls/grade beams should be oversized to accommodate differential
movements.
The individual contractor(s) is responsible for designing and constructing stable, temporary
excavations in order to maintain stability of excavation sides and bottom as well as any adjacent
structures, foundations and utilities. Care should be taken during construction to avoid affecting
existing foundations. Excavations for the project should not undermine existing foundations.
These conditions may require shoring of excavations or underpinning of existing foundations to
protect the structural integrity of the existing building. Excavations should be sloped or shored in
the interest of safety following local and federal regulations, including current Occupational Safety
and Health Administration (OSHA) excavation and trench safety standards. As a safety measure,
it is suggested vehicles and soil piles be kept to a minimum lateral distance from the crest of the
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
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slope equal to no less than the slope height. Exposed slope faces should be protected against
the elements.
The soils to be penetrated by the proposed excavations may vary significantly across the site.
The preliminary soil classifications are based solely on the materials encountered in the borings
drilled at the indicated locations. The contractor should verify similar conditions exist throughout
the proposed area of excavation. If different subsurface conditions are encountered at the time of
construction, the actual conditions should be evaluated to determine any excavation modifications
necessary to maintain safe conditions.
Grading and Drainage
Proper drainage and surface water management is important to the performance of foundations,
floor slabs, basement areas and other site improvements. The following recommendations are
considered good practice for any site and should be implemented where applicable and/or to the
extent possible.
Grades must be adjusted to provide positive drainage away from the buildings and other site
improvements during construction and maintained throughout the life of the proposed facility.
Infiltration of water into utility or foundation excavations must be prevented during construction.
Landscaped irrigation adjacent to the foundation system should be minimized. Plants placed close
to foundation walls should be limited to those with low moisture requirements. The importance of
proper irrigation practices cannot be over emphasized. Irrigation should be limited to the minimum
amount needed to maintain vegetation; application of more water will increase likelihood of soil
movements.
We recommend constructed slopes of about 6 inches in the first 10 feet (5 percent slope) in
landscaped areas around the building, where practical. Locally, flatter grades may be necessary
to transition ADA access requirements for flatwork. The ground surface should be sloped in such
a manner that water will not pond between or adjacent to structures and other site improvements.
Concrete curbs and sidewalks may “dam” surface runoff adjacent to the buildings and disrupt
proper flow. Use of “chase” drains or weep holes at low points in the curb should be considered
to promote proper drainage.
Backfill against foundations, exterior walls and in utility and sprinkler line trenches should be well
compacted and free of construction debris to reduce moisture infiltration. Some settlement of wall
backfill should be expected even if properly compacted. Areas where backfill has settled should
be repaired and re-graded immediately to maintain proper slope away from the foundation.
Flatwork and pavements will be subject to post construction movement. Maximum grades
practical should be used for paving and flatwork to prevent areas where water can pond. Where
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paving or flatwork abuts the structure, care should be taken that joints are properly sealed and
maintained to prevent the infiltration of surface water.
Planters located adjacent to the structure should be self-contained. Sprinkler mains and spray
heads should not be installed or allowed to discharge within 5 feet of foundation walls. Roof drains
should discharge beyond the limits of backfill zones or into appropriate storm sewer or detention
areas. Downspout extensions and splash blocks should be provided at all discharge points. Roof
drains can also be connected to buried, solid pipe outlets. Downspouts, extensions and drain
outlets should be monitored and maintained.
Water permitted to pond near or adjacent to the perimeter of the structures (either during or post-
construction) can result in higher soil movements than those discussed in this report. As a result,
estimations of potential movement described in this report cannot be relied upon if positive
drainage is not obtained and maintained, and water is allowed to infiltrate the fill and/or subgrade.
After building construction and prior to project completion, we recommend verification of final
grading be performed to document that positive drainage, as described in this section, has been
achieved. Maintenance of surface drainage is imperative subsequent to construction and
becomes the responsibility of the owner.
Earthwork Construction Considerations
The near surface soils found on this site are anticipated to be relatively stable and are not
expected to “pump” or deform excessively upon initial exposure. However, the site soils can lose
strength when elevated in moisture content. In addition, overall stability of the subgrade can be
affected by precipitation, excessive compaction water, repetitive construction traffic, or other
factors. Consequently, subgrade “pumping” and unstable soil conditions could develop during
earthwork operations or other construction activities.
If unstable or soft/loose ground conditions develop during earthwork or other construction
activities, some method of soil improvement or stabilization will be needed prior to fill placement
and/or foundation of floor slab construction. Prior to placing fill or structures on soft, yielding
subgrade, we recommend stabilization by either moisture adjustment and recompaction,
undercutting weak areas and replacement with select granular fill and/or geogrid, or by placing a
layer of angular rock and crowding it into the subgrade until a firm base is obtained. In any event,
we feel the appropriate method and level of stabilization (if any) should be evaluated and can best
be determined on a case-by-case basis during construction once the entire subgrade and overall
conditions are exposed.
The subgrade should be evaluated by a Terracon representative upon completion of filling
operations. Once fill is placed and the subgrade is prepared, it is important measures be planned
and taken to reduce drying of the near surface materials. If the fill dries excessively prior to
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foundation, floor slab or flatwork construction, then it will be necessary to rework the upper, drier
materials just prior to construction. Likewise, completed subgrades that have become saturated,
frozen, disturbed or altered by construction activity should be restored to the conditions
recommended in this report.
Construction site safety is the sole responsibility of the contractor who controls the means,
methods, and sequencing of construction operations. Under no circumstances shall the
information provided herein be interpreted to mean Terracon is assuming responsibility for
construction site safety, or the contractor's activities; such responsibility shall neither be implied
nor inferred.
Construction Observation and Testing
The earthwork efforts should be monitored under the guidance of Terracon. Monitoring should
include documentation of adequate removal of vegetation and top soil and existing fill materials.
Each lift of compacted fill/backfill should be tested, evaluated, and reworked as necessary until
approved by the Geotechnical Engineer prior to placement of additional lifts.
In areas of foundation excavations, the bearing subgrade should be evaluated under the guidance
of Terracon. In the event unanticipated conditions are encountered, we should prescribe
mitigation options.
In addition to the documentation of the essential parameters necessary for construction, the
continuation of Terracon into the construction phase of the project provides the continuity to
maintain our evaluation of subsurface conditions, including assessing variations and associated
design changes.
SHALLOW FOUNDATIONS
RECTORY BUILDING
Subsurface conditions in the area of the rectory building generally consist of about 1½ to 2 feet
of silty sand overlying weathered to very hard bedrock. Considering the size and type of
construction planned for the rectory and the subsurface conditions encountered in our test
borings, we believe spread footings bearing on undisturbed bedrock materials can be used for
support of the proposed building. Design and construction recommendations for shallow
foundations for the proposed structure are presented in the following table and paragraphs.
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If the site has been prepared in accordance with the requirements noted in Earthwork and other
appropriate sections of the report, the following design parameters are applicable for shallow
spread footings.
Spread Footing Design Recommendations (Rectory Building)
Item Description
Bearing Material Undisturbed bedrock
Maximum Allowable Soil Bearing Pressure 1 4,000 psf
Minimum Embedment Below Finished Grade
for Frost Protection 2 36 inches
Estimated Post-Construction Movement
Based on Assumed Structural Loads 3 1 inch, or less
Ultimate Passive Pressure 4 375 psf/ft
Ultimate Coefficient of Sliding Friction
(footings on bedrock)4 0.60 times the vertical dead load
1.The allowable soil bearing pressure applies to dead loads plus design live load conditions and is the
maximum pressure that should be transmitted to the bearing soils in excess of the minimum surrounding
overburden pressure at the footing base elevation. Assumes soft/loose soils or disturbed bedrock materials,
if encountered, will be removed prior to placement of foundations.
2.For perimeter footings and footings beneath unheated areas. Interior column pads in heated areas should
bear at least 12 inches below the adjacent grade (or the top of the floor slab) for confinement of the bearing
materials and to develop the recommended bearing pressure.
3.Additional foundation movements could occur if surface water infiltrates the foundation soils; therefore,
proper drainage away from the foundation system should be provided in the final design, during construction
and maintained throughout the life of the structure. The sides of the excavation for spread footings must be
nearly vertical and the concrete should be placed neat against these vertical faces or backfill must be
compacted to at least 95 percent of the standard Proctor maximum dry density for the passive earth
pressure value to be valid. Passive pressure requires movement to generate the resistance and should
only be used when movement is tolerable, and the soil is well compacted and will not be removed. The
passive resistance and friction factor are ultimate values. As such, appropriate factors of safety should be
applied.
Footings should be proportioned to reduce differential foundation movement. Proportioning on
the basis of relative constant dead-load pressure can provide a means to reduce differential
movement between adjacent footings. Footings and foundation walls should be detailed and
reinforced as necessary to reduce the potential for distress caused by differential foundation
movement.
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Spread Footing Construction Considerations (Rectory Building)
Where bedrock is loosened during excavation or in the forming process for footings, or if otherwise
unsuitable bearing conditions are present, these materials should be removed prior to placement
of foundation concrete. Concrete should be placed soon after excavating to reduce bearing
material disturbance.
As noted in Earthwork, completed foundation excavations should be observed and evaluated by
a representative of Terracon well in advance of forming footings and placement of reinforcing
steel to confirm satisfactory bearing materials are present and subsurface conditions are
consistent with those encountered in our borings. If the soil conditions encountered differ
significantly from those presented in this report, supplemental recommendations will be required.
KITCHEN ADDITION
Subsurface conditions in the area of the kitchen addition generally consist of about 6½ feet of
existing sand fill (undocumented fill) overlying weathered to very hard bedrock. Depth of fill may
vary across the footprint of the proposed addition. As discussed previously, existing fill should not
be relied upon for support and should be re-worked (over-excavated down to native soil/bedrock,
moisture conditioned and recompacted) or replaced with approved import materials prior to
foundation construction. Over-excavation should also extend laterally beyond edges of the footing
at least 12 inches for each foot of over-excavation depth below the footing base elevation.
Considering the size and type of construction planned for the kitchen addition and the subsurface
conditions encountered in our test borings, we believe spread footings bearing on newly placed
engineered fill can be used for support of the proposed addition. Design and construction
recommendations for shallow foundations for the proposed addition are presented in the following
table and paragraphs.
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Spread Footing Design Recommendations (Kitchen Addition)
Item Description
Bearing Material Newly placed engineered fill extended to native soil/
bedrock
Maximum Allowable Soil Bearing Pressure 1 2,000 psf
Minimum Dimensions Isolated Column Strip Footing
24 inches 16 inches
Minimum Embedment Below Finished Grade
for Frost Protection 2 36 inches
Estimated Post-Construction Movement
Based on Assumed Structural Loads 3 About 1 inch
Ultimate Passive Pressure 4 375 psf/ft
Ultimate Coefficient of Sliding Friction
(footings on compacted sand fill)4 0.40 times the vertical dead load
1.The allowable soil bearing pressure applies to dead loads plus design live load conditions and is the
maximum pressure that should be transmitted to the bearing soils in excess of the minimum surrounding
overburden pressure at the footing base elevation. Assumes soft/loose soils, poorly compacted fill or
otherwise unsuitable bearing materials, if encountered, will be undercut and replaced with properly
compacted engineered fill.
2.For perimeter footings and footings beneath unheated areas. Interior column pads in heated areas should
bear at least 12 inches below the adjacent grade (or the top of the floor slab) for confinement of the bearing
materials and to develop the recommended bearing pressure.
3.Additional foundation movements could occur if surface water infiltrates the foundation soils; therefore,
proper drainage away from the foundation system should be provided in the final design, during construction
and maintained throughout the life of the structure. The sides of the excavation for spread footings must be
nearly vertical and the concrete should be placed neat against these vertical faces or backfill must be
compacted to at least 95 percent of the standard Proctor maximum dry density for the passive earth
pressure value to be valid. Passive pressure requires movement to generate the resistance and should
only be used when movement is tolerable, and the soil is well compacted and will not be removed. The
passive resistance and friction factor are ultimate values. As such, appropriate factors of safety should be
applied.
Differential movement between the addition and the existing building is expected to approach the
magnitude of the total movement of the addition. Ideally, expansion joints should be provided
between the existing building and the proposed addition to accommodate differential movements
between the two structures. Underground piping between the two structures should be designed
with flexible couplings and utility knockouts in foundation walls should be oversized, so minor
deflections in alignment do not result in breakage or distress.
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New footings should bear at or near the bearing elevation of immediately adjacent existing
foundations. Depending upon their locations and current loads on the existing footings, footings
for the new addition could cause settlement of adjacent foundations. To reduce this concern and
risk, clear distances at least equal to the new footing widths should be maintained between the
addition’s footings and footings supporting the existing building.
Footings should be proportioned to reduce differential foundation movement. Proportioning on
the basis of relative constant dead-load pressure can provide a means to reduce differential
movement between adjacent footings. Footings and foundation walls should be detailed and
reinforced as necessary to reduce the potential for distress caused by differential foundation
movement.
Spread Footing Construction Considerations (Kitchen Addition)
Care should be used while excavating adjacent to existing foundations of the building to avoid
undermining or otherwise disturbing these foundation elements. Excavations should not extend
into the stress influence zone of existing foundations unless they are underpinned or braced. The
stress influence zone is generally defined as the area below a line projected down at a 1H:1V
slope from the bottom edge of the existing foundation. If excavations need to extend below the
depth of existing foundations, we should be contacted to evaluate conditions and provide
additional recommendations, if needed. Also, when compacting within 10 feet of the existing
structure, a lightweight compactor should be used and backfill should be placed and compacted in
4 to 6-inch loose lifts.
An embankment fill slope is located to the south of the kitchen addition and is estimated to be
about 8 to 10 feet high. For foundations adjacent to slopes, a minimum horizontal setback of five
(5) feet should be maintained between the foundation base and slope face. In addition, the
setback should be at a location where an imaginary line extending downward at 45 degrees from
the nearest edge of the foundation does not intersect the slope face.
Where soils are loosened during excavation or in the forming process for footings, or if loose or
otherwise unsuitable bearing conditions are present, they should be removed to minimum depths
determined by the geotechnical engineer and replaced with approved engineered fill. Concrete
should be placed soon after excavating to reduce bearing material disturbance.
As noted in Earthwork, completed foundation excavations should be observed and evaluated by
a representative of Terracon well in advance of forming footings and placement of reinforcing
steel to confirm satisfactory bearing materials are present and subsurface conditions are
consistent with those encountered in our borings. If the soil conditions encountered differ
significantly from those presented in this report, supplemental recommendations will be required.
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SEISMIC CONSIDERATIONS
The seismic design requirements for buildings and other structures are based on Seismic Design
Category. Site Classification is required to determine the Seismic Design Category for a structure.
The Site Classification is based on the upper 100 feet of the site profile defined by a weighted
average value of either shear wave velocity, standard penetration resistance, or undrained shear
strength in accordance with Section 20.4 of ASCE 7 and the International Building Code (IBC).
Based on the soil/bedrock properties encountered at the site and as described on the exploration
logs and results, it is our professional opinion that the Seismic Site Classification is C.
Subsurface explorations at this site were extended to a maximum depth of about 20 feet. The site
properties below the maximum boring depth to 100 feet were estimated based on our experience
and knowledge of geologic conditions of the general area.
FLOOR SLABS
Existing fill was encountered in the boring drilled in the area of the kitchen addition. The fill will
present a risk of settlement of floor slabs constructed on or above these materials. To reduce risk
of movement and enhance floor slab performance, we recommend the existing fill be removed
down to native soil/bedrock and reworked or replaced prior to slab construction. Partial over-
excavation and recompaction/replacement of at least 3 feet of the fill below the slab could be
considered provided additional risk is acceptable. Another option to mitigate the impact of existing
fill on floor slab construction would be the use of a suspended floor (crawl space) supported
independent of the ground.
Based on our boring data, we anticipate non-expansive bedrock or possibly native silty sand
and/or properly compacted engineered fill will support the basement/garage floor slab in the
rectory building. Conventional concrete slabs-on-grade are normally used for these conditions
and typically perform well.
All slabs-on-grade undergo some movement. We believe risk of movement is low for the
soil/bedrock conditions encountered on this site and estimate settlement/heave of slabs-on-grade
constructed on undisturbed bedrock or properly compacted engineered fill and prepared subgrade
on the order of 1 inch, or less.
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Floor Slab Design Recommendations
Item Description
Floor Slab Support Properly compacted engineered fill, moisture conditioned
and compacted subgrade or undisturbed bedrock.
Slab Thickness
Slab reinforcement and thickness should be designed by
a qualified engineer based on actual loads imposed and
on intended slab use.
We recommend the following precautions be observed where slabs-on-grade are used. These
precautions will not eliminate slab movement. Rather, they tend to reduce damage when
movement occurs. Additional floor slab design and construction recommendations are as follows:
■Positive separations and/or isolation joints should be provided between slabs and
foundations, columns or utility lines to allow free vertical movement. This detail can reduce
cracking when movement of the slab occurs. Non-bearing partition walls placed on the
floor slab (if any) should be designed and constructed to allow some slab movement.
■Plumbing and utilities that pass-through slabs should be isolated from the slab and
constructed with flexible couplings. Utilities, as well as electrical and mechanical
equipment, should be constructed with sufficient flexibility to allow for movement.
■Frequent control joints should be provided in slabs to control the location and extent of
cracking in accordance with the American Concrete Institute (ACI). For additional
recommendations refer to the ACI Design Manual.
■The use of a vapor retarder should be considered beneath concrete slabs on grade that
will be covered with wood, tile, carpet or other moisture sensitive or impervious coverings,
or when the slab will support equipment sensitive to moisture. When conditions warrant
the use of a vapor retarder/barrier, the slab designer should refer to ACI 302 and/or ACI
360 for procedures and cautions regarding the use and placement of a vapor
retarder/barrier.
■Other design and construction considerations, as outlined in the ACI Design Manual,
Section 302.1R are recommended.
Floor Slab Construction Considerations
Fill/backfill placed beneath slabs and next to foundation walls/grade beams should be moisture
conditioned and compacted as described in the Earthwork section of this report. Soils loosened
during excavation or other construction activities should be removed or recompacted as described
in this report. Floor slabs should not be constructed on frozen subgrade.
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Once fill is placed and the floor slab subgrade is prepared, it is important measures be planned
and taken to reduce drying of the near surface materials. If the fill dries excessively prior to
building construction, then it will be necessary to rework the upper, drier materials just prior to
installing floor slabs.
We recommend the area underlying the floor slab be evaluated shortly before slab construction.
Particular attention should be paid to foundation wall backfill and areas where backfilled trenches
are located. Areas where unsuitable conditions are located should be repaired by removing and
replacing the affected material with properly compacted fill.
RETAINING WALLS AND BELOW GRADE CONSTRUCTION
We understand short retaining walls may also be constructed to the west of the proposed rectory
building. Preliminary information indicates the walls will be on the order of about 2 to 4 feet tall.
Furthermore, we assume the retaining walls will likely consist of cast-in-place (CIP) reinforced
concrete construction.
Retaining walls can be constructed on footing foundations designed for a maximum allowable soil
pressure of 2,000 pounds per square foot (psf) when bearing on native sand soils or properly
compacted engineered fill. Retaining wall foundations bearing entirely on undisturbed bedrock
may be designed for a soil pressure of 4,000 psf. Footings should have a minimum width of 18
inches and frost cover of at least 3 feet. The footings should be reinforced to help withstand
differential movements.
Lateral Earth Pressures
Reinforced concrete retaining walls and foundation walls with unbalanced backfill levels on
opposite sides should be designed for lateral earth pressures imposed by the soil backfill. Earth
pressures will be influenced by structural design of the walls, conditions of wall restraint, slope of
the backfill surface and type, compaction and drainage of the backfill. For purposes of design, we
have assumed backfill will consist of the on-site soils, properly processed bedrock materials or
approved import soil. If different type of backfill is used or other retaining wall systems (such as
MSE walls) are planned, we should be contacted to provide additional recommendations.
Active earth pressure is commonly used for design of walls that allow some wall rotation and
deflection. For walls that can deflect and rotate about the base, with top lateral movements of
about ½ to 1 percent of the wall height, lower “active” earth pressures could be considered for
design. For restrained walls where negligible or very little rotation and deflection will occur (such
as basement foundation walls), "at-rest" lateral earth pressures should be used in the design.
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Reinforced concrete walls should be designed for lateral earth pressures at least equal to those
indicated in the following table.
Earth Pressure
Conditions Backfill Soil Type Equivalent Fluid Density (pcf)
Active (Ka)On-site sand soil or processed
bedrock 40
At-Rest (Ko)On-site sand soil or processed
bedrock 60
Passive (Kp)On-site sand soil or processed
bedrock 375
Passive earth pressure and frictional resistance can be used to resist sliding and overturning.
Passive resistance requires movement to generate the resistance. Passive resistance should only
be used when movement is tolerable, and the soil is well compacted and will not be removed. A
value of 0.40 can be used as the ultimate coefficient of friction between concrete and the native sand
soil or engineered fill. A value of 0.60 can be used between concrete and undisturbed bedrock.
The equivalent fluid densities and coefficient of friction presented above do not include a factor of
safety. As such, appropriate factors of safety should be applied to these values. Furthermore, the
equivalent fluid densities do not include allowances for hydrostatic pressures, surcharge loading,
and sloping backfill.
Retaining Wall Drainage
Free-draining granular backfill should be used behind retaining walls to help relieve hydrostatic
pressure and provide drainage. We recommend a free-draining gravel material with less than 5
percent fines (material passing the No. 200 sieve) be used for a zone within at least 1-foot behind
the walls. The gravel zone behind the wall and wall backfill should be placed in thin, loose lifts
and compacted. Heavy equipment should not operate within a distance closer than the exposed
height of retaining walls to prevent lateral pressures more than those provided. Special
precautions (e.g. bracing) should be taken to avoid over-stressing the walls during compaction.
We recommend weep holes and/or installation of a drain pipe at the base of the free-draining
backfill zone. If a drain is installed, it should consist of a minimum 4-inch perforated rigid PVC
pipe encased in free-draining gravel. The drain pipe should slope at least ½ percent to a positive
gravity outlet at either or both ends of the wall or be connected to outfall more than 5 feet in front
of the wall.
As an alternative, a prefabricated drainage structure may be used as a substitute for the granular
backfill adjacent to the retaining wall. A pre-fabricated drainage structure is a plastic drainage
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core or mesh which is covered with filter fabric to prevent soil intrusion and is fastened to the wall
prior to placing backfill. Prefabricated drainage should be installed following the manufacturer’s
recommendations.
Where the backfill zone is not covered with pavement or flatwork, we recommend the backfill zone
be capped with relatively impermeable soil to reduce infiltration and conveyance of surface water
through the wall backfill. In addition, surface drainage should be designed to direct water away from
the wall and to prevent ponding adjacent to the wall.
Basement Construction and Subsurface Drainage
We understand the rectory building will be constructed with a walk-out level directed to the south
and west. Our experience indicates surface water from precipitation, snowmelt and site irrigation
frequently flows through relatively permeable backfill adjacent to the building and collects on the
surface of less permeable soil/bedrock occurring at the bottom of the excavation. To reduce the
likelihood water pressure will develop outside foundation walls and the risk of accumulation of
water at the basement floor level, installation of a perimeter drainage system is recommended.
The drain trench and pipe should be constructed around the perimeter of the basement foundation
and sloped at a minimum 1 percent (⅛” drop per foot of drain) to a suitable outlet, such as a
positive gravity outfall or to a sump where water can be removed by pumping.
The drainage system should consist of a minimum 4-inch diameter rigid perforated pipe, encased
in free-draining gravel, placed in a trench at least 12-inches in width. The trench should be
excavated at a 1H:1V slope beginning at the bottom edge of the footing. The trench should not
be cut vertically at the edge of the footing.
The invert of the drain pipe, at its high-point, should be placed at least 2-inches below the bottom
of the footing. Gravel should encase the pipe and extend laterally to the edge of the footing. Gravel
should extend at least 6-inches above the drain pipe. The system should be underlain with a
polyethylene moisture barrier, sealed to the foundation wall and extended at least to the edge of
the backfill zone. The drain gravel should be covered with a non-woven geotextile fabric (or other
engineer approved material) and should cover the entire width of the gravel prior to placement of
backfill.
Crawl Space Construction
We understand the rectory building will include a crawl space area in the northwest corner of the
building footprint. Experience indicates over a period of time, moist conditions and possibly standing
water can develop in crawl space areas, particularly if proper surface drainage away from the
building is not provided and maintained or if over-watering of lawns and other landscape plantings
adjacent to the foundation occurs.
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As a precautionary measure, the provision of a drain should be considered for proposed crawl space
areas. The crawl space drain could be as simple as a shallow trench sloped to a suitable outlet or
could be a more elaborate system using perforated drain pipe embedded in free-draining gravel.
We are available to discuss this in greater detail upon request.
Crawl space areas should be well ventilated for indoor air quality to help manage humidity and to
facilitate moisture release. To help promote drainage towards the perimeter of the structure, we
recommend “crowning” the subgrade at the center of the crawl space area. To further manage
humidity, we believe best current practices involve placing a vapor retarder (10 mil polyethylene
membrane material, or equivalent) on the exposed soil in the crawl space. The vapor retarder
should be sealed at joints and attached to concrete foundation walls and other elements.
ADDITIONAL DESIGN AND CONSTRUCTION CONSIDERATIONS
Soluble Sulfates Test Results (Concrete)
Soluble sulfate concentrations were measured for samples of the soil/bedrock that will likely be in
contact with project concrete. The sulfate concentrations measured in the samples varied from
0.001 to 0.002 percent. Sulfate concentrations of less than 0.1 percent indicate Class 0 exposure
to sulfate attack for concrete in contact with the subsoils, according to the American Concrete
Institute (ACI)Guide to Durable Concrete. For this level of sulfate concentrations, ACI indicates
any type of cement can be used for concrete in contact with the subsoils/bedrock.
Therefore, Type I Portland cement should be suitable for concrete on and below grade. However,
if there is no, or minimal cost differential, use of Type II Portland cement (or equivalent) should
be considered for additional sulfate resistance of construction concrete. Foundation concrete
should be designed in accordance with the provisions of the ACI Design Manual, Section 318,
Chapter 4.
Exterior Slabs/Flatwork
We anticipate exterior slabs/flatwork will be supported on essentially non-expansive soil/bedrock
or on properly compacted engineered fill. Sidewalks and other flatwork are normally constructed
as slabs-on-grade where these conditions are present. Performance of flatwork supported on the
site soil/bedrock or engineered fill can be erratic and these features may heave/settle to some
degree and crack when the underlying soils become elevated in moisture content or due to frost
heave. Exterior slabs can be affected on all sites.
In addition, compacted backfill or existing soils may swell/compress or foundation wall backfill
may consolidate with increasing moisture content; therefore, exterior slabs could heave or settle,
resulting in cracking or vertical offsets. It is generally not feasible to eliminate the potential for
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movement of exterior flatwork. The potential for damage would be greatest where exterior slabs
are constructed adjacent to the buildings or other structural elements. To reduce the potential for
damage, we recommend:
■Exterior slabs be supported on carefully processed and moisture conditioned fill/subgrade
■Strict moisture-density control during placement of fill/backfills
■Placement of effective control joints on relatively close centers and isolation joints between
slabs and other structural elements
■Provision for adequate drainage in areas adjoining the slabs
■Use of designs which allow free vertical movement between the exterior slabs and
adjoining structural elements
In those locations where movement of exterior slabs must be reduced or where there is low
tolerance for movement (such as at building doors), consideration should be given to structurally
supporting exterior flatwork on haunches.
GENERAL COMMENTS
As the project progresses, we address assumptions by incorporating information provided by the
design team, if any. Revised project information that reflects actual conditions important to our
services is reflected in the final report. The design team should collaborate with Terracon to
confirm these assumptions and to prepare the final design plans and specifications. This facilitates
the incorporation of our opinions related to implementation of our geotechnical recommendations.
Any information conveyed prior to the final report is for informational purposes only and should
not be considered or used for decision-making purposes.
Our analysis and opinions are based upon our understanding of the project, the geotechnical
conditions in the area, and the data obtained from our site exploration. Natural variations will occur
between exploration point locations or due to the modifying effects of construction, weather and
time. The nature and extent of such variations may not become evident until during or after
construction. Terracon should be retained as the Geotechnical Engineer, where noted in the final
report, to provide observation and testing services during pertinent construction phases. If
variations appear, we can provide further evaluation and supplemental recommendations. If
variations are noted in the absence of our observation and testing services on-site, we should be
immediately notified so that we can provide evaluation and supplemental recommendations.
Our scope of services does not include either specifically or by implication any environmental or
biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of
pollutants, hazardous materials or conditions. If the owner is concerned about the potential for
such contamination or pollution, other studies should be undertaken.
Our services and any correspondence or collaboration through this system are intended for the
sole benefit and exclusive use of our client for specific application to the project discussed and
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Responsive ■Resourceful ■Reliable 24
are accomplished in accordance with generally accepted geotechnical engineering practices with
no third party beneficiaries intended. Any third party access to services or correspondence is
solely for information purposes to support the services provided by Terracon to our client. Reliance
upon the services and any work product is limited to our client and is not intended for third parties.
Any use or reliance of the provided information by third parties is done solely at their own risk. No
warranties, either express or implied, are intended or made.
Site characteristics as provided are for design purposes and not to estimate excavation cost. Any
use of our report in that regard is done at the sole risk of the excavating cost estimator as there
may be variations on the site that are not apparent in the data that could significantly impact
excavation cost. Any parties charged with estimating excavation costs should seek their own site
characterization for specific purposes to obtain the specific level of detail necessary for costing.
Site safety, and cost estimating including, excavation support, and dewatering
requirements/design are the responsibility of others. If changes in the nature, design, or location
of the project are planned, our conclusions and recommendations shall not be considered valid
unless we review the changes and either verify or modify our conclusions in writing.
ATTACH MENTS
ATTACHMENTS
EXPLORATION AND TESTING PROCEDURES
SITE LOCATION AND EXPLORATION PLANS
EXPLORATION RESULTS
SUPPORTING INFORMATION
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Responsive ■Resourceful ■Reliable
EXPLORATION AND TESTING PROCEDURES
Field Exploration
Number of Borings Boring Depth (feet)Location
1 20 As close as practical to the
kitchen addition footprint
2 13 to 20 Within or as close as practical to
the rectory building footprint
Boring Layout and Elevations: The borings were located in the field by pacing or by
measurements with a mechanical surveying wheel using property boundaries and/or existing site
features as a reference. Right angles for locating the borings were estimated. Approximate ground
surface elevations at the boring locations for this exploration were obtained by interpolation from
contours indicated on the plan provided or by measurements with an engineer's level and rod
from a temporary bench mark (TBM) shown on the Exploration Plan. The latitude and longitude
coordinates of the boring locations were obtained by using a recreational-grade GPS device. The
accuracy of these coordinates is typically about +/- 10 to 15 feet. The accuracy of boring locations
and elevations should only be assumed to the level implied by the methods used.
Subsurface Exploration Procedures: Borings were advanced with a CME-45 truck-mounted
drilling rig, utilizing 4-inch diameter solid stem auger. Test boring TB-1 (drilled in the area of the
rectory building) encountered practical auger refusal on very hard bedrock at a depth of about 13
feet below ground surface. A geotechnical engineer recorded lithologic logs of each boring during
the drilling operations. At selected intervals, samples of the subsurface materials were taken by
means of driving a 2.5-inch O.D. modified California barrel sampler. Bulk samples (auger cuttings)
were also obtained from the test borings. Penetration resistance measurements were obtained
by driving the California barrel into the subsurface materials with a 140-pound hammer falling 30
inches. The penetration resistance value, when properly interpreted, is a useful index in
estimating the consistency, relative density, or hardness of the materials encountered.
Groundwater levels were recorded in each boring while drilling and shortly after (15 minutes to 3
hours) completion of drilling. Due to safety considerations, the borings were backfilled prior to
leaving the site; therefore, subsequent groundwater measurements were not obtained. Some
settlement of the backfill may occur over time and should be repaired as soon as possible.
A CME automatic hammer was used to advance the California barrel sampler in the borings
performed on this site. A greater efficiency is typically achieved with the automatic hammer
compared to the conventional safety hammer operated with a cathead and rope. Published
correlations between penetration values and soil properties are based on the lower efficiency
cathead and rope method. This higher efficiency affects the penetration resistance blow count
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Responsive ■Resourceful ■Reliable
value by increasing the penetration per hammer blow over what would be obtained using the
cathead and rope method. The effect of the automatic hammer’s efficiency has been considered
in the interpretation and analysis of the subsurface information for this report.
The penetration test provides a reasonable indication of the in-place density of sandy type
materials, but only provides an indication of the relative stiffness of cohesive materials since the
blow count in these soils may be affected by the soil’s moisture content. In addition, considerable
care should be exercised in interpreting the penetration values in gravelly soils, particularly where
the size of the gravel particle exceeds the inside diameter of the sampler.
Laboratory Testing
Samples retrieved during the field exploration were returned to the laboratory for observation by
the project geotechnical engineer and were visually classified in general accordance with the
Unified Soil Classification System described in the Supporting Information section of this report.
Samples of bedrock were classified in accordance with the general notes for Rock Classification.
After sample review by the project engineer, an applicable laboratory testing program was
formulated to determine engineering properties of the subsurface materials. Following completion
of the laboratory testing, the field and visual descriptions were confirmed or modified as
necessary, and Logs of Borings were prepared. These logs are presented in the Exploration
Results section of this report.
Selected samples were tested for the following physical and/or engineering properties:
■Moisture Content
■Dry Unit Weight
■Swell-Consolidation Potential
■Percent Fines/Grain Size
■Atterberg Limits
■Water Soluble Sulfate Content
Laboratory test results are indicated on the boring logs and are presented in depth in the
Exploration Results section. The test results are used for the geotechnical engineering analyses
and the development of foundation, on-grade slab and earthwork recommendations. Laboratory
tests are performed in general accordance with applicable local standards or other accepted
standards. Procedural standards noted in this report are for reference to methodology in general.
In some cases, variations to methods are applied as a result of local practice or professional
judgment.
Descriptive classifications of the soils indicated on the boring logs are in accordance with the
enclosed General Notes and the Unified Soil Classification System. Also shown are estimated
Geotechnical Engineering Report
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Responsive ■Resourceful ■Reliable
Unified Soil Classification Symbols. A brief description of this classification system as well as the
General Notes can be found in the Supporting Information section. Classification was by visual-
manual procedures. Selected samples were further classified using the results of Atterberg limit
and percent fines/grain size distribution testing. The Atterberg limit test results are also provided
in the Exploration Results section.
SITE LOCA TION AND EXPLORATI ON PLANS
SITE LOCATION AND EXPLORATION PLANS
SITE LOCATION
OLM New Rectory Building and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT
INTENDED FOR CONSTRUCTION PURPOSES AERIAL PHOTOGRAPHY PROVIDED BY
MICROSOFT BING MAPS
SITE
LEGEND:0’50’100’
APPROX. GRAPHIC SCALEAPPROXIMATE LOCATION OF
TEST BORING DRILLED ON
JANUARY 22, 2020
S.
T
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Scale:
1831 Lefthand Circle Longmont, Colorado 80501
PH. (303) 776-3921 FAX. (303) 776-4041
ESW
ESW
EDB
ESW
Project Manager:
Drawn by:
Checked by:
Approved by:
EXPLORATION PLAN
1/22/2020
1” = 100’ +/-
Project No.
File Name:
Date:DIAGRAM IS FOR GENERAL LOCATION ONLY, AND
IS NOT INTENDED FOR CONSTRUCTION PURPOSES
OUR LADY OF THE MOUNTAINS CATHOLIC CHURCH
OLM NEW RECTORY BUILDING & KITCHEN ADDITION
920 BIG THOMPSON AVE./HWY 34
ESTES PARK, COLORADO
22195040
22195040 EP
VICINITY MAP
N.T.S.
TEMPORARY BENCH MARK (TBM)
MIDDLE OF CONCRETE WALK
APPROXIMATE ELEV. = 7530 FEET +/-
TB-2
TB-3
TB-1
PROJECT
SITE
EXPLORATION RESULTS
EXPLORATION RESULTS
50/7"
50/1"
50/4"
50/1"
22
3
3
119
NP
VEGETATIVE SOIL LAYER, Sandy soil with vegetation
and root penetration
SILTY SAND (SM), light brown, olive brown, fine to coarse
grained, trace fine GRAVEL
BIOTITE SCHIST, (Metamorphic Bedrock), pink,
tan/beige, orange to olive, grey, weathered to very hard, with
mica
Very hard drilling below about 6 to 7 feet
PRACTICAL AUGER REFUSAL at 13.5 Feet
0.3
2.0
13.5
7538.5+/-
7537+/-
7525.5+/-
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.
TH
I
S
B
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L
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4
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5
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,
(
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PE
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(
%
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(
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)
ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 40.3814° Longitude: -105.5093°
GR
A
P
H
I
C
L
O
G
DEPTH ELEVATION (Ft.)
Approximate Surface Elev.: 7539 (Ft.) +/-
Page 1 of 1
Advancement Method:
4-inch diameter solid stem auger
Abandonment Method:
Boring backfilled with auger cuttings after delayed water
level was measured.
Notes:
Project No.: 22195040
Drill Rig: CME-45
BORING LOG NO. TB-1
Our Lady of the Mountains Catholic ChurchCLIENT:
Estes Park, CO
Driller: ODELL
Boring Completed: 01-22-2020
PROJECT: Our Lady of the Mtns. Catholic Church -
Rectory & Kitchen Addn.
Elevation was measured in the field using an
engineer's level and rod.
See Exploration and Testing Procedures for a
description of field and laboratory procedures
used and additional data (If any).
See Supporting Information for explanation of
symbols and abbreviations.
920 Big Thompson Avenue
Estes Park, Colorado
SITE:
Boring Started: 01-22-2020
1831 Lefthand Cir Ste C
Longmont, CO
None encountered after completion of drilling
DCI at 12 feet when checked 1.5 hrs. after drilling
WATER LEVEL OBSERVATIONS
SA
M
P
L
E
T
Y
P
E
50/8"
50/6"
50/2"
50/2"
50/3"
50/2"
3
2
1
2
2
3
119
121
VEGETATIVE SOIL LAYER, Sandy soil with vegetation
and root penetration
SILTY SAND (SM), light brown, brown, fine to medium
grained
BIOTITE SCHIST, (Metamorphic Bedrock), light grey, rust,
tan to pink, tan/white, orange, olive, weathered to very hard,
with mica
Very hard lenses below about 6 feet
Boring Terminated at 19.5 Feet
0.3
1.5
19.5
7526.5+/-
7525.5+/-
7507.5+/-
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.
TH
I
S
B
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I
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G
L
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I
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10
15
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(
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(
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(
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)
ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 40.3813° Longitude: -105.5092°
GR
A
P
H
I
C
L
O
G
DEPTH ELEVATION (Ft.)
Approximate Surface Elev.: 7527 (Ft.) +/-
Page 1 of 1
Advancement Method:
4-inch diameter solid stem auger
Abandonment Method:
Boring backfilled with auger cuttings after delayed water
level was measured.
Notes:
Project No.: 22195040
Drill Rig: CME-45
BORING LOG NO. TB-2
Our Lady of the Mountains Catholic ChurchCLIENT:
Estes Park, CO
Driller: ODELL
Boring Completed: 01-22-2020
PROJECT: Our Lady of the Mtns. Catholic Church -
Rectory & Kitchen Addn.
Elevation was measured in the field using an
engineer's level and rod.
See Exploration and Testing Procedures for a
description of field and laboratory procedures
used and additional data (If any).
See Supporting Information for explanation of
symbols and abbreviations.
920 Big Thompson Avenue
Estes Park, Colorado
SITE:
Boring Started: 01-22-2020
1831 Lefthand Cir Ste C
Longmont, CO
None encountered after completion of drilling
DCI at 18.5 feet when checked 3 hrs. after drilling
WATER LEVEL OBSERVATIONS
SA
M
P
L
E
T
Y
P
E
13/12"
10/12"
50/12"
50/6"
50/4"
50/7"
-0.5/500
-0.3/1000 14
7
8
5
2
2
4
119
115
133
25-21-4
FILL; SILTY, CLAYEY SAND (SC-SM), with GRAVEL,
mottled dark brown, orange brown, rust, loose, fine to coarse
grained
BIOTITE SCHIST, (Metamorphic Bedrock), orange brown,
grey, rust to to pink, tan/white, orange, grey, weathered to
very hard, with mica
Intermittent very hard lenses below about 10 feet
Boring Terminated at 19.5 Feet
6.5
19.5
7543.5+/-
7530.5+/-
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.
TH
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B
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5
10
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LO
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(
%
/
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)
PE
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WA
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(
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I
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WE
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(
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f
)
ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 40.3816° Longitude: -105.5079°
GR
A
P
H
I
C
L
O
G
DEPTH ELEVATION (Ft.)
Approximate Surface Elev.: 7550 (Ft.) +/-
Page 1 of 1
Advancement Method:
4-inch diameter solid stem auger
Abandonment Method:
Boring backfilled with auger cuttings after completion of
drilling.
Notes:
Project No.: 22195040
Drill Rig: CME-45
BORING LOG NO. TB-3
Our Lady of the Mountains Catholic ChurchCLIENT:
Estes Park, CO
Driller: ODELL
Boring Completed: 01-22-2020
PROJECT: Our Lady of the Mtns. Catholic Church -
Rectory & Kitchen Addn.
Elevation was interpolated from a topographic
site plan.
See Exploration and Testing Procedures for a
description of field and laboratory procedures
used and additional data (If any).
See Supporting Information for explanation of
symbols and abbreviations.
920 Big Thompson Avenue
Estes Park, Colorado
SITE:
Boring Started: 01-22-2020
1831 Lefthand Cir Ste C
Longmont, CO
None encountered after completion of drilling
Backfilled after completion of drilling
WATER LEVEL OBSERVATIONS
SA
M
P
L
E
T
Y
P
E
-10
-8
-6
-4
-2
0
2
4
6
8
10
100 1,000 10,000 105
AX
I
A
L
S
T
R
A
I
N
,
%
PRESSURE, psf
NOTES: Sample exhibited 0.5 percent compression upon wetting under an applied pressure of 500 psf.
SWELL CONSOLIDATION TEST
PROJECT NUMBER: 22195040
SITE: 920 Big Thompson Avenue
Estes Park, Colorado
PROJECT: Our Lady of the Mtns. Catholic
Church - Rectory & Kitchen Addn.
CLIENT: Our Lady of the Mountains Catholic
Church
Estes Park, CO
1831 Lefthand Cir Ste C
Longmont, CO
LA
B
O
R
A
T
O
R
Y
T
E
S
T
S
A
R
E
N
O
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V
A
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I
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A
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P
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.
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_
C
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S
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_
S
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A
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N
-
U
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C
S
-
N
O
A
S
T
M
2
2
1
9
5
0
4
0
O
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A
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Y
O
F
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M
.
G
P
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R
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A
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N
_
D
A
T
A
T
E
M
P
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A
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E
.
G
D
T
1
/
2
7
/
2
0
119 7TB-3 FILL; SILTY, CLAYEY SAND (SC-SM)2 - 3 ft
Specimen Identification Classification , pcf WC, %
-10
-8
-6
-4
-2
0
2
4
6
8
10
100 1,000 10,000 105
AX
I
A
L
S
T
R
A
I
N
,
%
PRESSURE, psf
NOTES: Sample exhibited 0.3 percent compression upon wetting under an applied pressure of 1,000 psf.
SWELL CONSOLIDATION TEST
PROJECT NUMBER: 22195040
SITE: 920 Big Thompson Avenue
Estes Park, Colorado
PROJECT: Our Lady of the Mtns. Catholic
Church - Rectory & Kitchen Addn.
CLIENT: Our Lady of the Mountains Catholic
Church
Estes Park, CO
1831 Lefthand Cir Ste C
Longmont, CO
LA
B
O
R
A
T
O
R
Y
T
E
S
T
S
A
R
E
N
O
T
V
A
L
I
D
I
F
S
E
P
A
R
A
T
E
D
F
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O
M
O
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I
G
I
N
A
L
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E
P
O
R
T
.
T
C
_
C
O
N
S
O
L
_
S
T
R
A
I
N
-
U
S
C
S
-
N
O
A
S
T
M
2
2
1
9
5
0
4
0
O
U
R
L
A
D
Y
O
F
T
H
E
M
.
G
P
J
T
E
R
R
A
C
O
N
_
D
A
T
A
T
E
M
P
L
A
T
E
.
G
D
T
1
/
2
7
/
2
0
115 8TB-3 FILL; SILTY, CLAYEY SAND (SC-SM)4 - 5 ft
Specimen Identification Classification , pcf WC, %
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
30 40 501.5 200681014413/4 1/2 60
GRAIN SIZE IN MILLIMETERS
PE
R
C
E
N
T
F
I
N
E
R
B
Y
W
E
I
G
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T
HYDROMETERU.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
4 3/8 3 100 14032
GRAIN SIZE DISTRIBUTION
ASTM D422 / ASTM C136
6 16 20
PROJECT NUMBER: 22195040
SITE: 920 Big Thompson Avenue
Estes Park, Colorado
PROJECT: Our Lady of the Mtns. Catholic
Church - Rectory & Kitchen Addn.
CLIENT: Our Lady of the Mountains Catholic
Church
Estes Park, CO
1831 Lefthand Cir Ste C
Longmont, CO
LA
B
O
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A
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O
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Y
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S
T
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A
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N
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F
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9
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4
0
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1
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medium
TB-1
TB-3
coarse coarsefine fineCOBBLESGRAVELSAND SILT OR CLAY
SILTY SAND (SM)
SILTY, CLAYEY SAND with GRAVEL (SC-SM)
NP
25
21.5
13.7
TB-1
TB-3
NP
4
NP
21
0.5 - 2
4 - 5
0.5 - 2
4 - 5
2.3
22.9
76.2
63.4
9.5
25
0.337
1.908
0.115
0.338
Boring ID Depth WC (%)LL PL PI Cc Cu
%Clay%Fines%Silt%Sand%Gravel Boring ID Depth D100 D60 D30 D10
USCS Classification
%Cobbles
0.0
0.0
SUPPORTING INFORMA TION
SUPPORTING INFORMATION
GENERAL NOTES
OLM New Rectory and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
UNIFIED SOIL CLASSIFICATION SYSTEM
OLM New Rectory and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests A
Soil Classification
Group
Symbol Group Name B
Coarse-Grained Soils:
More than 50% retained
on No. 200 sieve
Gravels:
More than 50% of
coarse fraction
retained on No. 4
sieve
Clean Gravels:
Less than 5% fines C
Cu 4 and 1 Cc 3 E GW Well-graded gravel F
Cu 4 and/or 1 Cc 3 E GP Poorly graded gravel F
Gravels with Fines:
More than 12% fines C
Fines classify as ML or MH GM Silty gravel F,G,H
Fines classify as CL or CH GC Clayey gravel F,G,H
Sands:
50% or more of coarse
fraction passes No. 4
sieve
Clean Sands:
Less than 5% fines D
Cu 6 and 1 Cc 3 E SW Well-graded sand I
Cu 6 and/or 1 Cc 3 E SP Poorly graded sand I
Sands with Fines:
More than 12% fines D
Fines classify as ML or MH SM Silty sand G,H,I
Fines classify as CL or CH SC Clayey sand G,H,I
Fine-Grained Soils:
50% or more passes
the No. 200 sieve
Silts and Clays:
Liquid limit less than
50
Inorganic: PI 7 and plots on or above “A”
line J
CL Lean clay K,L,M
PI 4 or plots below “A” line J ML Silt K,L,M
Organic: Liquid limit - oven dried 0.75 OL Organic clay K,L,M,N
Liquid limit - not dried Organic silt K,L,M,O
Silts and Clays:
Liquid limit 50 or more
Inorganic: PI plots on or above “A” line CH Fat clay K,L,M
PI plots below “A” line MH Elastic Silt K,L,M
Organic: Liquid limit - oven dried 0.75 OH Organic clay K,L,M,P
Liquid limit - not dried Organic silt K,L,M,Q
Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat
A Based on the material passing the 3-inch (75-mm) sieve
B If field sample contained cobbles or boulders, or both, add “with cobbles
or boulders, or both” to group name.
C Gravels with 5 to 12% fines require dual symbols: GW -GM well-graded
gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly
graded gravel with silt, GP-GC poorly graded gravel with clay.
D Sands with 5 to 12% fines require dual symbols: SW -SM well-graded
sand with silt, SW -SC well-graded sand with clay, SP-SM poorly graded
sand with silt, SP-SC poorly graded sand with clay
E Cu = D60/D10 Cc =
6010
2
30
DxD
)(D
F If soil contains 15% sand, add “with sand” to group name.
G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.
H If fines are organic, add “with organic fines” to group name.
I If soil contains 15% gravel, add “with gravel” to group name.
J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.
K If soil contains 15 to 29% plus No. 200, add “with sand” or “with
gravel,” whichever is predominant.
L If soil contains 30% plus No. 200 predominantly sand, add
“sandy” to group name.
M If soil contains 30% plus No. 200, predominantly gravel, add
“gravelly” to group name.
N PI 4 and plots on or above “A” line.
O PI 4 or plots below “A” line.
P PI plots on or above “A” line.
Q PI plots below “A” line.
DESCRIPTION OF ROCK PROPERTIES
OLM New Rectory and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
DESCRIPTION OF ROCK PROPERTIES
(Based on ASTM C-294)
Metamorphic Rocks
Metamorphic rocks form from igneous, sedimentary, or pre-existing metamorphic rocks in response to changes
in chemical and physical conditions occurring within the earth’s crust after formation of the original rock. The
changes may be textural, structural, or mineralogic and may be accompanied by changes in chemical
composition. The rocks are dense and may be massive but are more frequently foliated (laminated or layered)
and tend to break into platy particles. The mineral composition is very variable depending in part on the degree
of metamorphism and in part on the composition of the original rock.
Marble A recrystallized medium- to coarse-grained carbonate rock composed of calcite or
dolomite, or calcite and dolomite. The original impurities are present in the form of new
minerals, such as micas, amphiboles, pyroxenes, and graphite.
Metaquartzite A granular rock consisting essentially of recrystallized quartz. Its strength and
resistance to weathering derive from the interlocking of the quartz grains.
Slate A fine-grained metamorphic rock that is distinctly laminated and tends to split into thin
parallel layers. The mineral composition usually cannot be determined with the unaided
eye.
Schist A highly layered rock tending to split into nearly parallel planes (schistose) in which the
grain is coarse enough to permit identification of the principal minerals. Schists are
subdivided into varieties on the basis of the most prominent mineral present in addition
to quartz or to quartz and feldspars; for instance, mica schist. Greenschist is a green
schistose rock whose color is due to abundance of one or more of the green minerals,
chlorite or amphibole, and is commonly derived from altered volcanic rock.
Gneiss One of the most common metamorphic rocks, usually formed from igneous or
sedimentary rocks by a higher degree of metamorphism than the schists. It is
characterized by a layered or foliated structure resulting from approximately parallel
lenses and bands of platy minerals, usually micas or prisms, usually amphiboles, and of
granular minerals, usually quartz and feldspars. All intermediate varieties between
gneiss and schist and between gneiss and granite are often found in the same areas in
which well-defined gneisses occur.
UNIFIED SOIL CLASSIFICATION SYSTEM
OLM New Rectory and Kitchen Addition ■ Estes Park, Colorado
February 14, 2020 ■ Terracon Project No. 22195040
DESCRIPTION OF ROCK PROPERTIES
(Based on ASTM C-294)
Igneous Rocks
Igneous rocks are formed by cooling from a molten rock mass (magma). Igneous rocks are divided into two
classes (1) plutonic, or intrusive, that have cooled slowly within the earth; and (2) volcanic, or extrusive, that
formed from quickly cooled lavas. Plutonic rocks have grain sizes greater than approximately 1 mm, and are
classified as coarse- or medium-grained. Volcanic rocks have grain sizes less than approximately 1 mm, and
are classified as fine-grained. Volcanic rocks frequently contain glass. Both plutonic and volcanic rocks may
consist of porphyries that are characterized by the presence of large mineral grains in a fine -grained or glassy
groundmass. This is the result of sharp changes in rate of cooling or other physico-chemical conditions during
solidification of the melt.
Granite Granite is a medium- to coarse-grained light-colored rock characterized by the
presence of potassium feldspar with lesser amounts of plagioclase feldspars and
quartz. The characteristic potassium feldspars are othoclase or microcline, or both;
the common plagioclase feldspars are albite and oligoclase. Feldspars are more
abundant than quartz. Dark-colored mica (biotite) is usually present, and light-
colored mica (muscovite) is frequently present. Other dark-colored ferromagnesian
minerals, especially honblende, may be present in amounts less than those of the
light-colored constituents.
Quartz-Monzonite Rocks similar to granite but contain more plagioclase feldspar than potassium
and Grano-Diorite feldspar.
Basalt Fine-grained extrusive equivalent of gabbro and diabase. When basalt contains
natural glass, the glass is generally lower in silica content than that of the lighter -
colored extrusive rocks.