HomeMy WebLinkAboutKECHTER TOWNHOMES - FDP210002 - - GEOTECHNICAL (SOILS) REPORT400 North Link Lane | Fort Collins, Colorado 80524
Telephone: 970-206-9455 Fax: 970-206-9441
SOIL AND FOUNDATION INVESTIGATION
MULTI-FAMILY RESIDENCES
54 LOTS (11 BUILDINGS) 3620 E KECHTER ROAD
FORT COLLINS, COLORADO
Prepared For:
TWG DEVELOPMENT, LLC
333 North Pennsylvania Street, Suite 100
Indianapolis, Indiana 46204
Attention: Ryan Kelly
Project No. FC08892.001-120
March 1, 2021
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120
TABLE OF CONTENTS
SCOPE 1
SUMMARY OF CONCLUSIONS 1
SITE CONDITIONS 3
PROPOSED CONSTRUCTION 3
INVESTIGATION 3
SUBSURFACE CONDITIONS 4
GEOLOGIC HAZARDS 5
FOUNDATIONS 6
Footings with Minimum Dead Load 6
FLOOR SYSTEMS AND SLAB-ON-GRADE FLOORS 8
Slab Performance Risk 8
Structurally Supported Floors 8
Porches, Decks and Patios 10
Garage Slabs and Exterior Flatwork 11
OVER-EXCAVATION 11
BELOW-GRADE WALLS 12
BACKFILL COMPACTION 12
SUBSURFACE DRAINS AND SURFACE DRAINAGE 14
CONCRETE 15
EXCAVATIONS 15
CONSTRUCTION OBSERVATIONS 16
GEOTECHNICAL RISK 16
LIMITATIONS 16
FIGURE 1 – DEVELOPMENT PLAN
FIGURE 2 – OVER-EXCAVATION DEPTHS
APPENDIX A – SUMMARY LOGS OF EXPLORATORY BORINGS
APPENDIX B – RESULTS OF LABORATORY TESTS
Table B-1 – Summary of Laboratory Testing
Table B-2 – Summary of Ground Heave Estimates
EXHIBIT A – SLAB PERFORMANCE RISK EVALUATION, INSTALLATION AND
MAINTENANCE
EXHIBIT B – SURFACE DRAINAGE, IRRIGATION AND MAINTENANCE
EXHIBIT C – EXAMPLE BACKFILL COMPACTION ALTERNATIVES
TWG DEVELOPMENT, LLC
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SCOPE
This report presents the results of our Soils and Foundation Investigation
for 54 proposed multi-family residences located at the subject address in Fort
Collins, Colorado (Figure 1). The purpose of our investigation was to evaluate the
subsurface conditions in order to provide geotechnical design and construction
recommendations for the proposed residences. The scope was described in our
Service Agreement (Proposal No. FC-21-0027) dated January 18, 2021).
This report was prepared from data developed during field exploration,
laboratory testing, engineering analysis, and experience with similar conditions. It
includes our opinions and recommendations for design criteria and construction
details for foundations and floor systems, slabs-on-grade, lateral earth loads, and
drainage precautions. The report was prepared for the exclusive use of TWG
Development, LLC in design and construction of single-family residences in the
referenced subdivision. Other types of construction may require revision of this
report and the recommended design criteria. A brief summary of our conclusions
and recommendations follows. Detailed design criteria are presented within the
report.
SUMMARY OF CONCLUSIONS
1. Near-surface soils encountered in our borings consisted primarily of
sandy, silty clay. Sand-dominate and silt-dominate strata were
occasionally encountered in our borings. Clean to clayey sand and
gravel were encountered underlying the sandy clay in twelve of the
borings from 11 to 19 feet to the depths explored. Weathered
claystone bedrock was encountered in one boring at a depth of 23
feet to the depths explored.
2. Groundwater was measured at depths ranging from 14 to 21 feet in
fifteen borings during drilling. When measured several days later,
groundwater was encountered at depths of 12 ½ to 18 ½ feet across
all borings. Existing groundwater levels are not expected to
significantly affect site development. We recommend a minimum 3-
foot separation between foundation elements and groundwater.
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3. The presence of expansive soils and bedrock, and possibly
collapsing soils, constitutes a geologic hazard. There is risk that
slabs-on-grade and foundations will heave or settle and be
damaged. We judge the risk is moderate to high. We believe the
recommendations presented in this report will help to control risk of
damage; they will not eliminate that risk. Slabs-on-grade and, in
some instances, foundations may be damaged.
4. Footing foundations designed to maintain a minimum dead load
placed on properly over-excavated, moisture conditioned and
recompacted fill are considered appropriate for the lots included.
The recommended over-excavation depth for each building is shown
on Figure 2. Design and construction criteria for foundations are
presented in the report.
5. Soft soils were encountered in our borings. If soft soils are
encountered at the bottom of the foundation excavation, stabilization
can likely be achieved by crowding 1½ to 3-inch nominal size
crushed rock into the subsoils until the base of the excavation does
not deform by more than about ½-inch when compactive effort is
applied.
6. The risk of poor slab performance is rated moderate to high for the
lots included. Driveways and other exterior flatwork will be slabs-on-
grade and may heave or settle and crack.
7. Surface drainage should be designed, constructed and maintained
to provide rapid removal of surface runoff away from the proposed
residences. Conservative irrigation practices should be followed to
avoid excessive wetting.
8. The design and construction criteria for foundations and floor system
alternatives in this report were compiled with the expectation that all
other recommendations presented related to surface and subsurface
drainage, landscaping irrigation, backfill compaction, etc. will be
incorporated into the project and that homeowners will maintain the
structures, use prudent irrigation practices and maintain surface
drainage. It is critical that all recommendations in this report are
followed.
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SITE CONDITIONS
The site is located in southeast Fort Collins, Colorado (Figure 1). During
the time of our investigation, the site was occupied by an existing residence.
Several outbuildings and livestock pens were observed at the site. Ground cover
consisted of natural grasses and weeds. The site is relatively flat, sloping down
gradually toward the southwest corner of the site. A stormwater pond was
observed west of the site.
PROPOSED CONSTRUCTION
The proposed residences are anticipated to be wood-framed, one or two-
story structures with attached garages. The residences may have partial brick or
stone veneer on the exterior. Foundation loads are expected to vary between
1,000 and 3,000 pounds per lineal foot of foundation wall, with individual column
loads of 25 kips or less.
INVESTIGATION
The field investigation included drilling sixteen exploratory borings across
the proposed lots. The borings were drilled to depths of approximately 20 feet and
25 feet using 4-inch diameter, continuous-flight augers and a truck-mounted drill.
Drilling was observed by our field representative who logged the soils and bedrock.
Summary logs of the borings, including results of field penetration resistance tests,
are presented in Appendix A.
Soil and bedrock samples obtained during drilling were returned to our
laboratory and visually examined by our geotechnical engineer. Laboratory testing
was assigned and included moisture content, dry density, swell-consolidation,
particle-size analysis, Atterberg limits, and water-soluble sulfate tests. Swell-
consolidation test samples were wetted at a confining pressure which
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approximated the weight of overlying soils (overburden pressures). Results of the
laboratory tests are presented in Appendix B.
SUBSURFACE CONDITIONS
Near-surface soils encountered in our borings consisted primarily of sandy,
silty clay. Sand-dominate and silt-dominate strata were occasionally encountered
in our borings. Clean to clayey sand and gravel were encountered underlying the
sandy clay in twelve of the borings from 11 to 19 feet to the depths explored.
Weathered claystone bedrock was encountered in one boring at a depth of 23 feet
to the depths explored. Groundwater was measured at depths ranging from 14 to
21 feet in fifteen borings during drilling. When measured several days later,
groundwater was encountered at depths of 12½ to 18½ feet across all borings.
Table A provides a summary of the swell test results. Further descriptions of the
subsurface conditions are presented on our boring logs and in our laboratory test
results.
TABLE A
SUMMARY OF SWELL TEST RESULTS
Soil Type
Compression
Range of Measured Swell (%)*
0 to <2 2 to <4 4 to
<6 6
Number of Samples and Percent
Sandy, Silty Clay 1 6 6 6 2
5% 29% 29% 29% 10%
Clayey, Silty Sand 1 0 1 0 0
50% 0% 50% 0% 0%
Clayey, Sandy Silt 0 1 1 0 0
0% 50% 50% 0% 0%
Overall Sample Number 2 7 8 6 2
Overall Percent 8% 28% 32% 24% 8%
* Swell measured after wetting under the approximate weight of the overlying soils (overburden pressures).
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GEOLOGIC HAZARDS
Colorado is a challenging location to practice geotechnical engineering. The
climate is relatively dry and the near-surface soils are typically dry and relatively
stiff. These soils and related sedimentary bedrock formations tend to react to
changes in moisture conditions. Some of the soils and bedrock swell as they
increase in moisture and are called expansive soils. Other soils can settle
significantly upon wetting and are referred to as collapsing soils. Most of the land
available for development east of the Front Range is underlain by expansive clay
or claystone bedrock near the surface. The soils that exhibit collapse are more
likely west of the continental divide; however, both types of soils occur all over the
state.
Covering the ground with houses, streets, driveways, patios, etc., coupled
with lawn irrigation and changing drainage patterns, leads to an increase in
subsurface moisture conditions. As a result, some soil movement is inevitable. It
is critical that all recommendations in this report are followed to increase the
chances that the foundations and slabs-on-grade will perform satisfactorily. After
construction, homeowners must assume responsibility for maintaining the
structure and use appropriate practices regarding drainage and landscaping.
Expansive soils and bedrock are present at this site. The presence of
expansive soils and bedrock, collectively referred to as expansive or swelling soils,
constitutes a geologic hazard. Some near-surface soils may also compress, or
collapse, when wetted. There is risk that ground heave or settlement will damage
slabs-on-grade and foundations. The risks associated with swelling and
compressible soils can be mitigated, but not eliminated by careful design,
construction and maintenance procedures.
We believe the recommendations in this report will help control risk of
foundation and/or slab damage; they will not eliminate that risk. The builder and
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homebuyers should understand that slabs-on-grade and, in some instances,
foundations may be affected. Homeowner maintenance will be required to control
risk. We recommend the builder provide a booklet to the homebuyers that
describes swelling soils and includes recommendations for care and maintenance
of homes constructed on expansive soils. Colorado Geological Survey Special
Publication 431 was designed to provide this information.
FOUNDATIONS
Our investigation indicates swelling and potentially collapsible soils were
encountered at depths where they are likely to affect foundation performance.
Footing foundations designed to maintain minimum deadload are considered
appropriate for the proposed construction if placed on over-excavated materials.
The recommended over-excavation depth for each building is shown on Figure 2.
Design criteria for footing foundations developed from analysis of field and
laboratory data and our experience are presented below. The builder and structural
engineer should also consider design and construction details established by the
structural warrantor (if any) that may impose additional design and installation
requirements.
Footings with Minimum Dead Load
1. The footing foundation should bear on a minimum depth of properly
over-excavated fill per Figure 2. Where soils are loosened during
excavation or in the footing forming process the soils should be
removed or compacted to at least 95 percent of standard Proctor
maximum dry density (ASTM D 698, AASHTO T 99) between
optimum and 3 percent above optimum moisture content, prior to
placing concrete. Excavation backfill placed below foundations
should be compacted using the same specifications.
1“A Guide to Swelling Soils for Colorado Homebuyers and Homeowners,” Second Edition Revised and Updated
by David C. Noe, Colorado Geological Survey, Department of Natural Resources, Denver, Colorado, 2007.
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2. Soft soils were encountered in our borings. If soft soils are
encountered, stabilization can likely be achieved by crowding 1½ to
3-inch nominal size crushed rock into the subsoils until the base of
the excavation does not deform by more than about ½-inch when
compactive effort is applied.
3. Footings should be designed for a net allowable soil pressure of
3,000 pounds per square foot (psf) and a minimum dead load
pressure of 1,000 psf. The soil pressure can be increased 33 percent
for transient loads such as wind or seismic loads. We recommend a
minimum 3-foot separation between foundation elements and
groundwater.
4. We anticipate footings designed using the soil pressure
recommended above could experience 1-inch of movement.
Differential movement of ½-inch should be considered in the design.
5. If interrupted footings are necessary to maintain the specified dead
load, a 4-inch void should be provided below grade beams or
foundation walls, between the pads.
6. Footings should have a minimum width of 16 inches. Foundations
for isolated columns should have minimum dimensions of 20 inches
by 20 inches. Larger sizes may be required depending upon the
loads and structural system used.
7. Foundation walls should be well-reinforced, top and bottom. We
recommend reinforcement sufficient to span an unsupported
distance of at least 10 feet or the distance between pads whichever
is greater. Reinforcement should be designed by the structural
engineer considering the effects of large openings and lateral loads
on wall performance.
8. Exterior footings must be protected from frost action per local
building codes. Normally, 30 inches of cover over footings is
assumed in the area for frost protection.
9. The completed foundation excavations should be observed by a
representative of our firm prior to placing the forms to verify
subsurface conditions are as anticipated from our borings. Our
representative should also observe the placement and test
compaction of new fill placed for foundation subgrade (if merited).
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FLOOR SYSTEMS AND SLAB-ON-GRADE FLOORS
Slab Performance Risk
We conducted swell-consolidation testing to provide a basis for calculating
potential soil heave at this site. We estimate potential heave of 5 ½ inches or less
for the lots included if no swell mitigation measures are performed. Table B-2 in
Appendix B summarizes the heave estimates along with the estimated remaining
heave following the swell mitigation. A depth of wetting of 24 feet was considered
for our heave evaluation. Recent research (Walsh, Colby, Houston and Houston,
ASCE, 2009) indicates there is a 90 percent probability that the wetting depth will
not exceed 24 feet in this region, suggesting that the risk of ground heave
exceeding the estimated values is low.
Based on our heave calculations, the subsurface conditions found in our
borings, and our experience with residence construction and performance, we
judge that the risk of poor slab-on-grade performance at this site is moderate to
high. If floor movements cannot be tolerated, homebuyers should select a lot
where a structurally supported floor system is constructed or request that one be
installed. Slab heave of 3 to 5 inches is not uncommon in areas rated as high risk.
Slab subgrade should be over-excavated to match recommendations for the
buildings to reduce potential heave risk. A more detailed discussion of slab-on-
grade performance risk and construction recommendations is provided in Exhibit
A.
Structurally Supported Floors
Structural floors should be used in non-basement, finished living areas if
floor movement and cracking are unacceptable. A structural floor is supported by
the foundation system. There are design and construction issues associated with
structural floors that must be considered, such as ventilation and lateral loads.
Where structurally supported floors are installed, the required air space depends
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on the materials used to construct the floor and the expansion potential of the
underlying soils. Building codes require a clear space of 18 inches above exposed
earth if untreated wood floor components are used. Where other floor support
materials are used, a minimum clear space of 14 inches should be maintained.
This minimum clear space should be maintained between any point on the
underside of the floor system (including beams and floor drain traps) and the
surface of the exposed earth.
Where structurally supported floors are used, utility connections, including
water, gas, air duct and exhaust stack connections to floor supported appliances,
should be capable of absorbing some deflection of the floor. Plumbing that passes
through the floor should ideally be hung from the underside of the structural floor
and not lain on the bottom of the excavation. This configuration may not be
achievable for some parts of the installation. It is prudent to maintain the minimum
clear space below all plumbing lines. If trenching below the lines is necessary, we
recommend sloping these trenches so they discharge to the foundation drains.
Control of humidity in crawl spaces is important for indoor air quality and
performance of wood floor systems. We believe the best current practices to
control humidity involve the use of a vapor retarder (10-mil minimum), placed on
the exposed soils below accessible sub-floor areas. The vapor retarder should be
sealed at joints and attached to concrete foundation elements. If desired, we can
provide designs for ventilation systems that can be installed in association with a
vapor retarder, to improve control of humidity in crawl space areas. The Moisture
Management Task Force of Metro Denver2 has compiled additional discussion and
recommendations regarding best practices for the control of humidity in below-
grade, under-floor spaces.
2 “Guidelines for Design and Construction of New Homes with Below-Grade Under-Floor Spaces,” Moisture Management
Task Force, October 30, 2003.
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Porches, Decks and Patios
Porches or decks with overhanging roofs that are integral with the residence
such that excessive foundation movement cannot be tolerated, should be
constructed with the same foundation type as the house. Simple decks, that are
not integral with the residence and can tolerate foundation movement, can be
constructed with less substantial foundations. A short pier or footing bottomed at
least 3 feet below grade can be used if movement is acceptable. Use of 8-foot to
10-foot piers can reduce potential movement. Footings or short piers should not
be bottomed in wall backfill or undocumented fill due to risk of settlement. The
inner edge of the deck may be constructed on haunches or steel angles bolted to
the foundation walls and detailed such that movement of the deck foundation will
not cause distress to the residences. We suggest use of adjustable bracket-type
connections or other details between foundations and deck posts so the posts can
be trimmed or adjusted if movement occurs.
Porches, patio slabs and other exterior flatwork should be isolated from the
structures. Porch slabs can be constructed to reduce the likelihood that settlement
or heave will affect the slabs. One approach (for smaller porches located over
basement backfill zones) is to place loose backfill under a structurally supported
slab. This fill will more likely settle than swell, and can thus accommodate some
heave of the underlying soils. A lower risk approach is to construct the porch slab
over void-forming materials. Conditions should allow the void-forming materials to
soften quickly after construction to reduce the risk of transmitting ground heave to
the porch slab. Wax or plastic-coated void boxes should not be used unless
provisions are made to allow water to penetrate into the boxes.
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Garage Slabs and Exterior Flatwork
Garage floors, driveways and sidewalks are normally constructed as slabs-
on-grade. Performance of conventional slabs on expansive soils is erratic. Various
properties of the soils and environmental conditions influence magnitude of
movement and other performance. Increases in the moisture content in these soils
will cause heaving and may result in cracking of slabs-on-grade. The performance
of garage and driveway slabs-on-grade can be improved by over-excavating the
subgrade to match foundation recommendations. Costs could be substantial.
Over-excavation guidelines for foundations and interior slabs may be halved for
garage slabs and exterior flatwork, provided additional risk of movement and
cracking is acceptable in these areas. Backfill below slabs should be moisture
conditioned and compacted to reduce settlement, as discussed in BACKFILL
COMPACTION. Driveways and exterior slabs founded on the backfill may settle
and crack if the backfill is not properly moisture treated and compacted. Where
slabs-on-grade are used, we recommend adherence to the precautions for slab-
on-grade construction that are included in Exhibit A.
OVER-EXCAVATION
If you and the homebuyers are willing to accept risk of potential movements,
a slab-on-grade floor and spread footing foundations can be used if constructed
on an over-excavation. The over-excavation should extend below the slab and
foundation subgrade (per Figure 2) and at least 2 feet beyond the perimeter of the
footprint of the structure. The existing on-site soils are suitable for re-use as fill
material provided debris or deleterious organic materials are removed.
Areas to receive fill should be scarified, moisture-conditioned and
compacted to at least 95 percent of standard Proctor maximum dry density (ASTM
D 698, AASHTO T 99). Clay fill soils placed below the building should be moisture
conditioned between optimum and 3 percent above optimum moisture content.
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The fill should be moisture-conditioned, placed in thin, loose lifts (8 inches or less)
and compacted as described above. We should observe placement and test
compaction of fill during construction. Fill placement and compaction activities
should not be conducted when the fill material or subgrade is frozen.
BELOW-GRADE WALLS
Foundation walls and grade beams that extend below grade should be
designed for lateral earth pressures where backfill is not present to about the same
extent on both sides of the wall. Many factors affect the value of the design lateral
earth pressure. These factors include, but are not limited to, the type, compaction,
slope and drainage of the backfill, and the rigidity of the wall against rotation and
deflection. For a very rigid wall where negligible or very little deflection will occur,
an "at-rest" lateral earth pressure should be used in design. For walls that can
deflect or rotate 0.5 to 1 percent of the wall height (depending upon the backfill
types), lower "active" lateral earth pressures are appropriate. Our experience
indicates foundation walls can deflect or rotate slightly under normal design loads
and that this deflection results in satisfactory wall performance. Thus, the earth
pressure on the walls will likely be between the "active" and "at-rest" conditions.
If on-site soils are used as backfill and the backfill is not saturated, we
recommend design of foundation walls at this site using an equivalent fluid density
of at least 60 pounds per cubic foot (pcf). This value assumes deflection; some
minor cracking of walls may occur. If very little wall deflection is desired, higher
design density may be appropriate. The structural engineer should also consider
site-specific grade restrictions and the effects of large openings on the behavior of
the walls.
BACKFILL COMPACTION
Settlement of foundation wall and utility trench backfill can cause damage
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to concrete flatwork and/or result in poor drainage conditions. Compaction of
backfill can reduce settlement. Attempts to compact backfill near foundations to a
high degree can damage foundation walls and window wells and may increase
lateral pressures on the foundation walls. The potential for cracking of a foundation
wall can vary widely based on many factors including the degree of compaction
achieved, the weight and type of compaction equipment utilized, the structural
design of the wall, the strength of the concrete at the time of backfill compaction,
and the presence of temporary or permanent bracing.
Proper moisture conditioning of backfill is as important as compaction,
because settlement commonly occurs in response to wetting. The addition of
water complicates the backfill process, especially during cold weather. Frozen
soils are not considered suitable for use as backfill because excessive settlement
can result when the frozen materials thaw. Exhibit C describes four alternative
methods to place, moisture condition, and compact backfill along with a range of
possible settlements, and advantages and disadvantages of each approach, all
based upon our experience. These are just a few of the possible techniques, and
represent a range for your evaluation. We recommend Alternatives C or D if you
wish to control potential settlement.
Precautions should be taken when backfilling against a basement wall.
Temporary bracing of comparatively long, straight sections of foundation walls
should be used to limit damage to walls during the compaction process. Waiting at
least seven days after the walls are placed to allow the concrete to gain strength
can also reduce the risk of damage. Compaction of fill placed beneath and next to
window wells, counterforts, and grade beams may be difficult to achieve without
damaging these building elements. Proper moisture conditioning of the fill prior to
placement in these areas will help reduce potential settlement.
Ideally, drainage swales should not be located over the backfill zone
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(including excavation ramps), as this can increase the amount of water infiltration
into the backfill and cause excessive settlement. Swales should be designed to be
a minimum of at least 5 feet from the foundation to help reduce water infiltration.
Irrigated vegetation, sump pump discharge pipes, sprinkler valve boxes, and roof
downspout terminations should also be at least 5 feet from the foundation.
SUBSURFACE DRAINS AND SURFACE DRAINAGE
Water from surface irrigation of lawns and landscaping frequently flows
through relatively permeable backfill placed adjacent to a residence and collects
on the surface of less permeable soils occurring at the bottom of foundation
excavations. This process can cause wet or moist conditions in below grade areas
after construction. We understand no below-grade areas are planned with the
proposed construction. If plans change to include crawlspaces or basements, we
should be contacted to update our recommendations.
Our experience indicates moist conditions can develop in non-basement
crawl space areas resulting in isolated instances of damp soils, musty smells and,
in rare cases, standing water. Crawl space areas should be well ventilated,
depending on the use of a vapor retarder on the exposed soils and the floor
material selected. Perimeter drains for non-basement crawl space areas should
be installed as required by the 2018 IRC.
Proper design, construction and maintenance of surface drainage are
critical to the satisfactory performance of foundations, slabs-on-grade and other
improvements. Landscaping and irrigation practices will also affect performance.
Exhibit B contains our recommendations for surface drainage, irrigation and
maintenance.
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CONCRETE
Concrete that comes into contact with soils can be subject to sulfate attack.
We measured water-soluble sulfate concentrations in four samples from this site.
Concentrations were measured between below measurable limits (<0.01 percent)
and 0.20 percent. For this level of sulfate concentration, ACI 332-08 Code
Requirements for Residential Concrete indicates concrete shall be made with
ASTM C150 Type II cement, or an ASTM C595 or C1157 hydraulic cement
meeting moderate sulfate-resistant hydraulic cement (MS) designation.
Superficial damage may occur to the exposed surfaces of highly permeable
concrete. To control this risk and to resist freeze-thaw deterioration, the water-to-
cementitious materials ratio should not exceed 0.50 for concrete in contact with
soils that are likely to stay moist due to surface drainage or high water tables.
Concrete should have a total air content of 6 percent ± 1.5 percent. We advocate
all foundation walls and grade beams in contact with the soils (including the inside
and outside faces of garage and crawl space grade beams) be damp-proofed.
EXCAVATIONS
Excavations made at this site, including those for foundations and utilities,
may be governed by local, state, or federal guidelines or regulations.
Subcontractors should be familiar with these regulations and take whatever
precautions they deem necessary to comply with the requirements and thereby
protect the safety of their employees and that of the general public. Some of the
soils are soft and will be displaced if wheeled equipment is used in the excavations.
To minimize soil disturbance, we recommend wheeled traffic not be allowed in the
excavations.
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CONSTRUCTION OBSERVATIONS
We recommend that CTL | Thompson, Inc. provide construction observation
services to allow us the opportunity to verify whether soil conditions are consistent
with those found during this investigation. Other observations are recommended
to review general conformance with design plans. If others perform these
observations, they must accept responsibility to judge whether the
recommendations in this report remain appropriate.
GEOTECHNICAL RISK
The concept of risk is an important aspect with any geotechnical evaluation
primarily because the methods used to develop geotechnical recommendations do
not comprise an exact science. We never have complete knowledge of subsurface
conditions. Our analysis must be tempered with engineering judgment and
experience. Therefore, the recommendations presented in any geotechnical
evaluation should not be considered risk-free. Our recommendations represent our
judgment of those measures that are necessary to increase the chances that the
structures will perform satisfactorily. It is critical that all recommendations in this
report are followed during construction. Homeowners must assume responsibility
for maintaining the structures and use appropriate practices regarding drainage
and landscaping. Improvements performed by homeowners after construction,
such as finishing a basement or construction of additions, retaining walls, decks,
patios, landscaping and exterior flatwork, should be completed in accordance with
recommendations in this report.
LIMITATIONS
This report has been prepared for the exclusive use of TWG Development,
LLC for the purpose of providing geotechnical design and construction criteria for
the proposed project. The information, conclusions, and recommendations
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17
presented herein are based upon consideration of many factors including, but not
limited to, the type of structures proposed, the geologic setting, and the subsurface
conditions encountered. The conclusions and recommendations contained in the
report are not valid for use by others. Standards of practice evolve in the area of
geotechnical engineering. The recommendations provided are appropriate for
about three years. If the proposed residences are not constructed within about
three years, we should be contacted to determine if we should update this report.
Sixteen borings were drilled across the site during this investigation to
obtain a reasonably accurate picture of the subsurface conditions. Variations in
the subsurface conditions not indicated by our borings are possible. A
representative of our firm should observe foundation excavations to confirm the
exposed materials are as anticipated from our borings. We should also test
compaction of fill where over-excavation is used.
We believe this investigation was conducted with that level of skill and care
ordinarily used by geotechnical engineers practicing in this area at this time. No
warranty, express or implied, is made. If we can be of further service in discussing
the contents of this report or in the analysis of the influence of subsurface
conditions on design of the structures, please call.
CTLTHOMPSON, INC.
Taylor H. Ray, EI R.B. “Chip” Leadbetter, III, PE
Staff Geotechnical Engineer Senior Geotechnical Engineer
THR:RBL
TH-1
TBM
TH-2
TH-3 TH-4
TH-5
TH-6
Kechter Road
TH-101 TH-102
TH-103
TH-104
TH-105
TH-106
TH-107
TH-108
TH-109
TH-110
TH-111
TH-112
TH-113
TH-114
TH-115
TH-116 LADY MOON DR.STRAUSS CABIN RD.KECHTER RD.
SITE
ROCK CREEK DR.
LEGEND:
INDICATES APPROXIMATE
LOCATION OF EXPLORATORY
BORING
INDICATES APPROXIMATE
LOCATION OF TEMPORARY
BENCHMARK; BACK OF WALK
(ESTIMATED ELEVATION PER
TOPO SURVEY = 4898.5')
INDICATES APPROXIMATE
LOCATION OF EXPLORATORY
BORING FROM PRELIMINARY
INVESTIGATION
TH-101
(10.6)
TBM
TH-1
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL I T PROJECT NO. FC08892.001-120
FIGURE 1
Locations of
Exploratory
Borings
VICINITY MAP
(FORT COLLINS, COLORADO)
NOT TO SCALE
80'40'
APPROXIMATE
SCALE: 1" = 80'
0'
Kechter Road LADY MOON DR.STRAUSS CABIN RD.KECHTER RD.
SITE
ROCK CREEK DR.
LEGEND:
INDICATES 4'
OVER-EXCAVATION
INDICATES 6'
OVER-EXCAVATION
INDICATES 8'
OVER-EXCAVATION
VICINITY MAP
(FORT COLLINS, COLORADO)
NOT TO SCALE
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL I T PROJECT NO. FC08892.001-120 FIGURE 2
Over-Excavation
Recommendations
80'40'
APPROXIMATE
SCALE: 1" = 80'
0'
APPENDIX A
SUMMARY LOGS OF EXPLORATORY BORINGS
4,865
4,870
4,875
4,880
4,885
4,890
4,895
4,900
4,905
4,865
4,870
4,875
4,880
4,885
4,890
4,895
4,900
4,905
30/12
34/12
47/12
18/12
12/12
WC=11.3DD=112LL=31 PI=15-200=84
WC=9.4DD=129SW=7.7
WC=16.5SW=2.5
WC=11.3DD=112LL=31 PI=15-200=84
WC=9.4DD=129SW=7.7
WC=16.5SW=2.5
TH-101
El. 4902.0
Prop. FG 4904.0
14/12
21/12
8/12
8/12
14/12
WC=5.8DD=110SW=-1.0SS=<0.01
WC=16.4DD=114SW=3.4
WC=5.8DD=110SW=-1.0SS=<0.01
WC=16.4DD=114SW=3.4
TH-102
El. 4902.3
Prop. FG 4904.0
32/12
20/12
24/12
14/12
13/12
WC=11.9DD=111SW=11.0
WC=10.8DD=121SW=2.3
WC=11.9DD=111SW=11.0
WC=10.8DD=121SW=2.3
TH-103
El. 4902.3
Prop. FG 4903.0
19/12
24/12
11/12
7/12
WC=10.0DD=102SW=2.2
WC=10.0DD=102SW=2.2
TH-104
El. 4902.5
Prop. FG 4903.0
13/12
18/12
10/12
15/12
11/12
WC=10.5DD=119SW=1.3SS=<0.01
WC=10.5DD=119SW=1.3SS=<0.01
TH-105
El. 4902.5
Prop. FG 4901.0
ELEVATION - FEETFIGURE A- 1ELEVATION - FEETSummary Logs of
Exploratory Borings
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
4,865
4,870
4,875
4,880
4,885
4,890
4,895
4,900
4,905
4,865
4,870
4,875
4,880
4,885
4,890
4,895
4,900
4,905
13/12
11/12
8/12
24/12
WC=9.1-200=68
WC=21.9DD=94SW=-0.9
WC=9.1-200=68
WC=21.9DD=94SW=-0.9
TH-106
El. 4903.0
Prop. FG 4901.0
21/12
6/12
11/12
28/12
WC=9.4DD=119SW=5.3
WC=15.3DD=110SW=0.4
WC=9.4DD=119SW=5.3
WC=15.3DD=110SW=0.4
TH-107
El. 4903.0
Prop. FG 4901.0
15/12
22/12
16/12
15/12
14/12
WC=11.5DD=117SW=4.3
WC=11.5DD=117SW=4.3
TH-108
El. 4902.8
Prop. FG 4901.0
27/12
24/12
16/12
19/12
WC=13.2DD=102SW=4.9
WC=13.4DD=117SW=1.1
WC=13.2DD=102SW=4.9
WC=13.4DD=117SW=1.1
TH-109
El. 4902.3
Prop. FG 4902.0
19/12
16/12
19/12
10/12
13/12
WC=10.9DD=110SW=4.4
WC=14.2DD=113SW=2.6
WC=10.9DD=110SW=4.4
WC=14.2DD=113SW=2.6
TH-110
El. 4901.8
Prop. FG 4902.0
ELEVATION - FEETFIGURE A- 2ELEVATION - FEETSummary Logs of
Exploratory Borings
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
4,860
4,865
4,870
4,875
4,880
4,885
4,890
4,895
4,900
4,905
4,860
4,865
4,870
4,875
4,880
4,885
4,890
4,895
4,900
4,905
10/12
17/12
16/12
16/12
WC=10.4DD=90SW=0.7SS=<0.01
WC=11.8DD=118SW=0.4
WC=10.4DD=90SW=0.7SS=<0.01
WC=11.8DD=118SW=0.4
TH-111
El. 4902.5
Prop. FG 4902.0
17/12
9/12
8/12
14/12
13/12
WC=10.5SW=5.4-200=74
WC=10.5SW=5.4-200=74
TH-112
El. 4903.3
Prop. FG 4901.0
8/12
4/12
8/12
50/9
WC=13.6DD=111SW=1.1
WC=13.6DD=111SW=1.1
TH-113
El. 4902.5
Prop. FG 4900.0
15/12
12/12
27/12
12/12
14/12
WC=11.6DD=115SW=2.8SS=0.200
WC=13.0DD=118SW=0.6
WC=11.6DD=115SW=2.8SS=0.200
WC=13.0DD=118SW=0.6
TH-114
El. 4898.5
Prop. FG 4899.0
10/12
13/12
13/12
10/12
19/12
WC=12.8DD=107SW=3.3
WC=7.2DD=93SW=2.2LL=19 PI=0-200=85
WC=12.8DD=107SW=3.3
TH-115
El. 4902.3
Prop. FG 4901.0
15/12
9/12
5/12
16/12
13/12
WC=10.2DD=118SW=5.8
WC=15.2DD=116SW=0.5
WC=10.2DD=118SW=5.8
WC=15.2DD=116SW=0.5
TH-116
El. 4902.5
Prop. FG 4902.0
ELEVATION - FEETFIGURE A- 3
DRIVE SAMPLE. THE SYMBOL 10/12 INDICATES 10 BLOWS OF A 140-POUND HAMMER FALLING
30 INCHES WERE REQUIRED TO DRIVE A 2.5-INCH O.D. SAMPLER 12 INCHES.ELEVATION - FEETWATER LEVEL MEASURED SEVERAL DAYS AFTER DRILLING.
SILT, CLAYEY, SANDY, SLIGHTLY MOIST TO MOIST, LIGHT BROWN, TAN, (ML)
2.
3.
CLAY, SILTY, SANDY, MOIST, STIFF TO VERY STIFF, BROWN, OLIVE (CL)
THE BORINGS WERE DRILLED FEBRUARY 2021 USING 4-INCH DIAMETER CONTINUOUS-FLIGHT
AUGERS AND A TRUCK-MOUNTED DRILL RIG.
1.
LEGEND:
NOTES:
SAND AND GRAVEL, CLEAN TO CLAYEY, MOIST TO WET, MEDIUM DENSE, BROWN, REDDISH
BROWN (SP, GP, GC, SC)
WATER LEVEL MEASURED AT TIME OF DRILLING.
BORING ELEVATIONS WERE SURVEYED BY A REPRESENTATIVE OF OUR FIRM REFERENCING
THE TEMPORARY BENCHMARK SHOWN ON FIGURE 1.
THESE LOGS ARE SUBJECT TO THE EXPLANATIONS, LIMITATIONS AND CONCLUSIONS IN THIS
REPORT.
4.
Summary Logs of
Exploratory Borings
WC
DD
SW
-200
LL
PI
UC
SS
-
-
-
-
-
-
-
-
INDICATES APPROXIMATE PROPOSED FINAL GRADE.
INDICATES MOISTURE CONTENT (%).
INDICATES DRY DENSITY (PCF).
INDICATES SWELL WHEN WETTED UNDER OVERBURDEN PRESSURE (%).
INDICATES PASSING NO. 200 SIEVE (%).
INDICATES LIQUID LIMIT.
INDICATES PLASTICITY INDEX.
INDICATES UNCONFINED COMPRESSIVE STRENGTH (PSF).
INDICATES SOLUBLE SULFATE CONTENT (%).
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
SAND, CLEAN TO CLAYEY, MOIST TO WET, MEDIUM DENSE, BROWN, REDDISH BROWN (SP, SC)
APPENDIX B
RESULTS OF LABORATORY TESTS
TABLE B-1 – SUMMARY OF LABORATORY TESTING
TABLE B-2 – GROUND HEAVE ESTIMATES
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=129 PCF
From TH - 101 AT 4 FEET MOISTURE CONTENT=9.4 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-1
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=PCF
From TH - 101 AT 9 FEET MOISTURE CONTENT=16.5 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-2
Sample of SAND, CLAYEY, GRAVELLY (SC) DRY UNIT WEIGHT=110 PCF
From TH - 102 AT 4 FEET MOISTURE CONTENT=5.8 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
ADDITIONAL COMPRESSION UNDER
CONSTANT PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-3
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=114 PCF
From TH - 102 AT 9 FEET MOISTURE CONTENT=16.4 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-4
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=111 PCF
From TH - 103 AT 2 FEET MOISTURE CONTENT=11.9 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-5
Sample of SAND, CLAYEY (SC) DRY UNIT WEIGHT=121 PCF
From TH - 103 AT 9 FEET MOISTURE CONTENT=10.8 %
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=102 PCF
From TH - 104 AT 4 FEET MOISTURE CONTENT=10.0 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONCOMPRESSION % EXPANSION-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
0.1 1.0 10 100
Swell Consolidation
Test Results FIGURE B-6
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=119 PCF
From TH - 105 AT 9 FEET MOISTURE CONTENT=10.5 %
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=94 PCF
From TH - 106 AT 9 FEET MOISTURE CONTENT=21.9 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONCOMPRESSION % EXPANSION-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-4
-3
-2
-1
0
1
2
3
ADDITIONAL COMPRESSION UNDER
CONSTANT PRESSURE DUE TO
WETTING
0.1 1.0 10 100
0.1 1.0 10 100
Swell Consolidation
Test Results FIGURE B-7
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=119 PCF
From TH - 107 AT 4 FEET MOISTURE CONTENT=9.4 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-8
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=110 PCF
From TH - 107 AT 9 FEET MOISTURE CONTENT=15.3 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-9
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=117 PCF
From TH - 108 AT 4 FEET MOISTURE CONTENT=11.5 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-10
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=102 PCF
From TH - 109 AT 2 FEET MOISTURE CONTENT=13.2 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-11
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=117 PCF
From TH - 109 AT 9 FEET MOISTURE CONTENT=13.4 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-12
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=110 PCF
From TH - 110 AT 4 FEET MOISTURE CONTENT=10.9 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-13
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=113 PCF
From TH - 110 AT 9 FEET MOISTURE CONTENT=14.2 %
Sample of SILT, CLAYEY, SANDY (ML) DRY UNIT WEIGHT=90 PCF
From TH - 111 AT 4 FEET MOISTURE CONTENT=10.4 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONCOMPRESSION % EXPANSION-3
-2
-1
0
1
2
3
4
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
0.1 1.0 10 100
Swell Consolidation
Test Results FIGURE B-14
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=118 PCF
From TH - 111 AT 9 FEET MOISTURE CONTENT=11.8 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-15
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=PCF
From TH - 112 AT 4 FEET MOISTURE CONTENT=%
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-16
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=111 PCF
From TH - 113 AT 2 FEET MOISTURE CONTENT=13.6 %
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=115 PCF
From TH - 114 AT 2 FEET MOISTURE CONTENT=11.6 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONCOMPRESSION % EXPANSION-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-3
-2
-1
0
1
2
3
4
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
0.1 1.0 10 100
Swell Consolidation
Test Results FIGURE B-17
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=118 PCF
From TH - 114 AT 9 FEET MOISTURE CONTENT=13.0 %
Sample of SILT, CLAYEY, SANDY (ML) DRY UNIT WEIGHT=93 PCF
From TH - 115 AT 2 FEET MOISTURE CONTENT=7.2 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSF
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSIONCOMPRESSION % EXPANSION-4
-3
-2
-1
0
1
2
3
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
-3
-2
-1
0
1
2
3
4
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
0.1 1.0 10 100
Swell Consolidation
Test Results FIGURE B-18
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=107 PCF
From TH - 115 AT 4 FEET MOISTURE CONTENT=12.8 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-19
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=118 PCF
From TH - 116 AT 4 FEET MOISTURE CONTENT=10.2 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-20
Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=116 PCF
From TH - 116 AT 9 FEET MOISTURE CONTENT=15.2 %
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTL | T PROJECT NO. FC08892.001-120
APPLIED PRESSURE -KSFCOMPRESSION % EXPANSION-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
EXPANSION UNDER CONSTANT
PRESSURE DUE TO WETTING
0.1 1.0 10 100
Swell Consolidation
Test Results
FIGURE B-21
PASSINGWATER-MOISTUREDRYLIQUIDPLASTICITYAPPLIEDSWELLNO. 200SOLUBLEDEPTHCONTENTDENSITYLIMITINDEXSWELL*PRESSUREPRESSURESIEVESULFATESBORING(FEET)(%)(PCF)(%)(PSF)(PSF)(%)(%)DESCRIPTIONTH-101211.3112311584CLAY, SANDY (CL)TH-10149.41297.7500CLAY, SANDY (CL)TH-101916.52.51,100CLAY, SANDY (CL)TH-10245.8110-1.0500<0.01SAND, CLAYEY, GRAVELLY (SC)TH-102916.41143.41,100CLAY, SANDY (CL)TH-103211.911111.0200CLAY, SANDY (CL)TH-103910.81212.31,100SAND, CLAYEY (SC)TH-104410.01022.25001,700CLAY, SANDY (CL)TH-105910.51191.31,100<0.01CLAY, SANDY (CL)TH-10649.168CLAY, SANDY (CL)TH-106921.994-0.91,100CLAY, SANDY (CL)TH-10749.41195.35008,500CLAY, SANDY (CL)TH-107915.31100.41,100CLAY, SANDY (CL)TH-108411.51174.3500CLAY, SANDY (CL)TH-109213.21024.9200CLAY, SANDY (CL)TH-109913.41171.11,100CLAY, SANDY (CL)TH-110410.91104.45005,400CLAY, SANDY (CL)TH-110914.21132.61,100CLAY, SANDY (CL)TH-111410.4900.7500900<0.01SILT, CLAYEY, SANDY (ML)TH-111911.81180.41,100CLAY, SANDY (CL)TH-112410.55.450074CLAY, SANDY (CL)TH-113213.61111.1200CLAY, SANDY (CL)TH-114211.61152.82000.20CLAY, SANDY (CL)TH-114913.01180.61,100CLAY, SANDY (CL)TH-11527.2931902.220085SILT, CLAYEY, SANDY (ML)TH-115412.81073.35003,700CLAY, SANDY (CL)TH-116410.21185.8500CLAY, SANDY (CL)TH-116915.21160.51,100CLAY, SANDY (CL)SWELL TEST RESULTS*TABLE B-ISUMMARY OF LABORATORY TESTINGATTERBERG LIMITSPage 1 of 1* NEGATIVE VALUE INDICATES COMPRESSION.TWG DEVELOPMENT, LLC3620 EAST KECHTER ROAD TOWNHOMESCTL|T PROJECT NO. FC08892.001-120
TWG DEVELOMPENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120 TABLE B-2
TABLE B-2
SUMMARY OF HEAVE ESTIMATES
Boring
Proposed
Overexcavation
Depth (ft)
Slab
Performance
Risk
Total Heave
Estimate (Inches)
Post Overexcavation
Remaining Heave
Estimate (Inches)
Ground
Surface
Frost
Depth
Ground
Surface
Frost
Depth
TH-101 8 High 5.3 5.1 2.2 1.3
TH-102 6 Moderate 2.3 2.2 1.6 1.3
TH-103 4 Moderate 4.5 2.9 1.8 1.2
TH-104 4 Moderate 3.9 2.1 1.0 0.5
TH-105 4 Low 2.3 1.4 0.9 0.4
TH-106 4 Low 2.3 1.2 0.7 0.2
TH-107 4 Low 2.2 1.1 0.6 0.1
TH-108 4 Moderate 2.8 1.8 1.3 0.8
TH-109 4 Moderate 2.9 1.9 1.3 0.6
TH-110 6 Moderate 3.7 2.8 1.5 0.8
TH-111 6 Low 2.5 1.5 0.4 0.1
TH-112 4 Moderate 3.1 2.0 1.4 0.7
TH-113 4 Low 2.1 1.3 0.9 0.4
TH-114 4 Low 1.3 0.9 0.6 0.3
TH-115 4 Low 1.8 1.2 0.9 0.4
TH-116 6 Low 3.2 2.0 0.5 0.1
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120
EXHIBIT A-1
EXHIBIT A
SLAB PERFORMANCE RISK EVALUATION,
INSTALLATION AND MAINTENANCE
As part of our evaluation of the subsoils and bedrock, samples were tested in the
laboratory using a swell test. In the test procedure, a relatively undisturbed sample
obtained during drilling is first loaded and then flooded with water and allowed to swell.
The pressure applied prior to wetting can approximate the weight of soil above the sample
depth or be some standard load. The measured percent swell is not the sole criteria in
assessing potential movement of slabs-on-grade and the risk of poor slab performance.
The results of a swell test on an individual lot are tempered with data from surrounding
lots, depth of tests, depth of excavation, soil profile, and other tests. This judgment has
been described by the Colorado Association of Geotechnical Engineers (CAGE, 1996) as
it relates to basement slab-on-grade floors. It can also be used to help judge performance
risk for other slabs-on-grade such as garage floors, driveways, and sidewalks. CTL
Thompson also performs potential heave calculations to aid in our judgment. The risk
evaluation is considered when we evaluate appropriate foundation systems for a given
site. In general, more conservative foundation designs are used for higher risk sites to
control the likelihood of excessive foundation movement.
As a result of the Slab Performance Risk Evaluation, sites are categorized as low,
moderate, high, or very high risk. This is a judgment of the swelling characteristics of the
soils and bedrock likely to influence slab performance.
REPRESENTATIVE MEASURED SWELL AND CORRESPONDING SLAB
PERFORMANCE RISK CATEGORIES
Slab Performance
Risk Category
Representative Percent Swell*
(500 psf Surcharge)
Representative Percent Swell*
(1000 psf Surcharge)
Low 0 to <3 0 to <2
Moderate 3 to <5 2 to <4
High 5 to <8 4 to <6
Very High > 8 > 6
*Note: The representative percent swell values presented are not necessarily measured values; rather,
they are a judgment of the swelling characteristics of the soil and bedrock likely to influence slab
performance.
The rating of slab performance risk on a site as low or high is not absolute. Rather,
this rating represents a judgment. Movement of slabs may occur with time in low,
moderate, high, and very high risk areas as the expansive soils respond to increases in
moisture content. Overall, the severity and frequency of slab damage usually is greater in
high and very high rated areas. Heave of slabs-on-grade of 3 to 5 inches is not uncommon
in areas rated as high or very high risk. On low and moderate risk sites, slab heave of 1
to 2 inches is considered normal and we believe in the majority of instances, movements
of this magnitude constitute reasonable slab performance; more heave can occur. Slabs
can be affected on all sites. On lots rated as high or very high risk, there is more likelihood
of need to repair, maintain or replace basement and garage floors and exterior flatwork.
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120
EXHIBIT A-2
CTL | Thompson, Inc. recommends use of structurally supported basement floors,
known as “structural floors,” for lots rated as high and very high risk. We also recommend
use of structural basement floors on walkout and garden level lots rated as moderate, high
or very high risk. If home buyers cannot tolerate movement of a slab-on-grade basement
floor, they should select a lot where a structurally supported floor will be constructed or
request that a structurally supported floor be installed.
The home buyer should be advised the floor slab in the basement may move and
crack due to heave or settlement and that there may be maintenance costs associated
during and after the builder warranty period. A buyer who chooses to finish a basement
area must accept the risk of slab heave, cracking and consequential damages. Heave or
settlement may require maintenance of finish details to control damage. Our experience
suggests that soil moisture increases below residence sites due to covering the ground
with the house and exterior flatwork, coupled with the introduction of landscape irrigation.
In most cases, slab movements (if any) resulting from this change occur within three to
five years. We suggest delaying finish in basements with slab-on-grade floors until at least
three years after start of irrigation. It is possible basement floor slab and finish work
performance will be satisfactory if a basement is finished earlier, particularly on low risk
sites.
For portions of the houses where conventional slabs-on-grade are used, we
recommend the following precautions. These measures will not keep slabs-on-grade from
heaving; they tend to mitigate damages due to slab heave.
1. Slab-on-grade floor construction should be limited to areas such as
garages and basements where slab movement and cracking are
acceptable to the builder and home buyer.
2. The 2006, 2009, 2012, 2015 and 2018 International Residential Code (IRC
R506) states that a 4-inch base course layer consisting of clean graded
sand, gravel, crushed stone or crushed blast furnace slag shall be placed
beneath below grade floors (unless the underlying soils are free-draining),
along with a vapor retarder. Installation of the base course and vapor
retarder is not common in this area. Historically, there has been some
concern that installation of clean base course could allow wetting of
expansive soils to spread from an isolated source.
IRC states that the vapor retarder can be omitted where approved by the
building official. The merits of installation of a vapor retarder below floor
slabs depend on the sensitivity of floor coverings and building use to
moisture. A properly installed vapor retarder is more beneficial below
concrete slab-on-grade floors where floor coverings, painted floor surfaces,
or products stored on the floor will be sensitive to moisture. The vapor
retarder is most effective when concrete is placed directly on top of it, rather
than placing a sand or gravel leveling course between the vapor retarder
and the floor slab. Placement of concrete on the vapor retarder may
increase the risk of shrinkage cracking and curling. Use of concrete with
reduced shrinkage characteristics including minimized water content,
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120
EXHIBIT A-3
maximized coarse aggregate content, and reasonably low slump will
reduce the risk of shrinkage cracking and curling. Considerations and
recommendations for the installation of vapor retarders below concrete
slabs are outlined in Section 3.2.3 of the 2006 American Concrete Institute
(ACI) Committee 302, “Guide for Concrete Floor and Slab Construction
(ACI 302.R-96)”.
3. Conventional slabs should be separated from exterior walls and interior
bearing members with a slip joint that allows free vertical movement of the
slabs. These joints must be maintained by the home buyer to avoid transfer
of movement.
4. Underslab plumbing should be thoroughly pressure tested during
construction for leaks and be provided with flexible couplings. Gas and
waterlines leading to slab-supported appliances should be constructed with
flexibility. The homebuyer must maintain these connections.
5. Use of slab bearing partitions should be minimized. Where such partitions
are necessary, a slip joint (or float) allowing at least 2 inches of free vertical
slab movement should be used. Doorways should also be designed to
allow vertical movement of slabs. To limit damage in the event of
movement, sheetrock should not extend to the floor. The home buyer
should monitor partition voids and other connections and re-establish the
voids before they close to less than 1/2-inch.
6. Plumbing and utilities that pass through slabs should be isolated from the
slabs. Heating and air conditioning systems constructed on slabs should
be provided with flexible connections capable of at least 2 inches of vertical
movement so slab movement is not transmitted to the ductwork. These
connections must be maintained by the home buyer.
7. Roofs that overhang a patio or porch should be constructed on the same
foundation as the residence. Isolated piers or pads may be installed
beneath a roof overhang provided the slab is independent of the foundation
elements. Patio or porch roof columns may be positioned on the slab,
directly above the foundation system, provided the slab is structural and
supported by the foundation system. Structural porch or patio slabs should
be constructed to reduce the likelihood that settlement or heave will affect
the slab by placing loose backfill under the structurally supported slab or
constructing the slab over void-forming materials.
8. Patio and porch slabs without roofs and other exterior flatwork should be
isolated from the foundation. Movements of slabs should not be transmitted
to the foundation. Decks are more flexible and more easily adjusted in the
event of movement.
9. Frequent control joints should be provided in conventional slabs-on-grade
to reduce problems associated with shrinkage cracking and curling. Panels
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120
EXHIBIT A-4
that are approximately square generally perform better than rectangular
areas. We suggest an additional joint about 3 feet away from and parallel
to foundation walls.
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120
EXHIBIT B-1
EXHIBIT B
SURFACE DRAINAGE,
IRRIGATION AND MAINTENANCE
Performance of foundations and concrete flatwork is influenced by the
moisture conditions existing within the foundation soils. Surface drainage should
be designed to provide rapid runoff of surface water away from proposed
residences. Proper surface drainage and irrigation practices can help control the
amount of surface water that penetrates to foundation levels and contributes to
settlement or heave of soils and bedrock that support foundations and slabs-on-
grade. Positive drainage away from the foundation and avoidance of irrigation near
the foundation also help to avoid excessive wetting of backfill soils, which can lead
to increased backfill settlement and possibly to higher lateral earth pressures, due
to increased weight and reduced strength of the backfill. CTL | Thompson, Inc.
recommends the following precautions. The homebuyer should maintain surface
drainage and, if an irrigation system is installed, it should substantially conform to
these recommendations.
1. Wetting or drying of the open foundation excavations should be
avoided.
2. Excessive wetting of foundation soils before, during and after
construction can cause heave or softening of foundation soils and
result in foundation and slab movements. Proper surface drainage
around the residence and between lots is critical to control wetting.
3. The ground surface surrounding the exterior of each residence
should be sloped to drain away from the building in all directions. We
recommend a minimum constructed slope of at least 12 inches in the
first 10 feet (10 percent) in landscaped areas around each residence,
where practical. The recommended slope is for the soil surface
slope, not surface of landscaping rock.
4. We do not view the recommendation to provide a 10 percent slope
away from the foundation as an absolute. It is desirable to create this
slope where practical, because we know that backfill will likely settle
to some degree. By starting with sufficient slope, positive drainage
can be maintained for most settlement conditions. There are many
situations around a residence where a 10 percent slope cannot be
achieved practically, such as around patios, at inside foundation
corners, and between a house and nearby sidewalk. In these areas,
we believe it is desirable to establish as much slope as practical and
to avoid irrigation. We believe it is acceptable to use a slope on the
order of 5 percent perpendicular to the foundation in these limited
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120
EXHIBIT B-2
areas.
5. For lots graded to direct drainage from the rear yard to the front, it is
difficult to achieve 10 percent slope at the high point behind the
house. We believe it is acceptable to use a slope of about 6 inches
in the first 10 feet (5 percent) at this location.
6. Between houses that are separated by a distance of less than 20
feet, the constructed slope should generally be at least 10 percent to
the swale used to convey water out of this area. For lots that are
graded to drain to the front and back, we believe it is acceptable to
install a slope of 5 to 8 percent at the high point (aka “break point”)
between houses.
7. Construction of retaining walls and decks adjacent to the residence
should not alter the recommended slopes and surface drainage
around the residence. The ground surface under decks should be
compacted and slope away from the residence. 10-mil plastic
sheeting and landscaping rock may be placed under decks to soil
erosion and/or formation of depressions under the deck. The plastic
sheeting should direct water away from the residence. Retaining
walls should not flatten the surface drainage around the residence or
impede surface runoff.
8. Swales used to convey water across yards and between houses
should be sloped so that water moves quickly and does not pond for
extended periods of time. We suggest minimum slopes of about 2 to
2.5 percent in grassed areas and about 2 percent where landscaping
rock or other materials are present. If slopes less than about 2
percent are necessary, concrete-lined channels or plastic pipe
should be used. Fence posts, trees, and retaining walls should not
impede runoff in the swales.
9. Backfill around the foundation walls should be moistened and
compacted.
10. Roof downspouts and drains should discharge well beyond the limits
of all backfill. Splash blocks and/or extensions should be provided at
all downspouts so water discharges onto the ground beyond the
backfill. We generally recommend against burial of downspout
discharge. Where it is necessary to bury downspout discharge, solid,
rigid pipe should be used and it should slope to an open gravity
outlet. Downspout extensions, splash blocks and buried outlets must
be maintained by the homeowner.
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120
EXHIBIT B-3
11. The importance of proper irrigation and drainage practices and
maintenance cannot be over-emphasized. Irrigation should be
limited to the minimum amount sufficient to maintain vegetation;
application of more water will increase likelihood of slab and
foundation movements. Landscaping should be carefully designed
and maintained to minimize irrigation. Plants placed close to
foundations, particularly within 5 feet of the foundation, should be
limited to those with low moisture requirements and utilize only sub-
surface irrigation such as standard low volume drip emitters or in-line
drip irrigation. Irrigated grass, irrigation mainlines, above-surface
spray heads, rotors, and other above-surface irrigation spray devices
should not be located or discharge above the ground surface within
5 feet of the foundation
12. Plastic sheeting should not be placed beneath landscaped areas
adjacent to foundation walls or grade beams. Geotextile fabric will
inhibit weed growth yet still allow natural evaporation to occur.
TWG DEVELOPMENT, LLC
3620 EAST KECHTER ROAD TOWNHOMES
CTLT PROJECT NO. FC08892.001-120
EXHIBIT C-1
EXHIBIT C
EXAMPLE BACKFILL COMPACTION ALTERNATIVES
Alt. Description Possible
Settlement Pros (+) / Cons (-)
A
Place in 18 to 24-inch lifts,
without moisture conditioning.
Compact lift surface to about
85 percent of maximum
standard Proctor (ASTM
D698) dry density.
5 to 15
percent of
depth
(for 8 feet
of backfill,
5 to 15
inches)
+ Fast
+ Water not required
- Excessive Settlement
- Highest water penetration
- Highest probability of
warranty repair
B
Moisture condition within 2
percent of optimum, place in
12 to 18-inch lifts. Compact lift
surface to about 85 to 90
percent.
5 to 10
percent of
depth
+ Relatively Fast
- Moderate water penetration
- Excessive settlement
- Need for water
- Warranty repairs probable
C
Moisture condition to within 2
percent of optimum and place
in 8 to 12-inch lifts. Compact
lift surface to 90 to 95 percent.
2 to 5
percent of
depth
+ Reduced warranty
+ Reduced water infiltration
+ Reduced settlement
- Possible higher lateral pressure
- Slower
- Need for water
- Potential damage to walls
D
Moisture condition and place
as in C. Compact lift surface to
at least 95 percent
1 to 2
percent of
depth
+ Reduced warranty
+ Reduced water infiltration
+ Lowest comparative settlement
- Possible higher lateral pressure
- Slower
- Need for water
- Potential damage to walls