HomeMy WebLinkAbout215 MATHEWS OFFICE BUILDING - PDP - PDP150020 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTGEOTECHNICAL SUBSURFACE EXPLORATION REPORT
PROPOSED OFFICE BUILDING
215 MATTHEWS STREET
FORT COLLINS, COLORADO
Prepared By:
SOILOGIC, Inc.
Job Number: 15-1056
April 7, 2015
Soilogic, Inc.
3050 67th Avenue, Suite 200 Greeley, CO 80634 (970) 535-6144
P.O. Box 1121 Hayden, CO 81639 (970) 276-2087
April 7, 2015
Greg D. Fisher. Architect pllc
3115 Clyde Street
Fort Collins, Colorado 80524
Attn: Mr. Greg Fisher
Re: Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic Project # 15-1056
Mr. Fisher:
Soilogic, Inc. (Soilogic) personnel have completed the geotechnical subsurface exploration
you requested for the proposed office building to be constructed at 215 Matthews Street in
Fort Collins, Colorado. The results of our subsurface exploration and pertinent
geotechnical engineering recommendations are included with this report.
In general, the subsurface materials encountered in the completed site borings consisted of
light brown to reddish brown stiff to very stiff lean clay overlying dense to very dense sand
and gravel at depths ranging from approximately 8 to 11 feet below present site grade. The
lean clay was variable in moisture content and exhibited variable swell potential ranging
from none to low/moderate at in-situ moisture and density conditions. The sand and gravel
would be expected to exhibit no swell potential based on the materials physical properties
and engineering characteristics. The sand and gravel extended to the bottom of boring at a
depth of approximately 15 feet below present site grade.
Groundwater was encountered at a depth of approximately 13½ feet below ground surface
in boring B-1 at the time of drilling. Groundwater was not encountered at boring location
B-2 at that time. When checked approximately 24 hours after completion of drilling, A dry
cave-in was measured at depths of 12 and 13 feet below ground surface at boring locations
B-1 and B-2 respectively. Groundwater level information is indicated in the upper right
hand corner of the attached boring logs.
Due to the variable swell potential of the near-surface lean clay soils encountered at this
site and anticipated moderate foundation loads for the site structure, we recommend that
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street, Fort Collins, Colorado
Soilogic # 15-1056
2
overexcavation/backfill procedures be performed below the building footing foundations,
floor slabs and exterior flatwork in order to develop consistent and higher strength low-
volume-change (LVC) bearing/support conditions. Based on the subsurface conditions
encountered, results of laboratory testing and type of construction proposed, it is our
opinion the proposed office building could be constructed with conventional footing
foundations and floor slabs bearing on a mat of properly moisture-conditioned and
compacted overexcavation/backfill. Select granular fill materials are recommended for use
beneath building footing foundations whereas the site lean clay overburden soils could be
used as overexcavation/backfill beneath floor slabs and exterior flatwork. The
overexcavation/backfill procedures will help develop LVC-potential foundation bearing
and floor slab/exterior flatwork support reducing the potential for total and differential
movement of those supported elements subsequent to construction. The risk of some
movement cannot be eliminated. Due to the segmented nature of permeable pavements
and requirement for water infiltration, overexcavation/backfill procedures would not be
required in these areas with the understanding that some movement of the permeable
pavements will occur subsequent to construction. Other opinions and recommendations
concerning design criteria and construction details for the proposed site improvements are
included with this report.
We appreciate the opportunity to be of service to you on this project. If you have any
questions concerning the enclosed information or if we can provide any further assistance,
please do not hesitate to contact us.
Very Truly Yours,
Soilogic, Inc. Reviewed by:
Wolf von Carlowitz, P.E. Darrel DiCarlo, P.E.
Principal Engineer Senior Project Engineer
36746 44271
GEOTECHNICAL SUBSURFACE EXPLORATION REPORT
PROPOSED OFICE BUILDING
215 MATTHEWS STREET
FORT COLLINS, COLORADO
SOILOGIC # 15-1056
April 7, 2015
INTRODUCTION
This report contains the results of the completed geotechnical subsurface exploration for
the proposed office building to be constructed at 215 Matthews Street in Fort Collins,
Colorado. The purpose of our exploration was to describe the subsurface conditions
encountered in the completed site borings and develop the test data necessary to provide
recommendations concerning design and construction of the proposed building
foundation and support of floor slabs, exterior flatwork and site pavements. The
conclusions and recommendations outlined in this report are based on the results of the
completed field and laboratory testing and our experience with subsurface conditions in
this area.
PROPOSED CONSTRUCTION
Based on the provided site plan and our discussion with the project architect, we
understand the proposed office building will be a three (3) story combination structural
steel and wood frame structure constructed over a first floor parking area with a plan area
of approximately 4,300 square feet. Foundations loads for the structure are anticipated to
be light to moderate, with maximum continuous wall loads on the order of 6 kips per
lineal foot and individual column loads less than 120 kips. Permeable pavers are
anticipated to develop the wearing surface of the site drive and parking area pavements.
Small grade changes (on the order of 2 feet or less) are anticipated to develop finish site
grades in building and pavement areas.
SITE DESCRIPTION
The subject property is located at 215 Matthews Street in Fort Collins, Colorado. The lot
is currently occupied by a residence that we understand will be razed prior to construction
of the office building. The existing residence consists of a single-story wood-frame
structure that we expect is supported on some type of spread footing foundation and
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
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contains a partial basement area housing mechanical equipment. The remainder of the
site contains mature trees and associated landscape and flatwork improvements. The lot
is relatively flat, with the maximum difference in ground surface elevation across the
property estimated to be less than two (2) feet.
SITE EXPLORATION
Field Exploration
To develop subsurface information for the proposed site improvements, a total of two (2)
soil borings were completed on the lot to a depth of approximately 15 feet below present
site grade. In addition, three (3) shallow percolation test holes were drilled at each of the
boring locations to evaluate the suitability of the near-surface site soils to support
permeable pavement design. The boring locations were established in the field by
Soilogic, Inc. (Soilogic) personnel based on the accessibility of the site and overhead
constraints. A diagram indicating the approximate boring locations is included with this
report. Graphic logs of each of the auger borings are also included.
The test holes were advanced using 4-inch diameter continuous-flight auger, powered by
a truck-mounted CME-55 drill rig. Samples of the subsurface materials were obtained at
regular intervals using California barrel sampling procedures in general accordance with
ASTM specification D-1586. As part of the D-1586 sampling procedure, a standard
sampling barrel is driven into the substrata using a 140-pound hammer falling a distance
of 30 inches. The number of blows required to advance the sampler a distance of 12
inches is recorded and helpful in estimating the consistency, relative density or hardness
of the soils or bedrock encountered. In the California barrel sampling procedure, lesser
disturbed samples are obtained in removable brass liners. Samples of the subsurface
materials obtained in the field were sealed and returned to the laboratory for further
evaluation, classification and testing.
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
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Laboratory Testing
The samples collected were tested in the laboratory to measure natural moisture content
and visually or manually classified in accordance with the Unified Soil Classification
System (USCS). The USCS group symbols are indicated on the attached boring logs.
An outline of the USCS classification system is included with this report.
As part of the laboratory testing, a calibrated hand penetrometer (CHP) was used to
estimate the unconfined compressive strength of essentially cohesive specimens. The
CHP also provides a more reliable estimate of soil consistency than tactual observation
alone. Dry density, Atterberg limits, -200 wash and swell/consolidation tests were
completed on selected samples to help establish specific soil characteristics. Atterberg
limits tests are used to determine soil plasticity. The percent passing the #200 size sieve
(-200 wash test) is used to determine the percentage of fine grained soils (clay and silt) in
a sample. Swell/consolidation tests are performed to evaluate soil volume change
potential with variation in moisture content. Water Soluble Sulfates (WSS) tests were
also completed on two (2) selected soil samples to evaluate corrosive soil characteristics
with respect to buried concrete. The results of the completed laboratory tests are outlined
on the attached boring logs and swell/consolidation test summaries, or discussed
subsequently in this report.
SUBSURFACE CONDITIONS
Approximately 4 inches of vegetation and topsoil was encountered at the surface at
boring location B-1. Light brown to reddish brown lean clay with varying amounts of silt
and sand was encountered underlying the vegetative soil layer at boring location B-1 and
at the surface at boring location B-2. The near-surface lean clay varied from stiff to very
stiff in terms of consistency and exhibited variable moisture content and variable swell
potential (ranging from none to low/moderate) when inundated with water at a 500 psf
confining pressure. The lean clay extended to depths ranging from approximately 8 to 11
feet below ground surface and was underlain by reddish brown sand and gravel. The
sand and gravel varied from dense to very dense in terms of relative density, would be
expected to possess no to low swell potential based on the material’s physical properties
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
4
and engineering characteristics and extended to the bottom of both borings at a depth of
approximately 15 feet below present site grades.
The stratigraphy indicated on the included boring logs represents the approximate
location of changes in soil types. Actual changes may be more gradual than those
indicated.
Groundwater was encountered at a depth of approximately 13½ feet below ground
surface in boring B-1 at the time of drilling. Groundwater was not encountered at boring
location B-2 at that time. When checked approximately 24 hours after completion of
drilling, a dry cave-in was measured at depths of 12 and 13 feet below ground surface at
boring locations B-1 and B-2 respectively. Groundwater level information is indicated in
the upper right hand corner of the attached boring logs.
Groundwater levels will vary seasonally and over time based on weather conditions, site
development, irrigation practices and other hydrologic conditions. Perched and/or
trapped groundwater conditions may also be encountered at times throughout the year.
Perched water is commonly encountered in soils overlying less permeable soil layers
and/or bedrock. Trapped water is typically encountered within more permeable zones of
layered soil and bedrock systems. The location and amount of perched/trapped water can
also vary over time.
ANALYSIS AND RECOMMENDATIONS
General
The near-surface lean clay soils encountered at this site exhibited variable swell potential
ranging from none to low/moderate. Differential movement, including both settlement
and heaving of site improvements placed directly on or immediately above the variable
clay soils would be expected as building foundation loads are imposed and the moisture
content of those materials increases subsequent to construction.
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
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Based on the subsurface conditions encountered and results of laboratory testing, it is our
opinion overexcavation/backfill procedures could be completed beneath the building
footing foundations and floor slabs to reduce the potential for movement of those
supported elements subsequent to construction. Use of a select granular overexcavation/
backfill material will also allow for use of increased allowable soil bearing pressures in
foundation design. The risk of some movement cannot be eliminated. Recommendations
concerning overexcavation/backfill procedures to redevelop foundation and floor slab
support for the building are outlined below.
Drilled pier foundations could also be considered for support of the proposed building.
Drilled piers would anchor the building into site bedrock or be designed as friction piers,
significantly reducing the potential for movement of the structure subsequent to
construction. Due to the presence of essentially-granular soils and groundwater with
depth at this site, we expect casing of the drilled piers would be required for proper
construction. Deeper subsurface exploration would be required to determine the depth to
competent bedrock if drilled pier foundations will be utilized. If drilled pier foundations
are to be used, structural flooring systems or overexcavation/backfill procedures to
develop low volume change (LVC) floor slab subgrades would be required.
Recommendations concerning the design and construction of drilled pier foundations can
be provided at your request.
Foundation Bearing and Site Development
To develop higher allowable soil bearing capacities and low volume-change (LVC)
potential foundation and floor slab support, and reduce the potential for total and
differential movement of the building and building floor slab subsequent to construction,
we recommend a zone of properly placed and compacted fill be developed beneath those
supported elements. The LVC mat will provide a zone of material immediately beneath
the building foundation and floor slabs which will have low potential for volume change
subsequent to construction. The LVC mat and surcharge loads placed on the underlying
soils by the reconditioned mat would reduce the potential for total and differential
movement of the supported improvements subsequent to construction. The reconditioned
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
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zone would also assist in distributing movement in the event that some swelling of the
materials underlying the reconditioned zone occurs.
The overexcavation zone should extend to a depth of five (5) feet below proposed
foundation bearing and finished floor slab subgrade elevations. The overexcavation area
should extend a minimum of 8 inches laterally past the interior and exterior edges of the
footings for every 12 inches of overexcavation depth.
Since movement of exterior flatwork is generally less consequential than structural and
floor slab movement, it is our opinion the overexcavation zone beneath exterior flatwork
could be reduced to a minimum of 24 inches below finish subgrade level. With the
segmented nature of permeable pavements and ability of those systems to tolerate
movement without exhibiting distress and requirement for water infiltration, it is our
opinion overexcavation/backfill procedures in permeable pavement areas would not be
required. Some movement of the permeable pavement surface should be expected.
Soils used as overexcavation/backfill beneath footing foundations should consist of
essentially granular select fill free from organic matter, debris and other objectionable
materials. Based on results of the completed laboratory testing, it is our opinion the site
lean clay could be used as overexcavation beneath floor slabs and exterior flatwork
provided care is taken to develop the proper moisture content in those materials at the
time of placement and compaction.
We understand the existing residence and other associated site improvements will be
razed prior to construction of the new building. Within the new building, floor slab,
exterior flatwork and pavement areas, all existing foundations, floor slabs and other site
improvements should be completely removed. Care will be needed to ensure all in-place
fill/backfill materials associated with the existing site improvements are also completely
removed. In addition, all tree root systems and dry and desiccated soils associated with
the tree root systems should be completely removed from within the area of the proposed
building and beneath floor slabs, exterior flatwork and site pavements. The depth and
extent of required removal can best be established at the time of excavation through
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
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openhole observation. The excavated/removed materials should be replaced as controlled
and compacted fill as outlined below.
After stripping and completing all cuts and removal procedures and overexcavation as
described as outlined above and prior to placement of any new fill or flatwork concrete,
we recommend the exposed subgrade soils be scarified to a depth of 9 inches, adjusted in
moisture content and compacted to at least 95% of the material’s standard Proctor
maximum dry density. The moisture content of the scarified soils should be adjusted to
be within the range of ±2% of standard Proctor optimum moisture content at the time of
compaction. Scarification and compaction of the exposed subgrade soils in
overexcavation/backfill and permeable pavement areas would not be required.
Overexcavation/backfill for use beneath footing foundations should consist of a select
granular fill. Materials consistent with Colorado Department of Transportation (CDOT)
Class 7 Aggregate Base Course specifications could be considered for use as
overexcavation/backfill beneath footing foundations. Structural fill in foundation areas
should be placed in loose lifts not to exceed 9 inches thick, adjusted in moisture content
and compacted to at least 98% of the material’s standard Proctor maximum dry density.
The moisture content of structural fill soils should be adjusted to within the range of ±3%
of standard Proctor optimum moisture content at the time of placement and compactions.
General site fill, overexcavation/backfill and removal area backfill soils required to
develop the site should consist of approved, low-volume-change (LVC) soils free from
organic matter, debris and other objectionable materials. Based on results of the
completed laboratory testing, it is our opinion the site lean clay could be used as fill and
backfill in non-foundation bearing areas, provided the proper moisture content is
developed in those materials at the time of placement and compaction. Suitable fill and
backfill soils consisting of the site lean clay or similar soils should be placed in loose lifts
not to exceed 9 inches thick, adjusted to within ±2% of standard Proctor optimum
moisture content and compacted to at least 95% of the materials standard Proctor
maximum dry density.
Care should be taken to maintain the proper moisture content in the bearing/subgrade
soils prior to foundation and floor slab concrete placement and/or paving. The prepared
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
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structural mat should not be left exposed for extended periods of time. In the event that
the reconditioned soils are allowed to dry out or if rain, snowmelt or water from any
source is allowed to infiltrate the bearing/subgrade soils, reworking of those materials or
removal/replacement procedures may be required.
Inherent risks exist when building in areas of expansive soils. The overexcavation/
backfill procedures outlined above will reduce but not eliminate the potential for
movement of the building, building floor slabs, site pavements and exterior flatwork
subsequent to construction. The in-place materials below the moisture conditioned zone
can increase in moisture content causing movement of the overlying improvements.
Some limited movement of lightly-loaded building floor slabs, site pavements and
exterior flatwork should be expected.
Footing Foundations
For design of footing foundations bearing on a minimum of five (5) feet of select
granular fill compacted to at least 98% of the materials standard Proctor maximum dry
density, we recommend using a maximum net allowable soil bearing pressure of 2,500
psf.
Exterior footings should bear a minimum of 30 inches below finished adjacent exterior
grade to provide frost protection. We recommend formed strip footings have a minimum
width of 12 inches and isolated pad foundations have a minimum width of 24 inches in
order to facilitate construction and reduce the potential for development of eccentrically
loaded footings. Actual footing widths should be designed by a structural engineer.
For design of footing foundations and foundation walls to resist lateral movement, a
passive equivalent fluid pressure value of 350 pcf could be used. The top 30 inches of
subgrade could be considered a surcharge load but should not be used in the passive
resistance calculations. A coefficient of friction of 0.55 could be used between
foundation and floor slab concrete and the bearing/subgrade soils to resist sliding. The
recommended passive equivalent fluid pressure value and coefficient of friction do not
include a factor of safety.
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
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We estimate settlement of footing foundations supported on properly placed and
compacted structural fill developed as outlined above and resulting from the assumed
structural loads would be less than 1 inch. Differential settlement could approach the
amount of total settlement estimated above.
Seismicity
Based on the results of our exploration and our review of the International Building Code
(2003), a soil profile type D could be used for the site strata. Based on our review of
United States Geologic Survey (USGS) mapped information, design spectral response
acceleration values of SDS = .219 (21.9%) and S
D1 = .093 (9.3%) could be used.
Floor Slabs and Exterior Flatwork
The building floor slabs and exterior flatwork could be supported directly on the
overexcavation/backfill material placed and compacted as outlined above. A modulus of
subgrade reaction (k) value of 150 pci could be used for design of floor slabs supported
on overexcavation/backfill soils consisting of the on-site clay or similar soils. If select
granular fill will be used as overexcavation/backfill beneath floor slabs, a modulus of
subgrade reaction (k) value of 350 pci could be used for design. Disturbed subgrades or
subgrade materials that have been allowed to dry out or become wet and softened should
be removed and replaced or reconditioned in place prior to concrete placement.
As a precaution, we recommend all partition walls supported above at-grade floor slabs
be constructed as floating walls to help reduce the potential for differential slab to
foundation movement causing distress in upper sections of the building. A minimum 1½
inch void space is recommended. Special attention to stair systems, door framing,
drywall installation and trim carpentry should be taken to isolate those elements from the
floor slabs, allowing for some differential foundation to floor slab movement to occur
without transmitting stresses to the overlying structure.
Depending on the type of floor covering and floor covering adhesive used in finished slab
on ground areas, a vapor barrier may be required immediately beneath the floor slabs in
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
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order to maintain flooring product manufacturer warranties. A vapor barrier would help
reduce the transmission of moisture through the floor slabs. However, the unilateral
moisture release caused by placing concrete on an impermeable surface can increase slab
curl. The amount of slab curl can be reduced by careful selection of an appropriate
concrete mix. Slab curl cannot be eliminated. We recommend the owner, architect and
flooring contractor consider the performance of the slabs in conjunction with the
proposed flooring products to help determine if a vapor barrier will be required and
where best to position the vapor barrier in relation to the floor slab. Additional guidance
and recommendations concerning slab-on-grade design can be found in American
Concrete Institute (ACI) section 302.
Pavements Subgrades
At this time, we understand permeable pavements may be utilized for the site drive
and/or parking areas. Permeable pavement subgrades should be developed as outlined in
the “Foundation Bearing and Site Development” portion of this report. Care should be
taken to avoid densification of permeable pavement subgrade soils prior to placement of
the overlying system.
To complete the percolation test for aid in the design, three (3) eight-inch diameter and
36-inch deep percolation test holes were completed at each deep boring location. An
average percolation rate of 57 minutes per inch was established in the near surface site
soils and could be used in design.
With the recommended overexcavation/backfill procedures to develop finish foundation
bearing levels for the proposed building, it is our opinion a Partial of Full-Infiltration
section could be used for this site. The near surface site lean clay is fine graded, such that
a filter fabric should be employed at the clay/filter media interface.
Minimum light and heavy-duty structural permeable pavement section designs are
outlined below in Table I.
Geotechnical Subsurface Exploration Report
Proposed Office Building
215 Matthews Street
Fort Collins, Colorado
Soilogic # 15-1056
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Table I – Permeable Pavement Section Design
Classification
Roadway
Design Structural Number
Light-Duty
Private Drive/Parking
(2.42)
Heavy-Duty
Private Drive/Parking
(3.08)
Option A – Permeable Pavement
Surface Paver (SF Rima)
Storage Media
Filter Media
(Structural Number)
3.15” (0.40/inch)
*6” (0.11/inch)
6” (0.11/inch)
(2.58)
3.15” (0.40/inch)
*11” (0.11/inch)
6” (0.11/inch)
(3.13)
* The storage media thickness outlined above is from a structural support
perspective only for light-duty pavements. Greater thicknesses may be required
based on storage water calculations and minimum requirements provided by the
system manufacturer.
Light-duty pavements could be considered for light vehicle parking areas. Heavy-
duty pavements should be considered for access drives and other areas of the site
expected to receive heavy trash or delivery truck traffic. We recommend
permeable pavement filter and storage media be adjusted to a workable moisture
content and compacted to at least 75% of the material’s relative density.
Corrosive Soil Characteristics
Water-soluble sulfates (WSS) tests were completed on two (2) selected soil samples
obtained from the site to help evaluate corrosive soil characteristics with respect to buried
concrete. A corrosive soil characteristics outline is included with this report. The WSS
tests fall within the “negligible” and “moderate” classification with respect to the severity
of the sulfate environment. Type II cement should be used for project concrete exposed
to soils with a “moderate” classification. If Type II cement is not available, care should
be taken to thoroughly consolidate concrete exposed to the site soils. A maximum
water/cement ratio of 0.50 is recommended for “moderate” severity. In addition,
consideration could be given to utilizing air-entrained concrete exposed to the site soils,
Geotechnical Subsurface Exploration Report
Proposed Office Building
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Fort Collins, Colorado
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as this admixture will reduce the mix water/cement ratio and resulting concrete
permeability.
Drainage
Positive drainage is imperative for satisfactory long-term performance of the proposed
building and associated site improvements. We recommend positive drainage be
developed away from the structures during construction and maintained throughout the
life of the site improvements, with twelve (12) inches of fall in the first 10 feet away from
the building. Shallower slopes could be considered in hardscape areas. In the event that
some settlement of the building backfill soils occurs over time, the original grade and
associated positive drainage outlined above should be immediately restored.
Care should be taken in the planning of landscaping to avoid features which could result
in the fluctuation of the moisture content of the foundation bearing and flatwork and
pavement subgrade soils. We recommend watering systems be placed a minimum of 5
feet away from the perimeter of the site structure and be designed to discharge away from
all site improvements. Gutter systems should be considered to help reduce the potential
for water ponding adjacent to the structure, with the gutter downspouts, roof drains or
scuppers extended to discharge a minimum of 5 feet away from structural, flatwork and
pavement elements. Water which is allowed to pond adjacent to the site improvements
can result in unacceptable performance of those improvements over time.
LIMITATIONS
This report was prepared based upon the data obtained from the completed site
exploration, laboratory testing, engineering analysis and any other information discussed.
The completed borings provide an indication of subsurface conditions at the boring
locations only. Variations in subsurface conditions can occur in relatively short distances
away from the borings. This report does not reflect any variations which may occur
across the site or away from the borings. If variations in the subsurface conditions
anticipated become evident, the geotechnical engineer should be notified immediately so
that further evaluation and supplemental recommendations can be provided.
Geotechnical Subsurface Exploration Report
Proposed Office Building
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Fort Collins, Colorado
Soilogic # 15-1056
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The scope of services for this project does not include either specifically or by
implication any biological or environmental assessment of the site or identification or
prevention of pollutants or hazardous materials or conditions. Other studies should be
completed if concerns over the potential of such contamination or pollution exist.
The geotechnical engineer should be retained to review the plans and specifications so
that comments can be made regarding the interpretation and implementation of our
geotechnical recommendations in the design and specifications. The geotechnical
engineer should also be retained to provide testing and observation services during
construction to help determine that the design requirements are fulfilled.
This report has been prepared for the exclusive use of our client for specific application
to the project discussed and has been prepared in accordance with the generally accepted
standard of care for the profession. No warranties express or implied, are made. The
conclusions and recommendations contained in this report should not be considered valid
in the event that any changes in the nature, design or location of the project as outlined in
this report are planned, unless those changes are reviewed and the conclusions of this
report modified and verified in writing by the geotechnical engineer.
LOG OF BORING B-1
1/1 CME 55
4" CFA
Manual
BMc
Estimated Swell % Passing
SOIL DESCRIPTION Depth "N" MC DD qu
% Swell @ Pressure # 200 Sieve
(ft) (%) (pcf) (psf) 500 psf (psf) LL PI (%)
0 - 4" VEGETATION & TOPSOIL -
1
-
2
-
CL LEAN CLAY with varying 3 CS 13 8.0 112.1 9000+ None <500 - - -
amounts of SILT and SAND -
light brown to reddish brown 4
stiff to very stiff -
5 CS 21 16.6 110.7 9000+ 0.5% 1250 33 19 78.6%
-
6
-
7
-
8
-
9
-
SP-GP SAND and GRAVEL 10 CS 50/10 2.9 97.3 N/A - - - - -
reddish brown -
dense to very dense 11
-
Possible Cobbles 12-15' 12
-
13
-
14
-
15 CS 50/2 - - - - - - - -
BOTTOM OF BORING @ 15.0' -
16
-
17
-
18
-
19
-
20
-
21
-
22
-
23
-
24
-
25
PROPOSED OFFICE BUILDING
LOG OF BORING B-2
1/1 CME 55
4" CFA
Manual
BMc
Estimated Swell % Passing
SOIL DESCRIPTION Depth "N" MC DD qu
% Swell @ Pressure # 200 Sieve
(ft) (%) (pcf) (psf) 500 psf (psf) LL PI (%)
-
1
-
2
CL LEAN CLAY with varying -
amounts of SILT and SAND 3
light brown to reddish brown -
very stiff 4
-
5 CS 24 13.7 114.1 9000+ 2.4% 4000 - - -
-
6
-
7
-
8
-
9
-
10 CS 30 10.7 122.3 9000+ 2.9% 3500 - - -
-
11
-
12
SP-GP SAND and GRAVEL -
reddish brown 13
very dense -
14
-
15 CS 50/7 3.6 114.1 N/A - - - - -
BOTTOM OF BORING @ 15.0' -
16
-
17
-
18
-
19
-
20
-
21
-
22
-
23
-
24
-
25
PROPOSED OFFICE BUILDING
Liquid Limit -
Plasticity Index -
% Passing #200 -
Dry Density 112.1 pcf
Sample Description: Reddish Brown Silty/Sandy Lean Clay (CL)
Sample ID: B-1 @ 2'
PROPOSED OFFICE BUILDING
215 MATTHEWS STREET, FORT COLLINS, COLORADO
Project # 15-1056
April 2015
SWELL/CONSOLIDATION TEST SUMMARY
None
<500 psf
Initial Moisture
Final Moisture
% Swell @ 500 psf
Swell Pressure
8.0%
16.9%
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
10 100 1000 10000 100000
---------
Applied Load (psf)
Liquid Limit 33
Plasticity Index 19
% Passing #200 78.6%
Dry Density 110.7 pcf
Final Moisture 18.8%
% Swell @ 500 psf 0.5%
Swell Pressure 1,250 psf
Sample ID: B-1 @ 4'
Sample Description: Light Brown to Brown Sandy Lean Clay (CL)
Initial Moisture 16.6%
PROPOSED OFFICE BUILDING
215 MATTHEWS STREET, FORT COLLINS, COLORADO
Project # 15-1056
April 2015
SWELL/CONSOLIDATION TEST SUMMARY
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
10 100 1000 10000 100000
---------
Applied Load (psf)
Liquid Limit -
Plasticity Index -
% Passing #200 -
Dry Density 114.1 pcf
Final Moisture 19.5%
% Swell @ 500 psf 2.4%
Swell Pressure 4,000 psf
Sample ID: B-2 @ 4'
Sample Description: Reddish Brown Sandy Lean Clay (CL)
Initial Moisture 13.7%
PROPOSED OFFICE BUILDING
215 MATTHEWS STREET, FORT COLLINS, COLORADO
Project # 15-1056
April 2015
SWELL/CONSOLIDATION TEST SUMMARY
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
10 100 1000 10000 100000
---------
Applied Load (psf)
Liquid Limit -
Plasticity Index -
% Passing #200 -
Dry Density 122.3 pcf
Final Moisture 15.8%
% Swell @ 500 psf 2.9%
Swell Pressure 3500 psf
Sample ID: B-2 @ 9'
Sample Description: Reddish Brown Sandy Lean Clay (CL)
Initial Moisture 10.7%
PROPOSED OFFICE BUILDING
215 MATTHEWS STREET, FORT COLLINS, COLORADO
Project # 15-1056
April 2015
SWELL/CONSOLIDATION TEST SUMMARY
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
10 100 1000 10000 100000
---------
Applied Load (psf)
Resistivity (ohms-cm) Corrosion Condition
< 2,300 very aggressive
2,300- 5,000 moderately aggressive
5,000- 10,000 slightly aggressive
> 10,000 non- aggressive
Aggressivity Aggressivity
pH Range Acid/Base to Lead to Iron and Steel
< 4 extremely acidic very aggressive very aggressive
4.0- 4.5 very acidic very aggressive very aggressive
4.5- 5.0 acidic slightly aggressive very aggressive
5.0-6.0 slightly acidic slightly aggressive very aggressive
6.0- 6.5 slightly acidic slightly aggressive aggressive
6.5- 7.5 neutral non- aggressive non- aggressive
7.5- 8.5 slightly alkaline non- aggressive non- aggressive
> 8.5 very alkaline very aggressive doubtful
Exposure In water (ppm)
Negligible < 150
Moderate 150 to 1500
Severe 1500 to 10000
Very Severe > 10000
ACI 318-11
" Corrosion of Metals in the Underground and Underground Telephone Plant"
by George Schick, Bell Telephone Laboratories
In soil, percent by weight
< 0.1
(Level of Sulfate Attack of Concrete Exposed to Soils)
CORROSIVE SOIL CHARACTERISTICS
(Degree of Aggression for Corrosion of Buried Ferrous Metals Exposed to Soil)
(Degree of Aggression for Corrosion of Buried Lead, Iron and Steel Exposed to Soil)
0.1 to 0.2
0.2 to 2.0
> 2.0
WATER SOLUBLE SULFATES
Concentration of soluble sulfates expressed as SO4
SOIL RESISTIVITY
SOIL pH
UNIFIED SOIL CLASSIFICATION SYSTEM
Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification
Group
Symbol
Group NameB
Clean Gravels Cu ! 4 and 1 " Cc " 3E GW Well graded gravelF
Less than 5% finesC Cu
< 4 and/or 1 > Cc > 3E GP Poorly graded gravelF
Fines classify as ML or MH GM Silty gravelF,G, H
Coarse Grained Soils
More than 50% retained
on No. 200 sieve
Gravels
More than 50% of coarse
fraction retained on
No. 4 sieve Gravels with Fines More
than 12% finesC Fines classify as CL or CH GC Clayey gravelF,G,H
Clean Sands Cu ! 6 and 1 " Cc " 3E SW Well graded sandI
Less than 5% finesD Cu
< 6 and/or 1 > Cc > 3E SP Poorly graded sandI
Fines classify as ML or MH SM Silty sandG,H,I
Sands
50% or more of coarse
fraction passes
No. 4 sieve Sands with Fines
More than 12% finesD Fines classify as CL or CH SC Clayey sandG,H,I
Silts and Clays PI > 7 and plots on or above “A” lineJ CL Lean clayK,L,M
Liquid limit less than 50
Inorganic
PI < 4 or plots below “A” lineJ ML SiltK,L,M
Liquid limit - oven
dried
Organic clayK,L,M,N
Fine-Grained Soils
50% or more passes the
No. 200 sieve
Organic
Liquid limit - not
dried
< 0.75 OL
Organic siltK,L,M,O
Inorganic PI plots on or above “A” line CH Fat clayK,L,M
Silts and Clays
Liquid limit 50 or more
PI plots below “A” line MH Elastic siltK,L,M
Organic Liquid limit - oven dried Organic clayK,L,M,P
Liquid limit - not dried
< 0.75 OH
Organic siltK,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-in. (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 =
GENERAL NOTES
DRILLING & SAMPLING SYMBOLS:
SS: Split Spoon - 1⅜" I.D., 2" O.D., unless otherwise noted HS: Hollow Stem Auger
ST: Thin-Walled Tube – 2.5" O.D., unless otherwise noted PA: Power Auger
RS: Ring Sampler - 2.42" I.D., 3" O.D., unless otherwise noted HA: Hand Auger
CS: California Barrel - 1.92" I.D., 2.5" O.D., unless otherwise noted RB: Rock Bit
BS: Bulk Sample or Auger Sample WB: Wash Boring or Mud Rotary
The number of blows required to advance a standard 2-inch O.D. split-spoon sampler (SS) the last 12 inches of the total 18-inch
penetration with a 140-pound hammer falling 30 inches is considered the “Standard Penetration” or “N-value”. For 2.5” O.D.
California Barrel samplers (CB) the penetration value is reported as the number of blows required to advance the sampler 12
inches using a 140-pound hammer falling 30 inches, reported as “blows per inch,” and is not considered equivalent to the
“Standard Penetration” or “N-value”.
WATER LEVEL MEASUREMENT SYMBOLS:
WL: Water Level WS: While Sampling
WCI: Wet Cave in WD: While Drilling
DCI: Dry Cave in BCR: Before Casing Removal
AB: After Boring ACR: After Casing Removal
Water levels indicated on the boring logs are the levels measured in the borings at the times indicated. Groundwater levels at other
times and other locations across the site could vary. In pervious soils, the indicated levels may reflect the location of groundwater.
In low permeability soils, the accurate determination of groundwater levels may not be possible with only short-term observations.
DESCRIPTIVE SOIL CLASSIFICATION: Soil classification is based on the Unified Classification System. Coarse Grained Soils
have more than 50% of their dry weight retained on a #200 sieve; their principal descriptors are: boulders, cobbles, gravel or sand.
Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are principally described as clays if they
are plastic, and silts if they are slightly plastic or non-plastic. Major constituents may be added as modifiers and minor constituents
may be added according to the relative proportions based on grain size. In addition to gradation, coarse-grained soils are defined
on the basis of their in-place relative density and fine-grained soils on the basis of their consistency.
FINE-GRAINED SOILS COARSE-GRAINED SOILS BEDROCK
(CB)
Blows/Ft.
(SS)
Blows/Ft.
Consistency
(CB)
Blows/Ft.
(SS)
Blows/Ft.
Relative
Density
(CB)
Blows/Ft.
(SS)
Blows/Ft.
Consistency
< 3 0-2 Very Soft 0-5 < 3 Very Loose < 24 < 20 Weathered
3-5 3-4 Soft 6-14 4-9 Loose 24-35 20-29 Firm
6-10 5-8 Medium Stiff 15-46 10-29 Medium Dense 36-60 30-49 Medium Hard
11-18 9-15 Stiff 47-79 30-50 Dense 61-96 50-79 Hard
19-36 16-30 Very Stiff > 79 > 50 Very Dense > 96 > 79 Very Hard
> 36 > 30 Hard
RELATIVE PROPORTIONS OF SAND AND
GRAVEL
GRAIN SIZE TERMINOLOGY
Descriptive Terms of
Other Constituents
Percent of
Dry Weight
Major Component
of Sample
Particle Size
Trace < 15 Boulders Over 12 in. (300mm)
With 15 – 29 Cobbles 12 in. to 3 in. (300mm to 75 mm)
Modifier > 30 Gravel 3 in. to #4 sieve (75mm to 4.75 mm)
Sand
Silt or Clay
#4 to #200 sieve (4.75mm to 0.075mm)
Passing #200 Sieve (0.075mm)
RELATIVE PROPORTIONS OF FINES PLASTICITY DESCRIPTION
Descriptive Terms of
Other Constituents
Percent of
Dry Weight
Term Plasticity Index
Trace
With
Modifiers
< 5
5 – 12
> 12
Non-plastic
Low
Medium
High
0
1-10
11-30
30+
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.
HIf 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.
215 MATTHEWS STREET, FORT COLLINS, COLORADO
Project # 15-1056
April 2015
Sheet Drilling Rig: Water Depth Information
Start Date 3/23/2015 Auger Type: During Drilling None
Finish Date 3/23/2015 Hammer Type: After Drilling None
Surface Elev. - Field Personnel: 24 Hours After Drilling Dry Cave @ 13'
USCS
Sampler
Atterberg Limits
Atterberg Limits
Dry Cave @ 12'
During Drilling
After Drilling
Sheet
Start Date
Finish Date
24 Hours After Drilling
Water Depth Information
3/23/2015 13.5
215 MATTHEWS STREET, FORT COLLINS, COLORADO
Project # 15-1056
April 2015
Sampler
USCS
Surface Elev.
13.5
Auger Type:
Drilling Rig:
Hammer Type:
Field Personnel:
3/23/2015
-