HomeMy WebLinkAboutFOSSIL CREEK OFFICE PARK EAST PUD PRELIMINARY AND FINAL - 52 91B - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTGEOTECHNICAL ENGINEERING REPORT
CAMERON PARK OFFICE BUILDINGS
SOUTH COLLEGE AVENUE
FORT COLLINS, COLORADO
TERRACON PROJECT NO. 20955185
November 13, 1995
Irerracon
Geotechnical Engineering Exploration Terracon
Lagunitas Company
Terracon Project No. 20955185
Groundwater Conditions: Groundwater was encountered in Boring 6 at a depth of 9 feet
and the remaining borings were dry at the time of field exploration. When checked four
days after drilling, groundwater was measured in Borings 1 through 9, 11 and 12 at
approximate depths of 5'/2 to 14'/z feet. Borings 10 and 13 through 17 remained dry four
days after drilling. These observations represent only current groundwater conditions, and
may not be indicative of other times, or at other locations. Groundwater levels can be
expected to fluctuate with varying seasonal and weather conditions.
Based upon review of U.S. Geological Survey Maps ('Hillier, et al, 1983), regional
groundwater beneath the project area predominates in colluvial, landslide or windblown
materials, or in fractured weathered consolidated sedimentary bedrock located at a depth
near ground surface. Seasonal variations in groundwater conditions are expected since the
aquifer materials may not be perennially saturated. Groundwater is generally encountered
at depths ranging from 5 to 20 feet below ground surface; depth to seasonal groundwater
7 is generally 10 feet or less. At the lower elevations of the site, regional groundwater is
expected to be encountered in unconsolidated alluvial deposits, at depths ranging from 5
to 10 feet below the existing ground surface.
Zones of perched and/or trapped groundwater may also occur at times in the subsurface
soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the
bedrock materials. The location and amount of perched water is dependent upon several
factors, including hydrologic conditions, type of site development, irrigation demands on or
adjacent to the site, fluctuations in water features, and seasonal and weather conditions.
-y —.Fluctuations.__in groundwater levels can best be determined by implementation of a
Jgroundwater monitoring plan. Such a plan would include installation of groundwater
monitoring wells, and periodic measurement of groundwater levels over a sufficient period
of time.
The possibility of groundwater fluctuations should be considered when developing design
and construction plans for the project, by implementing the recommendations presented
herein.
2Hillier, Donald E.; Schneider, Paul A., Jr.; and Hutchinson, E. Carter, 1983, Depth to Water Table (1979) in the
Boulder -Fort Collins -Greeley Area, Front Range Urban Corridor Colorado, United States Geological Survey, Map 1-855-I.
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Geotechnical Engineering Exploration Terracon
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Terracon Project No. 20955185
CONCLUSIONS AND RECOMMENDATIONS
Geotechnical Considerations: The site appears suitable for the proposed construction.
Potentially expansive soils, groundwater and bedrock will require particular attention in the
design and construction.
The following foundation systems were evaluated for use on the site:
• spread footings and/or grade beams bearing on undisturbed soils and/or
bedrock; and,
• spread footings and/or grade beams bearing on engineered fill extended to the
undisturbed soil and/or bedrock.
Slab -on -grade construction is considered acceptable for use, provided that design and
construction recommendations are followed.
Foundation Systems: Due to the presence of non- to low -swelling soils on the site, spread
footing foundations bearing upon undisturbed subsoils and/or engineered fill are
recommended for support for the proposed structures. The footings may be designed for
a maximum bearing pressure of 1,500 psf. Footings for structures bearing entirely on the
bedrock stratum may be designed for a maximum allowable bearing capacity of 3,000 psf.
In addition, the footings should be sized to maintain a minimum dead -load pressure of 500
psf. The design bearing pressure applies to dead loads plus 1 /2 of design live load
conditions. The design bearing pressure may be increased by one-third when considering
-total loads that include wind or seismic conditions.
Existing fill on the site should not be used for support of foundations without removal and
recompaction. All debris and organic material should be removed from the fill'prior to its
reuse. Any additional fill should be placed prior to foundation construction to allow for
some consolidation of the subsoils from the added weight of the new fill.
Exterior footings should be placed a minimum of 30 inches below finished grade for frost
protection. Finished grade is the lowest adjacent grade for perimeter footings and floor level
for interior footings.
Footings should be proportioned to minimize differential foundation movement.
Proportioning on the basis of equal total settlement is recommended; however,
proportioning to relative constant dead -load pressure will also reduce differential settlement
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Geotechnical Engineering Exploration Terracon
Lagunitas Company
Terracon Project No. 20955185
9 between adjacent footings. Total settlement resulting from the assumed structural loads
Jis estimated to be on the order of 3/4 inch. Proper drainage should be provided in the final
design and during construction to reduce the settlement potential.
For foundations adjacent to slopes, a minimum horizontal setback of five (5) feet should be
maintained between the foundation base and slope face. In addition, the setback should
be such that an imaginary line extending downward at 45 degrees from the nearest
foundation edge does not intersect the slope.
Foundations and masonry walls should be reinforced as necessary to reduce the potential
for distress caused by differential foundation movement. The use of joints at openings or
other discontinuities in masonry walls is recommended.
Foundation excavations should be observed by the geotechnical engineer. If the soil
conditions encountered differ from those presented in this report, supplemental
recommendations will be required.
,] Basement Construction: Groundwater was encountered on the majority of the site at
depths of 5'/z to 14'/2 feet below existing grade. Full -depth basement construction is
J considered feasible on the site provided complete dewatering systems are placed around
all basement areas and lower areas of structures placed in or within 3 feet of the bedrock
and/or groundwater.
Perched groundwater occurs at times since the bedrock surface is relatively impermeable
and may -tend to trap water. Completion of site development, including installation of
landscaping and irrigation systems, will likely lead to increased perched groundwater
development.
To reduce the potential for groundwater to enter the basement of the structure, installation
of a dewatering system is recommended. The dewatering system should, at a minimum,
include an underslab gravel drainage layer sloped to a perimeter drainage system.
The drainage system should be constructed around the exterior perimeter of the basement
foundation and should consist of a properly sized perforated pipe, embedded in free -draining
gravel, placed in a trench at least 12 inches in width. The gravel should extend a minimum
of 3-inches beneath the bottom of the pipe and at least 1 foot above the bottom of the
foundation wall. The gravel should be covered with drainage fabric prior to placement of
foundation backfill.
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Terracon
The drainage system should slope at least'/a inch per foot and should daylight away from
the building or empty into a suitable outlet, such as a sump and pump system or storm
drain. Where groundwater is encountered at relatively shallow depths, consideration shall
be given to use of garden -level or slab -on -grade construction. Where basements are
excavated below groundwater, temporary dewatering will be required. Where a sump and
pump is used to discharge groundwater below basement levels, alternating pumps and a
backup generator are recommended in case of mechanical and/or electrical failure.
The underslab drainage layer should consist of a minimum 8-inch thickness of free -draining
gravel meeting the specifications of ASTM C33, Size No. 57 or 67.
Seismic Considerations: The project site is located in Seismic Risk Zone I of the Seismic
Zone Map of the United States as indicated by the 1994 Uniform Building Code. Based
upon the nature of the subsurface materials, a seismic site coefficient, "s" of 1.0 should
be used for the design of structures for the proposed project (1994 Uniform Building Code,
Table No. 16-J).
Floor Slab Design and Construction: Non -expansive or low -swelling natural soils or
engineered fill will support the floor slab. Some differential movement of a slab -on -grade
floor system is possible should the subgrade soils increase in moisture content. Such
movements are considered within general tolerance for normal slab -on -grade construction.
To reduce any potential slab movements, the subgrade soils should be prepared as outlined
in the "Earthwork" section of this report.
--Additional_floor.slab design and construction recommendations are as follows:
• Positive separations and/or isolation joints should be provided between slabs
and all foundations, columns or utility lines to allow independent movement.
• Contraction joints should be provided in slabs to control the location and
extent of cracking. The American Concrete Institute (ACI) recommends the
control joint spacing in feet for nonstructural slabs should be 2 to 3 times the
slab thickness in inches in both directions. Maximum joint spacing of 15 to
20 feet in each direction is recommended. Sawed or tooled joints should
have a minimum depth of 25% of slab thickness plus '/. inch.
• Interior trench backfill placed beneath slabs should be compacted in
accordance with recommended specifications outlined below.
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• in areas subjected to normal loading, a minimum 4-inch layer of clean -graded
gravel should be placed beneath interior slabs. For heavy loading,
reevaluation of slab and/or base course thickness may be required.
• A minimum 8-inch layer of free -draining gravel should be placed beneath
basement floor slabs in conjunction with the underslab drainage system.
• If moisture sensitive floor coverings are used on interior slabs, consideration
should be given to the use of barriers to minimize potential vapor rise through
the slab.
• Floor slabs should not be constructed on frozen subgrade.
• Other design and construction considerations, as outlined in the ACI Design
Manual, Section 302.113 are recommended.
Pavement Design and Construction: The required total thickness for the pavement structure
is dependent primarily upon the foundation soil or subgrade and upon traffic conditions.
Based on the soil conditions encountered at the site, the type and volume of traffic and
using an average group index of 5 as the criterion for pavement design, the following
minimum pavement thicknesses are recommended:
Each alternative should be investigated with respect to current material availability and
economic conditions. Rigid concrete pavement, a minimum of 6 inches in thickness, is
recommended at the location of dumpsters where trash trucks will park and load.
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Geotechnical Engineering Exploration Terracon
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The pavement sections presented herein are based on design parameters selected by
Terracon based on experience with similar projects and soils conditions. Design parameters
such as design life, terminal serviceability index, modulus of rupture of .concrete and
inherent reliability may.vary with specific project. Variation of these parameters may
change the thickness of the pavement sections presented. Terracon is prepared to discuss
the details of these parameters and their effects on pavement design and reevaluate
pavement design as appropriate.
Aggregate base course (if used on the site) should consist of a blend of sand and gravel
which meets strict specifications for quality and gradation. Use of materials meeting
Colorado Department of Transportation (CDOT) Class 5 or 6 specifications is recommended
for base course.
Aggregate base course and select subbase should -be placed in lifts Inot exceeding six inches
and should be compacted to a minimum of 95% Standard Proctor Density (ASTM D698).
Asphalt concrete and/or plant -mixed bituminous base course should be composed of a
mixture of aggregate, filler and additives, if required, and approved bituminous material.
The bituminous base and/or asphalt concrete should conform to approved mix designs
stating the Marshall or Hveem properties, optimum asphalt content, job mix formula and
recommended mixing and placing temperatures. Aggregate used in plant -mixed bituminous
base course and/or asphalt concrete should meet particular gradations. Material meeting
Colorado Department of Transportation Grading C or CX specification is recommended for
asphalt concrete. Aggregate meeting Colorado Department of Transportation Grading G or
- C specifications is recommended for plant -mixed bituminous base course. Mix designs
should be submitted prior to construction to verify their adequacy. Asphalt material should
be placed in maximum 3-inch lifts and should be compacted to a minimum of 95% Marshall
or Hveem density (ASTM D1559) (ASTM D1560).
Where rigid pavements are used, the concrete should be obtained from an approved mix
design with the following minimum properties:
• Modulus of Rupture @ 28 days 650 psi minimum
• Strength Requirements ASTM C94
• Minimum Cement Content ..................... 6.5 sacks/cu. yd.
0 Cement Type.............Type I Portland
• Entrained Air Content ................... 6 to 8%
• Concrete Aggregate ............ ASTM C33 and CDOT Section 703
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Geotechnical Engineering Exploration Terracon
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• Aggregate Size ............................. 1 inch maximum
• Maximum Water Content ................... 0.49 lb/lb of cement
• Maximum Allowable Slump .......................... 4 inches
Concrete should be deposited by truck mixers or agitators and placed a maximum of 90
minutes from the time the water is added to the mix. Other specifications outlined by the
Colorado Department of Transportation should be followed.
Longitudinal and transverse joints should be provided as needed in concrete pavements for
expansion/contraction and isolation. The location and extent of joints.should be based upon
the final pavement geometry and should be placed (in feet) at roughly twice the slab
thickness (in inches) on center in either direction. Sawed joints should be cut within 24-
hours of concrete placement, and should be a minimum of 25% of slab thickness plus 1 /4
inch. All joints should be sealed to prevent entry of foreign material and dowelled where
necessary for load transfer. Where dowels cannot be used at joints accessible to wheel
loads, pavement thickness should be increased by 25 percent at the joints and tapered to
regular thickness in 5 feet.
Future performance of pavements constructed on the clay soils at this site will be
dependent upon several factors, including:
• maintaining stable moisture content of the subgrade soils and
• providing for a planned program of preventative .maintenance.
-- Since the clay soils on the site have shrink/swell characteristics, pavements could crack in
the future primarily because of expansion of the soils when subjected to an increase in
moisture content to the subgrade. The cracking, while not desirable, does not necessarily
-1 constitute structural failure of the pavement.
The performance of all pavements can be enhanced by minimizing excess moisture which
can reach the subgrade soils. The following recommendations should be considered at
minimum:
0 Site grading at a minimum 2% grade away from the pavements;
• Compaction of any utility trenches for landscaped areas to the same criteria
as the pavement subgrade;
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Geotechnical Engineering Exploration
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• Sealing all landscaped areas in or adjacent to pavements to minimize or
prevent moisture migration to subgrade soils;
• Placing compacted backfill against the exterior side of curb and gutter; and,
• Placing curb, gutter and/or sidewalk directly on subgrade soils without the
use of base course materials.
Preventative maintenance should be planned and provided for an on -going pavement
management program in order to enhance future pavement performance. Preventative
maintenance activities are intended to slow the rate of pavement deterioration and to
preservethe pavement, investment.
Preventative maintenance consists of both localized maintenance (e.g. crack sealing and
patching) and global maintenance (e.g. surface sealing). Preventative maintenance is
usually the first priority when implementing a planned pavement maintenance program and
provides the highest return on investment for pavements.
Recommended preventative maintenance policies for asphalt and jointed concrete
pavements, based upon type and severity of distress, are provided in Appendix D. Prior to
implementing any maintenance, additional engineering observation is recommended to
determine the type and extent of preventative maintenance.
Earthwork:
• Site Clearing and Subgrade Preparation:
i
1. Strip and remove existing vegetation, debris, and other deleterious materials
from proposed building and pavement areas. All exposed surfaces should be
free of mounds and depressions which could prevent uniform compaction.
2. If unexpected fills or underground facilities are encountered during site
clearing, such features should be removed and the excavation thoroughly
cleaned prior to backfill placement and/or construction. All excavations
should be observed by the geotechnical engineer prior to backfill placement.
3. Stripped materials consisting of vegetation and organic materials should be
wasted from the site or used to revegetate exposed slopes after completion
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Geotechnical Engineering Exploration Terracon
Lagunitas Company
Terracon Project No. 20955185
of grading operations. If it is necessary to dispose of organic materials on -
site, they should be placed in non-structural areas and in fill sections not
exceeding 5 feet in height.
4. Sloping areas steeper than 3:1 (horizontal:vertica1) should be benched to
reduce the potential for slippage between existing slopes and fills. Benches
should be level and wide enough to accommodate compaction and earth
moving equipment.
5. The site should be initially graded to create a relatively level surface to
receive fill, and to provide for a relatively uniform thickness of fill beneath
proposed building structures.
6. All exposed areas which will receive fill, floor slabs and/or pavement, once
properly cleared and benched where necessary, should be scarified to a
minimum depth of 8 inches, conditioned to near optimum moisture content,
and compacted.
0 Excavation:
1. It is anticipated that excavations in the upper soils for the proposed
construction can be accomplished with conventional earthmoving equipment.
2. Excavation penetrating the bedrock may require the use of specialized heavy-
duty equipment, together with drilling and blasting to facilitate rock break-up
and removal. If blasting is used to excavate footings; it should be carefully
done as not to disturb the foundation bedrock. All loose rock should be
removed from below foundations prior to placement of concrete.
3. Depending -upon depth of excavation and seasonal conditions, groundwater
may be encountered in excavations on the site. Groundwater seepage should
be anticipated for excavations approaching the level of bedrock. Pumping
from sumps may be utilized to control water within excavations. Well points
may be required for significant groundwater flow or where 'excavations
penetrate groundwater to a significant depth.
4. On -site clay soils in proposed pavement areas may pump or become unstable
or unworkable at high water contents. Workability may be improved by
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Geotechnical Engineering Exploration
Lagunitas Company
Terracon Project No. 20955185
Terracon
scarifying and drying. Overexcavation of wet zones and replacement with
granular materials may be necessary. Lightweight excavation equipment may
be required to reduce subgrade pumping.
Use of lime, fly ash, kiln dust, cement or geotextiles could also be considered
as a stabilization technique. Laboratory evaluation is recommended to
determine the effect of chemical stabilization on subgrade soils prior to
construction.
Proof -rolling of the subgrade may be required to determine stability prior to
paving.
• Fill Materials:
1. Clean on -site soils or approved imported materials may be used as fill material
for the following:
• general site grading
• foundation areas
• interior floor slab areas
• exterior slab areas
• pavement areas
• foundation backfill
2. Select granular materials should be used as backfill behind retaining walls.
3. Frozen soils should not be used as fill or backfill.
4. Imported soils (if required) should conform to the following or be'approved- `-
by the Project Geotechnical Engineer:
Percent finer by weight
Gradation (ASTM C136)
6.. ......................................... 100
3.. ....................................... 70-100
No. 4 Sieve .................................. 50-80
No. 200 Sieve .............................. 50 (max)
• Liquid Limit 35 (max)
• Plasticity Index ......................... 15 (max)
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GEOTECHNICAL ENGINEERING REPORT
CAMERON PARK OFFICE BUILDINGS
SOUTH COLLEGE AVENUE
FORT COLLINS, COLORADO
TERRACON PROJECT NO. 20955185
November 13, 1995
Prepared for.
LAGUNITAS COMPANY
3303 SOUTH COLLEGE AVENUE, SUITE 200
FORT COLLINS, COLORADO 80525
ATTN: MR. JOHN PROUTY
lferracon
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Geotechnical Engineering Exploration Terracon
Lagunitas Company
`j Terracon Project No. 20955185
5. Aggregate base should conform to Colorado Department of Transportation
Class 5 or 6 specifications.
• Placement and Compaction:
1. Place and compact fill in horizontal lifts, using equipment and procedures that
will produce recommended moisture contents and densities throughout the
lift.
2. No fill should be placed over frozen ground.
3. Materials should be compacted to the following:
Minimum Percent
JMaterial (ASTM D698)
Subgrade soils beneath fill areas ..................... 95
JOn -site soils or approved imported fill:
Beneath foundations ......................... 98
Beneath slabs 95
Beneath pavements 95
Utilities....................................... 95
Aggregate base (beneath slabs) ...................... 95
Miscellaneous"backfill ............................. 90
4. If a well defined maximum density curve cannot be generated by impact
compaction in the laboratory for any fill type, engineered fill should be
compacted to a minimum of 80 percent relative density as determined by
ASTM D4253 D4254.
5. Granular soils should be compacted within a moisture content range of 3
percent below to 3 percent above optimum unless modified by the project
geotechnical engineer.
6. Clay soils placed around or beneath foundations should be compacted within
a moisture content range of optimum to 2 percent above optimum. Clay soils
placed beneath pavement should be compacted within a moisture content
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Geotechnical Engineering Exploration
Lagunitas Company
Terracon Project No. 20955185
range of 2 percent below to 2 percent above optimum.
• Compliance: Performance of slabs -on -grade, foundations and pavement elements
supported on compacted fills or prepared subgrade depend upon compliance with
"Earthwork" recommendations. To assess compliance, observation and testing
should be performed under the direction of the geotechnical engineer.
• Excavation and Trench Construction: Excavations into the on -site soils will
encounter a variety of conditions. Excavations into the clays and bedrock can be
expected to stand on relatively steep temporary slopes during construction.
However, caving soils and/or groundwater may also be encountered. The individual
contractor(s) should be made responsible for designing and constructing stable,
temporary excavations as required to maintain stability of both the excavation sides
and bottom. All excavations should be sloped or shored in the interest of. safety
following local and federal regulations, including current OSHA excavation and
trench safety standards.
Drainage:
• Surface Drainage:
1. Positive drainage should be provided during construction and maintained
throughout the life of the proposed office buildings. Infiltration of water into
utility or foundation excavations must be prevented during construction.
Planters and other surface features which could retain water in areas adjacent
to the building or pavements should be sealed or eliminated.
2. In areas where sidewalks or paving do not immediately adjoin the structure,
we recommend that protective slopes be provided with a minimum grade of
approximately 10 percent for at least 10 feet from perimeter walls. Backfill
against footings, exterior walls and in utility and sprinkler line trenches should
be well compacted and free of all construction debris to reduce the possibility
of moisture infiltration.
3. Downspouts, roof drains or scuppers should discharge into splash blocks or
extensions when the ground surface beneath such features is not protected
by exterior slabs or paving.
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Geotechnical Engineering Exploration Terracon
Lagunitas Company
Terracon Project No. 20955185
4. Sprinkler systems should not be installed within 5 feet of foundation walls.
Landscaped irrigation adjacent to the foundation system should be minimized
or eliminated.
• Subsurface Drainage: Free -draining, granular soils containing less than five percent
fines (by weight) passing a No. 200 sieve should be placed adjacent to walls which
retain earth. A drainage system consisting of either weep holes or perforated drain
lines (placed near the base of the wall) should be used to intercept and discharge
water which would tend to saturate the backfill. Where used, drain lines should be
embedded in a uniformly graded filter material and provided with adequate clean -outs
for periodic maintenance. An impervious soil should be used in the upper layer of
backfill to reduce the potential for water infiltration.
Additional Design and Construction Considerations:
• Exterior Slab Design and Construction: Exterior slabs -on -grade, exterior architectural
features, and utilities founded on, or in backfill may experience some movement due
to the volume change of the backfill. Potential movement could be reduced by:
• minimizing moisture increases in the backfill
• controlling moisture -density during placement of backfill
• using designs which allow vertical movement between the exterior
features and adjoining structural elements
• placing effective control joints on relatively close centers
• allowing -vertical movements in utility connections .
• Underground Utility Systems: All piping should be adequately bedded for proper load
distribution. It is suggested that clean, graded gravel compacted to 75 percent of
Relative Density ASTM D4253 be used as bedding. Where utilities are excavated
below groundwater, temporary dewatering will be required during excavation, pipe
placement and backfilling operations for proper construction. Utility trenches should
be excavated on safe and stable slopes in accordance with OSHA regulations as
discussed above. Backfill should consist of the on -site soils or existing bedrock. If
bedrock is used; all plus 6-inch material should be removed from it prior to its use.
The pipe backfill should be compacted to a minimum of 95 percent of Standard
Proctor Density ASTM D698.
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Geotechnical Engineering Exploration Terracon
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• Corrosion Protection: Results of soluble sulfate testing indicate that ASTM Type 1-II
Portland cement is suitable for all concrete on or below grade. Foundation concrete
should be designed in accordance with the provisions of the ACI Design Manual,
JSection 318, Chapter 4.
IGENERAL COMMENTS
It is recommended that the Geotechnical Engineer be retained to provide a general review
of final design plans and specifications in order to confirm that grading and foundation
recommendations have been interpreted and implemented. In the event that any changes
of the proposed project are planned, the conclusions and recommendations contained in this
report should be reviewed and the report modified or supplemented as necessary.
The Geotechnical Engineer should also be retained to provide services during excavation,
grading, foundation and construction phases of the work. Observation of footing
excavations should be performed prior to placement of reinforcing and concrete to confirm
that satisfactory bearing materials are present and is considered a necessary part of
continuing geotechnical engineering services for the project. Construction testing, including
field and laboratory evaluation of fill, backf ill, pavement materials, concrete and steel should
be performed to determine whether applicable project requirements have been met. It
J would be logical for Terracon Consultants Western, Inc. to provide these additional services
for continuing from design through construction and to determine the consistency of field
conditions with those data used in our analyses.
The analyses and recommendations in this report are based in part upon data obtained from
the field exploration. The nature and extent of variations beyond the location of test
borings may not become evident until construction. If variations then appear evident, it
may be necessary to re-evaluate the recommendations of this report.
Our professional services were performed using that degree of care and skill ordinarily
exercised, under similar circumstances, by reputable geotechnical engineers practicing in
this or similar localities. No warranty, express or implied, is made. We prepared the report
as an aid in design of the proposed project. This report is not a bidding document. Any
contractor reviewing this report must draw his own conclusions regarding site conditions
and specific construction techniques.to be used on this project.
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Geotechnical Engineering Exploration
Lagunitas Company
Terracon Project No. 20955185
Terracon
This report is for the exclusive purpose of providing geotechnical engineering and/or testing
information and recommendations. The scope of services for this project does not include,
either specifically or by implication, any environmental assessment of the site or
identification of contaminated or hazardous materials or conditions. If the owner is
concerned about the potential for such contamination, other studies should be undertaken.
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FIGGURE 1: SITE PLAN
S. COLLEGE AVE. & CAMRON. DR.
FORT COLLINS, COLORADO
ELI. PROJECT No. 20955185
T,13.M. &- FE QF
f LEev, = C04.o$'
CONSULTANTS WESTERN. INC.
EMPIRE DIVISION
Irerracon
CONSULTANTS WESTERN, INC.
P.O. Box 503 •301 N. Howes
Fort Collins, Colorado 80522
(970) 484-0359 Fax (970) 484-0454
Chester C. Smith, P.E.
Larry G. O'Dell, P.E. '
Neil R. Sherrod, C.P.G.
November 13, 1995
Lagunitas Company
3303 South College Avenue, Suite 200
Fort Collins, Colorado 80525
Attn: Mr. John Prouty
Re: Geotechnical Engineering Report, Cameron Park Office Buildings
South College Avenue, Fort Collins, Colorado
Terracon Project No. 20955185
Terracon Consultants Western, Inc., Empire Division has completed a geotechnical engineering .
exploration for the proposed office park to be located on South College Avenue, Fort Collins,
Colorado. This study was performed in general accordance with our proposal number D2095265
dated October 19, 1995.
The results of our engineering study, including the boring location diagram, laboratory test results,
test boring records, and the geotechnical recommendations needed to aid in the design and
construction of foundations and other earth connected phases of this project are attached. The
subsoils at the site consist of sands and clays underlain by sandstone bedrock. It is recommended
the proposed structures be supported by conventional -type spread footings and/or grade beam
foundation systems founded on the original, undisturbed soil and/or bedrock stratum. Excavation
of the firm bedrock may be difficult, and complete dewatering systems will be required for basement
construction. Further details are provided in this report.
We appreciate the opportunity to be of service to you on this phase of your project. If you have any
questions concerning this report, or if we may be of further service to you, please do not hesitate
to -contact us.
Sincerely, tf ®� ®ce're
TERRACON CONSULTANTS WESTERN, INC. o010- toei?EGN
Empire Division eV�o.•e�eQQ+ �• AT}°°•e�9�
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Prepared by: /. \��1�OfPAOFESSipy Reviewe ®"O�Qo�.ts
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GATE N*`B �4Eo e
2575 F9 •; o ee a �e4
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AIPG 4,
eil . Sh r f'•.••N AtAftfir* 0,
Senior Engineering Geologist •� •.,ham.,;. Q \�' Assistant Offictv s
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Copies to: Addressee (3) PTaress,
Offices of The Terracon Companies, Inc. Geotechnical, Environmental and Materials Engineers
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QUALITY ENGINEERING SINCE 1965
11
Geotechnical Engineering Exploration Terracon
Lagunitas Company
Terracon Project No. 20955185
TABLE OF CONTENTS
y Page No.
Letter of Transmittal ...............................................`
INTRODUCTION................................................ 1
PROPOSED CONSTRUCTION . 1
SITE EXPLORATION ............................................. 1
Field Exploration .......................................... 2
Laboratory Testing 2
SITE CONDITIONS .............................................. 3
SUBSURFACE CONDITIONS .......................................
3
Geology ..................
3
Soil and Bedrock Conditions ..............................
4
Field and Laboratory Test Results ...............................
4
Groundwater Conditions .....................................
5
CONCLUSIONS AND RECOMMENDATIONS ............................
6
Geotechnical Considerations ........ • • • • • • • • • • • • • • •
6
Foundation Systems ............................. • • • • •
6
Basement Construction .......................................
7
Seismic Considerations
8
.......... : ...........................
Floor Slab Design and Construction
8
Pavement Design' and Construction .............................
9
---
-- Earthwork a ............. .. . ....^_.
12
x
.................... _
Site Clearing Subgrade Preparation .
12'
.and
Excavation.........................................
13
Fill Materials ........................................
14
Placement and Compaction
15
Compliance.........................................
16
Excavation and Trench Construction ..... ...........
16
Drainage :::::::
:
16
Surface Drainage ....................
16
Subsurface Drainage ...................................
17
Additional Design and Construction Considerations ..................
17
17.
Exterior Slab Design and Construction .....................
Underground Utility Systems .............................
17
Corrosion Protection ...................................
18
18
GENERAL COMMENTS ...........................................
J1
,
11,
Geotechnical Engineering Exploration Terracon
Lagunitas Company
Terracon Project No. 20955185
TABLE OF CONTENTS (Cont'd)
APPENDIX A
Figure
No.
SitePlan ................................ ...... .......
1
Logs of Borings .................................... Al thru Al
APPENDIX B
Consolidation Test .................................... 131 thru
B8
Summary of Laboratory Test Results ............................
B9
APPENDIX C: GENERAL NOTES
Drilling & Exploration .......................................
C1
Unified Soil Classification ....................................
C2
Bedrock Classification, Sedimentary Bedrock .......................
C3
Laboratory Testing, Significance and Purpose ......................
C4
Report Terminology ........................................
C5
APPENDIX D
Recommended Preventative Maintenance -Asphalt Concrete Pavements ....
D1
Recommended Preventative Maintenance -Jointed Concrete Pavements ....
D2
I
GEOTECHNICAL ENGINEERING REPORT Terracon
J CAMERON PARK OFFICE BUILDINGS
SOUTH COLLEGE AVENUE
FORT COLLINS, COLORADO
JTerracon Project No. 20955185
November 13, 1995
INTRODUCTION
This report contains the results of our geotechnical engineering exploration for the proposed
office buildings to be located in Cameron Park on South College Avenue, Fort Collins,
J Colorado. More particularly, the site is described as Lots 5 and 9 through 15, Cameron Park
2nd Filing located in the Southeast 1 /4 of Section 2, Township 6 North, Range 69 West of
the 6th Principal Meridian.
The purpose of these services is to provide information and geotechnical engineering
recommendations relative to:
• subsurface soil and bedrock conditions
• groundwater conditions
• foundation design and construction
• basement construction
• floor slab design and construction
• pavement design and construction
• earthwork
• drainage
i The conclusions -and recommendations contained in this report are based upon the results_
JJ of field and laboratory testing, engineering analyses, and experience with similar soil
conditions, structures and our understanding of the proposed project.
t
PROPOSED CONSTRUCTION
Based on information provided by Mr. John Prouty of Lagunitas Company, the proposed
structures will be one- and two-story office buildings with lofts. The buildings will have
walkout basement construction. Wall and column loads are reported to be 2 kips per linear
foot and 40 kips, respectively.
SITE EXPLORATION
The scope of the services performed for this project included site reconnaissance by a
geotechnical engineer, a subsurface exploration program, laboratory testing and engineering
analysis.
Geotechnical Engineering Exploration
Lagunitas Company-
JTerracon Project No. 20955185
Terracon
J Field Exploration: A total of 17 test borings were drilled on October 26, 1995 to depths of
10 to 15 feet at the locations shown on the Site Plan, Figure 1. Fourteen borings were
drilled within the footprints of the proposed buildings, and 3 borings were drilled in the area
i of proposed pavements. All borings were advanced with a truck -mounted drilling rig,
J utilizing 4-inch diameter solid stem auger.
JThe borings were located in the field by pacing from property lines and/or existing site
features. Elevations were taken at each boring location by measurements with an
J engineer's level from a temporary bench mark (TBM) shown on the Site Plan. The accuracy
of boring locations and elevations should only be assumed to the level implied by the
methods used.
JContinuous lithologic logs of each boring were recorded by the geotechnical engineer during
the drilling operations. At selected intervals, samples of the subsurface materials were
Jtaken by pushing thin -walled Shelby tubes, or by driving split -spoon samplers.
Representative bulk samples of subsurface materials were obtained from pavement borings.
Penetration resistance measurements were obtained by driving the split -spoon into the
subsurface materials with a 140-pound hammer falling 30 inches. The penetration
J resistance value is a useful index to the consistency, relative density or hardness of the
materials encountered.
Groundwater measurements were made in each boring at the time of site exploration, and
4 days after drilling.
Laboratory Testing: All samples retrieved during the field exploration were returned to the
laboratory for observation by the project geotechnical engineer, and were classified in
1 accordance with the Unified Soil Classification System described in Appendix C. Samples
J of bedrock were classified in accordance with the general notes for Bedrock Classification.
At that time, the field descriptions were confirmed or modified as necessary and an
applicable laboratory testing program was formulated to determine engineering properties
of the subsurface materials. Boring logs were prepared and are presented in Appendix A.
Selected soil and bedrock samples were tested for the following engineering properties:
OA
Geotechnical Engineering Exploration
Lagunitas Company
Terracon Project No. 20955185
• Water content
Dry density
11 Consolidation
• Compressive strength
Terracon
• Expansion
• Plasticity Index
• Water soluble sulfate content
The significance and purpose of each laboratory testis described in Appendix C. Laboratory
test results are presented in Appendix B, and were used for the geotechnical engineering
analyses, and the development of foundation and earthwork recommendations. All
laboratory tests were performed in general accordance with the applicable ASTM, local or
other accepted standards.
SITE CONDITIONS
The site is located in Cameron Park. Several office buildings exist on the site. These
buildings consist of masonry and wood frame structures. The area is vegetated with grass,
Russian olive trees, and cottonwood trees. Drainage is generally positive to the east except
along the west edge of the site which drains to the west toward a small stream that ponds
directly west of the site. The site is bordered on the north by existing residences and open
land, to the east by the South College Avenue frontage road and office buildings and to the
south by existing office buildings. Small piles of fill were noted on the site where soil,
concrete and rock have been placed. A large outcrop of sandstone is located in the
southeast corner of the pond west of the site.
SUBSURFACE CONDITIONS
Geology: The proposed area is located within the Colorado Piedmont section of the Great
Plains physiographic province. The Colorado Piedmont, formed during Late Tertiary and
Early Quaternary time (approximately 2,000,000 years ago), is a broad, erosional trench
which separates the Southern Rocky Mountains from the High Plains. Structurally, the site
lies along the western flank of the Denver Basin. During the Late Mesozoic and Early
Cenozoic Periods (approximately 70,000,000 years ago), intense tectonic activity occurred,
causing the uplifting of the Front Range and associated downwarping.of the Denver Basin
to the east. Relatively flat uplands and broad valleys characterize the present-day
topography of the Colorado Piedmont in this region. The site is underlain by the Cretaceous
Pierre Formation. The Pierre formation in this area consists of sandstone which was
encountered at depths of '/: to 1 1'/s feet below the surface. The bedrock is overlain by
residual and alluvial clays and sands of Pleistocene and/or Recent Age.
3
Geotechnical Engineering Exploration Terracon
Lagunitas Company
Terracon Project No. 20955185
Mapping completed by the Colorado Geological Survey ('Hart, 1972), indicates the site in
an area of "Low Swell Potential." Potentially expansive materials mapped in this area
include bedrock, weathered bedrock and colluvium (surficial units).
Soil and Bedrock Conditions: The following describes the characteristics of the primary soil
strata in order of increasing depths:
• Silty Topsoil and Fill Material: The majority of the area tested is overlain by a 6-inch
layer of silty topsoil. The topsoil has been penetrated by root growth and organic
matter. A 1 to 5 foot layer of fill material was encountered at the surface of Borings
6, 8, 10 and 11. The fill consists of sandy lean clay with gravel, bedrock fragments
and debris such as wood, wire, concrete, and organic matter.
• Clayey and/or Silty Sand: This stratum was encountered at the surface of Borings
3 and 12 through 16 and extends to the bedrock below. The sand varies from
clayey to a silty sand, is nonplastic to slightly plastic and loose to medium dense in
its moist condition.
• Sandy Lean Clay: This stratum was encountered in Borings 1, 2, 4 through 11 and
17 below the topsoil and/or fill and extends to the bedrock below. The lean clay
varies from sandy lean clay to lean clay with sand, is dry to wet and medium to very
stiff in consistency.
• Sandstone Bedrock: The bedrock was encountered in all borings at depths of %2 to
- - - 1 1'h-feet. and extends to greater depths. The upper '/2 to 2 feet of the bedrock is
highly weathered, however, the underlying sandstone is well cemented. Lenses of --
densely cemented sandstone was encountered in Borings 2, 3, 4, 8, and 11 at
depths of 6 to 17 feet.
Field and Laboratory Test Results: Field and laboratory test results indicate the sand soils
are loose to medium dense and exhibit generally moderate bearing characteristics. The clay
soils are medium to.very stiff and exhibit generally moderate bearing characteristics and low
swell potential. The bedrock exhibits very high bearing characteristics and non to low swell
potential.
'Hart, Stephen S., 1972, Potentially Swelling Sal and Rock in the Front Range Urban Corridor, Colorado, Colorado
Geological Survey, Environmental Geology No. 7.
H