HomeMy WebLinkAboutMANHATTAN TOWNHOMES - PDP - 34-04 - SUBMITTAL DOCUMENTS - ROUND 1 - RECOMMENDATION/REPORTGeotechnical Engineering Report lrerracon
Proposed Townhome Development — 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
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design and specifications. Terracon also should be retained to provide testing and observation
during excavation, grading, foundation and construction phases of the project.
The analysis and recommendations presented in this report are based upon the data obtained
from the borings performed at the indicated locations and from other information discussed in this
report. This report does not reflect variations that may occur between borings, across the site, or
due to the modifying effects of weather. The nature and extent of such variations may not
become evident until during or after construction. If variations appear, we should be immediately
notified so that further evaluation and supplemental recommendations can be provided.
The scope of services for this project does not include either specifically or by implication any
environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or
prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the
potential for such contamination or pollution, other studies should be undertaken.
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 generally accepted geotechnical
engineering practices. No warranties, either express or implied, are intended or made. Site
safety, excavation support, and dewatering requirements are the responsibility of others. In the
event that changes in the nature, design, or location of the project as outlined in this report are
planned, the conclusions and recommendations contained in this report shall not be considered
valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this
report in writing.
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Geotechnical Engineering Report Irerracon
Proposed Townhome Development - 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
• using designs which allow vertical movement between the exterior features and
adjoining structural elements
• placing effective control joints on relatively close centers
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 imported material approved by the geotechnical engineer. The pipe backfill
should be compacted to a minimum of 95 percent of Standard Proctor Density ASTM
_ D698.
Surface Drainage
Positive drainage should be provided during construction and maintained throughout the
life of the proposed project. 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. 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.
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. Sprinkler systems should not be installed within 10-feet of foundation walls.
Landscaped irrigation adjacent to the foundation system should be minimized or
eliminated.
GENERAL COMMENTS
Terracon should be retained to review the final design plans and specifications so comments can
be made regarding interpretation and implementation of our geotechnical recommendations in the
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Geotechnical Engineering Report lrerracon
Proposed Townhome Development - 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
the lift. It is recommended all fill material to placed on the site be compacted to at least
95 percent of Standard Proctor Density ASTM D698.
On -site clay soils should be compacted within a moisture content range of 1 percent
I below, to 3 percent above optimum. Imported granular soils should be compacted within a
moisture range of 3 percent below to 3 percent above optimum unless modified by the
' project geotechnical engineer.
Excavation and Trench Construction
Excavations into the on -site soils will encounter a variety of conditions. Excavations into
the clays can be expected to stand on relatively steep temporary slopes during
' construction. However, caving soils and 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.
The soils to be penetrated by the proposed excavations may vary significantly across the
site. The preliminary soil classifications are based solely on the materials encountered in
widely spaced exploratory test borings. The contractor should verify that similar conditions
exist throughout the proposed area of excavation. If different subsurface conditions are
encountered at the time of construction, the actual conditions should be evaluated to
determine any excavation modifications necessary to maintain safe conditions.
As a safety measure, it is recommended that all vehicles and soil piles be kept to a
minimum lateral distance from the crest of the slope equal to no less than the slope height.
The exposed slope face should be protected against the elements.
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
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Geotechnical Engineering Report
Proposed Townhome Development — 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
lrerracon
Based upon the subsurface conditions determined from the geotechnical exploration, the
majority of the underlying subgrade soils exposed during construction are anticipated to be
relatively stable; however soft compressible and/or unstable areas may be encountered
during construction, especially in close proximity to the groundwater. The stability of the
subgrade may be affected by precipitation, repetitive construction traffic or other factors. If
unstable conditions develop, workability may be improved by scarifying and drying.
Overexcavation of wet zones and replacement with granular materials may be necessary.
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. Lightweight excavation
equipment may be required to reduce subgrade pumping.
Subgrade Preparation
Subgrade soils beneath interior and exterior slabs, and beneath pavements should be
scarified, moisture conditioned and compacted to a minimum depth of 12-inches below
proposed controlled fill material. The moisture content and compaction of subgrade soils
should be maintained until slab or pavement construction.
Fill Materials and Placement
Approved imported materials may be used as fill material and are suitable for use as
compacted fill beneath interior or exterior floor slabs.
Imported soils (if required) should conform to the following:
Gradation
Percent finer by weight
(ASTM C136)
3.................................................................................................
.......... 100
No. 4 Sieve..................................................................................... 50-100
No. 200 Sieve.............................................................................. 65 (max)
• Liquid Limit..................................................................................
30 (max)
• Plasticity Index.............................................................................
15 (max)
• Group Index.................................................................................
10 (max)
Engineered fill should be placed and compacted in horizontal lifts, using equipment and
procedures that will produce recommended moisture contents and densities throughout
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Geotechnical Engineering Report lerracon
Proposed Townhome Development — 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
maintenance activities are intended to slow the rate of pavement deterioration, and to preserve
the 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. Prior to implementing any maintenance,
additional engineering observation is recommended to determine the type and extent of
preventative maintenance.
1 Earthwork
General Considerations
The following presents recommendations for site preparation, excavation, subgrade
preparation and placement of engineered fills on the project.
All earthwork on the project should be observed and evaluated by Terracon. The
evaluation of earthwork should include observation and testing of engineered fill, subgrade
preparation, foundation bearing soils, and other geotechnical conditions exposed during
the construction of the project.
Site Preparation
Strip and remove any existing debris or other deleterious materials from proposed building
areas. All exposed surfaces should be free of mounds and depressions that could prevent
uniform compaction.
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 fill areas.
All exposed areas which will receive fill, once properly cleared and benched where
necessary, should be scarified to a minimum depth of 12-inches and conditioned to the
moisture contents outlined under the "Fill Materials and Placement' section of this report.
It is anticipated that excavations for the proposed construction can be accomplished with
conventional earthmoving equipment.
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Geotechnical Engineering Report
Proposed Townhome Development - 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
1rerraron
In addition to the flexible pavement design analyses, a rigid pavement design analysis was
completed, based upon AASHTO design procedures. Rigid pavement design is based on an
evaluation of the Modulus of Subgrade Reaction of the soils (K-value), the Modulus of Rupture of
the concrete, and other factors previously outlined. The design K-value of 100 for the subgrade
soil was determined by correlation to the laboratory tests results. A modulus of rupture of 650 psi
(working stress 488 psi) was used for pavement concrete. The rigid pavement thicknesses for
each traffic Category were determined on the basis of the AASHTO design equation.
Recommended Pavement Thicknesses (Inches)
Asphalt Concrete
Aggregate
Asphalt Concrete
Portland
Traffic Area
Alternative
Surface-
Base
Surface-
Cement
TOTAL
Grading S or SX
Course
Grading S or SG
Concrete
Automobile
A
3Y�
6
9Yz
Parking
g
5Y:
5%2
Main Traffic
A
4
8
12
Corridors
g
6
6
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 park and load.
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 not exceeding 6-
inches and should be compacted to a minimum of 95% Standard Proctor Density (ASTM D698).
Asphalt concrete should be composed of a mixture of aggregate, filler and additives, if required,
and approved bituminous material. The asphalt concrete should conform to approved mix
designs stating the Hveem and/or Superpave properties, optimum asphalt content, job mix
formula and recommended mixing and placing temperatures. Aggregate used in asphalt concrete
should meet particular gradations meeting Colorado Department of Transportation Grading S, SX
or SG specifications. 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 92 to 96 % of Maximum Theoretical Density.
Preventative maintenance should be planned and provided for through an on -going pavement
management program in order to enhance future pavement performance. Preventative
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�. Geotechnical Engineering Report lrerracon
Proposed Townhome Development - 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
• A minimum 2-inch void space should be constructed above, or below non -
bearing partition walls placed on the floor slab. Special framing details should be
provided at door jambs and frames within partition walls to avoid potential
distortion. Partition walls should be isolated from suspended ceilings.
Interior trench backfill placed beneath slabs should be compacted in accordance
' with recommended specifications outlined below.
• In areas subjected to normal loading, a minimum 6-inch layer of clean -graded
gravel, aggregate base course should be placed beneath interior slabs.
• Floor slabs should not be constructed on frozen subgrade.
• Other design and construction considerations, as outlined in the ACI Design
Manual, Section 302.1 R are recommended.
Pavement Design and Construction
Design of pavements for the project have been based on the procedures outlined in the 1993
Guideline for Design of Pavement Structures by the American Association of State Highway and
Transportation Officials (AASHTO). Areas within proposed pavements on the site will be divided
into two categories based upon anticipated traffic and usage.
Traffic criteria provided for pavement thickness designs are estimated by Terracon based on
similar projects and are to include single 18-kip equivalent single axle loads (ESAL's) of 51,100 for
automobile parking, and 146,000 for heavy volume and/or truck access areas.
Local drainage characteristics of proposed pavement areas are considered to vary from fair to
good depending upon location on the site. For purposes of this design analysis, fair drainage
characteristics are considered to control the design. These characteristics, coupled with the
approximate duration of saturated subgrade conditions, result in a design drainage coefficient of
1.0 when applying the AASHTO criteria for design.
' For flexible pavement design, a terminal serviceability index of 2.0 was utilized along with an
inherent reliability of 70%, and a design life of 20 years. Using an estimated design R-value
estimated at 7 based on the group index/soil classification values, appropriate ESAL/day,
environmental criteria and other factors, the structural numbers (SN) of the pavement sections
were determined on the basis of the 1993 AASHTO design equation.
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Geotechnical Engineering Report lrerracon
Proposed Townhome Development — 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
Fill against grade beams and retaining walls should be compacted to densities specified in
Earthwork. Compaction of each lift adjacent to walls should be accomplished with hand -operated
tampers or other lightweight compactors. Overcompaction may cause excessive lateral earth
pressures, which could result in wall movement.
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 1997 Uniform Building Code. Based upon the nature of the subsurface materials,
a soil profile type Sc should be used for the design of structures for the proposed project (1997
Uniform Building Code, Table No. 16-JF000r Slab Design and Construction.
Floor Slab Design and Construction
The variability of the existing soils at approximate slab subgrade elevation could result in
differential movement of floor slab -on -grade should expansive soils become elevated in
moisture content. If slab movement cannot be tolerated, use of structural floor systems,
structurally supported independent of the subgrade soils, is a positive means of eliminating the
potentially detrimental effects of floor movement and are recommended.
If conventional slab on grade construction is utilized in conjunction with the drilled
' piers/caissons, it is recommended that there be a minimum of 4-feet of moisture controlled fill
material placed and compacted beneath all slabs. This will require over -excavation of the
moderately expansive overburden clays and bedrock material and replacement with moisture
controlled fill material. To accommodate this, it is recommended the clay soils be over -
excavated to a minimum depth of 3-feet below slab elevations and stockpiled for reuse. The
clay soils should then be moisture conditioned to 1-percent below optimum moisture content to
3-percent above of optimum moisture, placed in uniform lifts and compacted to at least 95
percent of Standard Proctor Density ASTM D698 to final slab subgrade elevations. This
alternative will not eliminate the possibility of slab heave; but movements should be reduced
and tend to be more uniform.
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.
• Control joints should be provided in slabs to control the location and extent of
cracking.
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Geotechnical Engineering Report lrerracon
Proposed Townhome Development — 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
Due to potential sloughing and raveling, foundation concrete quantities may exceed calculated
geometric volumes. Pier concrete with slump in the range of 6 to 8 inches is recommended.
If casing is used for pier construction, it should be withdrawn in a slow continuous manner
maintaining a sufficient head of concrete to prevent infiltration of water or the creation of voids in
pier concrete. Pier concrete should have relatively high fluidity when placed in cased pier holes or
through a tremie.
To provide increased resistance to potential uplift forces, the sides of each pier should be
' mechanically roughened in the bearing strata below a depth of 10-feet. This should be
accomplished by a roughening tooth placed on the auger. Pier bearing surfaces must be cleaned
prior to concrete placement. A representative of the geotechnical engineer should inspect the
bearing surface and pier configuration.
Lateral Earth Pressures
For soils above any free water surface, recommended equivalent fluid pressures for unrestrained
foundation elements are:
1 Active:
Cohesive soil backfill (on -site clay).........................................45 psf/ft
On -site bedrock materials ...........................not recommended for use
• Passive:
Cohesive soil backfill (on -site clay).......................................250 psf/ft
Undisturbed bedrock.............................................................450 psf/ft
' Where the design includes restrained elements, the following equivalent fluid pressures are
recommended:
• At rest:
Cohesive soil backfill (on -site clay).........................................60 psf/ft
On -site bedrock materials ........................... not recommended for use
1 The lateral earth pressures herein do not include any factor of safety and are not applicable for
submerged soils/hydrostatic loading. Additional recommendations may be necessary if
submerged conditions are to be included in the design.
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Geotechnical Engineering Report
Proposed Townhome Development - 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
lrerraran
diameter of 12-inches is recommended. A minimum 4-inch or greater void space should be
provided beneath grade beams between piers. The void material should be of suitable strength to
support the weight of fresh concrete used in grade beam construction, and to avoid collapse when
foundation backfill is placed.
Required pier penetration should be balanced against potential uplift forces due to expansion of
the subsoils and bedrock on the site. For design purposes, the uplift force on each pier can be
determined on the basis of the following equation:
' Up=20xD
Where: Up = the uplift force in kips, and
D = the pier diameter in feet
Uplift forces on piers should be resisted by a combination of dead load and pier penetration below
a depth of 10-feet and in the bearing strata.
To satisfy forces in the horizontal direction, piers may be design for lateral loads using a modulus
of 75 tons per square foot for the portion of the pier in clays, weathered siltstone/claystone
bedrock and/or engineered fill, and 400 tsf in competent bedrock for a pier diameter of 12 inches.
The coefficient of subgrade reaction for varying pier diameters is as follows:
Pier Diameter
(inches)
Coefficient of Subgrade Reaction (tons/ft3)
Engineered Fill or
Stiff Clays
Bedrock
12
75
400
18
50
267
24
38
200
30
30
160
36
25
133
The soil modulus and coefficient of subgrade reaction are ultimate values; therefore, appropriate
factors of safety should be applied in the pier design.
Shafts will probably remain open without stabilizing measures. However, pier concrete should be
placed soon after completion of drilling and cleaning. Groundwater was encountered during the
drilling exploration; therefore, temporary casing may be required. Groundwater, if encountered
during drilling operations, should be removed from each pier hole prior to concrete placement. A
maximum 3-inch depth of groundwater is acceptable in each pier prior to concrete placement. If
pier concrete cannot be placed in dry conditions, a tremie should be used for concrete placement.
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Geotechnical Engineering Report lrerracon
Proposed Townhome Development — 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
Foundation Systems — Conventional Spread Footings
Spread footing foundations placed a minimum of 3-feet above the moderately expansive
siltstone/claystone bedrock formation and bearing on the native undisturbed subsoils and/or
engineered fill material, may be used to support the proposed townhome and/or garage structures
for at the site. Footings should be designed for a net allowable bearing pressure of 2,000 psf. In
addition, all footings should be sized to maintain a minimum dead load pressure of 500 psf. If
footings cannot be placed a minimum of 3-feet above the bedrock stratum due to design
elevations, then a drilled pier foundation system should be utilized.
Exterior footings should be placed a minimum of 30 inches below finished grade for frost
protection and to provide confinement for the bearing soils. Finished grade is the lowest adjacent
1 grade for perimeter footings.
Footings should be proportioned to reduce differential foundation movement. Proportioning on
' the basis of equal total movement is recommended; however, proportioning to relative constant
dead -load pressure will also reduce differential movement between adjacent footings. Total
movement resulting from the assumed structural loads is estimated to be on the order of 1-inch or
less. Additional foundation movements could occur if water from any source infiltrates the
foundation soils; therefore, proper drainage should be provided in the final design and during
construction.
Foundation Systems — Drilled Piers/Caissons
Due to the moderately expansive bedrock materials encountered near basement elevations, a
grade beam and drilled pier/caisson foundation system is recommended to support any structure
within the 3-feet of the bedrock formation. Straight shaft piers, drilled a minimum of 8-feet into
competent or harder bedrock, with minimum shaft lengths of 20-feet are recommended.
For axial compression loads, piers may be design for a net allowable end -bearing pressure of
15,000 pounds per square foot (psf), and skin friction of 1,500 psf for the portion of the pier in firm
or harder bedrock. Piers should be designed for a minimum dead -load pressure of 5,000 psf,
based upon pier end area.
All piers should be reinforced full depth for the applied axial, lateral and uplift stresses imposed.
The amount of reinforcing steel for expansion should be determined by the tensile force created
by the uplift force on each pier, with allowance for dead load.
To reduce potential uplift forces on piers, use of long grade beam spans to increase individual pier
loading, and small diameter piers are recommended. For this project, use of a minimum pier
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Geotechnical Engineering Report lferracon
Proposed Townhome Development — 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
Groundwater Conditions
Groundwater was encountered at an approximate depth of 9 to 14-feet below existing site
grades in each test boring when checked on July 27, 2004. These observations represent
groundwater conditions at the time of the field exploration, 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.
Zones of perched and/or trapped groundwater may occur at times in the subsurface soils
overlying bedrock, on top of the bedrock surface or within permeable fractures in the bedrock
materials. The location and amount of perched water is dependent upon several factors, including
hydrologic conditions, type of site development, irrigation demands on or adjacent to the site,
fluctuations in water features, seasonal and weather conditions.
ENGINEERING ANALYSES AND RECOMMENDATIONS
Geotechnical Considerations
The site appears suitable for the proposed construction from a geotechnical engineering point of
view.
The following foundation system was evaluated for use on the site for the proposed structures:
• Conventional type spread footings bearing upon the undisturbed subsoils, or engineered fill
' material and placed a minimum of 3-feet above the bedrock formation; and
• Grade beams and straight shaft piers/caisson drilled into the bedrock.
' If floor movement cannot be tolerated, use of a structural floor system should be utilized. If slab -
on -grade construction is utilized for lower level construction, over -excavation of the bedrock
formation to allow for a minimum 4-foot separation between floor slab and the undisturbed
bedrock is recommended.
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 significantly from those presented in this report, supplemental
recommendations will be required.
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Geotechnical Engineering Report lferracon
Proposed Townhome Development — 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
Laboratory tests were conducted on selected soil and bedrock samples and are presented in
' Appendix B. The test results 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 local or other accepted standards.
Selected soil and bedrock samples were tested for the following engineering properties:
• Water Content
• Dry Density
• Swell — Consolidation
• Atterberg Limits/Soil Classifications
SITE CONDITIONS
The site is located on the east side of Manhattan Avenue, south of the existing Manhattan Min -
Storage Project, and southwest of the Carmike Theatres in Fort Collins, Colorado. An existing 2-
story apartment complex is situated within the central portion along the south side of the site. The
New Mercer Canal meanders along the eastern boundary of the site. The site is relatively flat
exhibiting positive surface drainage in the southeast direction.
SUBSURFACE CONDITIONS
Soil and Bedrock Conditions
An approximate 6 to 8-inch layer of silty topsoil was encountered at the surface of each boring.
' Underlying the topsoil was native cohesive clay strata; classified as lean clay, lean clay with sand
and/or sandy lean clay, which extended extending to the bedrock below. Siltstone/claystone
' bedrock with intermittent well cemented siltstone/sandstone lenses was encountered at
approximate depths of 6 to 11-feet below existing site grades and extended to the depths
explored, approximately 25-feet.
Field and Laboratory Test Results
Field and laboratory test results indicate the clay soils are medium stiff to very stiff in consistency
and exhibits low to moderate bearing characteristics. The bedrock stratum varies from
moderately hard to hard with increasing depths and exhibits a low swell potential and moderate to
' high bearing characteristics.
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Geotechnical Engineering Report lrerracon
Proposed Townhome Development - 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
SITE EXPLORATION
The scope of the services performed for this project included a site reconnaissance by an
engineering geologist, a subsurface exploration program, laboratory testing and engineering
analyses.
Field Exploration
A total of 3 test borings were drilled on July 16, 2004 at the locations shown on the Test Boring
Location Diagram, Figure 1. The test borings were located within the footprints of the proposed
townhome structures and were drilled to approximate depths of 15 to 25-feet. The borings were
advanced with a truck -mounted drilling rig, utilizing 4-inch diameter solid stem augers.
The borings were located in the field by pacing from existing site features. Approximate ground
surface elevations were determined at each boring location by interpolating between contours on
the topographic map provided to us by the client and are shown on the enclosed log of borings.
The accuracy of boring locations and elevations should only be assumed to the level implied by
the methods used.
Lithologic logs of each boring were recorded by the engineering geologist during the drilling
operations. At selected intervals, samples of the subsurface materials were taken by means of
pushing thin -walled Shelby tubes, or by driving split -spoon and ring barrel samplers.
Penetration resistance measurements were obtained by driving the split -spoon and ring barrel into
the subsurface materials with a 140-pound hammer falling 30 inches. The penetration resistance
value is a useful index in estimating the consistency, relative density or hardness of the materials
encountered.
Groundwater conditions were evaluated in each boring at the time of site exploration and on July
27. 2004.
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 general accordance with the Unified Soil
Classification System described in Appendix C. Samples of bedrock were classified in general
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.
2
GEOTECHNICAL ENGINEERING REPORT
' PROPOSED TOWNHOME DEVELOPMENT PROJECT
3836 MANHATTAN AVENUE
FORT COLLINS, COLORADO
' TERRACON PROJECT NO. 20045114
AUGUST 2, 2004
INTRODUCTION
■ This report contains the results of our supplemental geotechnical engineering exploration for the
proposed 5 building townhome development project to be located at 3836 Manhattan Avenue,
' south of the existing Manhattan Avenue Mini -Storage facility in Fort Collins, Colorado. The project
is to consist of 2, 8-unit buildings, 2, 5-unit buildings, 1, 4-unit building, and associated slab on
' grade garage buildings. The site is located in the East ''/z of Section 35, Township 7 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
e groundwater conditions
' • foundation design and construction
• floor slab design and construction
• pavement design and construction
• earthwork
• drainage
The recommendations contained in this report are based upon the results of field and laboratory
' testing, engineering analyses, and experience with similar soil conditions, structures and our
understanding of the proposed project.
' PROPOSED CONSTRUCTION
It is Terracon's understanding the project will consist of 5, 2-story townhome buildings. The
buildings will consist of 2, 8-unit structures, 2, 5-unit structures and 1, 4-unit townhome structure,
along with lightly loaded single story slab on grade garage buildings, and associated parking and
' drive areas. The anticipated maximum wall and columns loads for the project are 1 to 4 klf and 10
to 75 kips, respectively. Although final site grading plans were not available at the time of the field
exploration, it is assumed finished floor levels will be at or slightly above existing site grades.
TABLE OF CONTENTS
'
Page No.
Letterof Transmittal...................................................................................................
i
INTRODUCTION.............................................................................................................................1
PROPOSEDCONSTRUCTION......................................................................................................1
SITEEXPLORATION......................................................................................................................2
Field Exploration....................................................................................................................2
'
LaboratoryTesting.................................................................................................................2
SITECONDITIONS.........................................................................................................................3
SUBSURFACECONDITIONS........................................................................................................3
Soil and Bedrock Conditions.................................................................................................3
Field and Laboratory Test Results........................................................................................3
GroundwaterConditions........................................................................................................4
ENGINEERING ANALYSES AND RECOMMENDATIONS...........................................................4
' Geotechnical Considerations.................................................................................................4
Foundation Systems — Conventional Spread Footings.........................................................5
Foundation Systems — Drilled Piers/Caissons......................................................................5
' Lateral Earth Pressures.........................................................................................................7
Seismic Considerations.........................................................................................................8
Floor Slab Design and Construction...................................................................................8
Pavement Design and Construction......................................................................................8
'
Earthwork.............................................................................................................................11
General Considerations.............................................................................................11
SitePreparation...................................................................................................I......11
SubgradePreparation................................................................................................12
Fill Materials and Placement.....................................................................................12
Excavation and Trench Construction........................................................................13
' Additional Design and Construction Considerations...........................................................13
Exterior Slab Design and Construction.....................................................................13
Underground Utility Systems.....................................................................................14
' Surface Drainage.......................................................................................................14
GENERALCOMMENTS...............................................................................................................14
APPENDIX A
Boring Location Diagram
Logs of Borings
' APPENDIX B
Laboratory Test Results
APPENDIX C
General Notes
Geotechnical Engineering Report lrerracon
Proposed Townhome Development — 3836 Manhattan Avenue
Fort Collins, Colorado
Project No. 20045117
slab on grade construction, this requirement should be achievable; however, if basements are
being considered, a drilled_ pier foundation system is recommended. For the lightly loaded
garage type structures situated along the southeastern portion of the site, spread footings
should be feasible. For those buildings in which the foundation systems are to be within 3-feet
of the bedrock, a grade beam and straight shaft drilled pier foundation system should be
utilized.
In conjunction with drilled piers/caissons for lower level construction, if slab movement cannot
be tolerated, a structural floor system is recommended. If conventional slab on grade
construction is utilized for any lower levels it is recommended that there be a minimum of 4-feet
of moisture controlled fill material placed and compacted beneath all slabs. This will require
over -excavation of the bedrock materials and replacement with moisture controlled .fill material.
To accommodate this, it is recommended the clay soils and underlying bedrock formation, be
over -excavated to allow for a minimum separation of 4-feet below slab elevations and
undisturbed bedrock. The over excavated zone should then be replaced with a non to low
expansive, moisture conditioned approved fill material, placed in uniform lifts and compacted to
at least 95 percent of Standard Proctor Density ASTM D698 to final slab subgrade elevations.
This alternative will not eliminate the possibility of slab heave; but movements should be
reduced and tend to be more uniform. Conventional type slab on grade construction is feasible
for upper level floor slabs.
Other design and construction recommendations, based upon geotechnical conditions, are
presented in the report.
We appreciate being of service to you in the geotechnical engineering phase of this project,
and are prepared to assist you during the construction phases as well. If you have any
questions concerning this report or any of our testing, inspection, design and consulting
services please do not hesitate to contact us.
Sincerely, �po0 RfC`V
TERRACON o�� •• A••• �f
a 12
David A. Richer, P. j�j' ;•••''G�
Geotechnical Engineer%D.epart �t
Copies to: (5) Addressee
r
oug J. Ie, .E.
Manager Regional Manager
August 3, 2004
Lagunitas Companies
3944 JFK Parkway
Fort Collins, Colorado 80525
Attn: Mr. Jon Prouty
Irerracon
301 N. Howes • P.O. Box 503
Fort Collins, Colorado 80521-0503
(970) 484-0359 Fax: (970) 484-0454
Re: Geotechnical Engineering Report
Proposed 5-Building Townhome Development Project
3836 Manhattan Avenue — South of Manhattan Mini -Storage Facility
Fort Collins, Colorado
Terracon Project No. 20045117
Terracon has completed a geotechnical engineering exploration for the proposed 5 building
townhome development project to be located at 3836 Manhattan Avenue, south of the existing
Manhattan Avenue Mini -Storage facility in Fort Collins, Colorado. The project is to consist of 2,
8-unit buildings, 2, 5-unit buildings, 1, 4-unit building, and associated slab on grade garage
buildings. This study was completed in general accordance with our Proposal No. D2004252
dated July 9, 2004.
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, pavements and other earth connected phases of this project
are attached.
' An approximate 6 to 8-inch layer of silty topsoil was encountered at the surface of each boring.
Underlying the topsoil was native cohesive clay strata; classified as lean clay, lean clay with
sand and/or sandy lean clay, which extended extending to the bedrock below.
Siltstone/claystone bedrock with intermittent well cemented siltstone/sandstone lenses was
encountered at approximate depths of 6 to 11-feet below existing site grades and extended to
the depths explored, approximately 25-feet. Groundwater was encountered at approximate
' depths of 9 to 14-feet below existing site grade in the test borings when checked on July 27,
2004.
The results of field exploration and laboratory testing completed for this study indicate the
soils and bedrock at the site have low expansive potential, and exhibit low to moderate load
' bearing capabilities.
Based on the subsurface conditions encountered and the type on construction proposed, the
proposed townhome structures could be supported by conventional type spread footings if the
bottom of the foundations are placed a minimum of 3-feet above the bedrock formation. For
J
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Quality Engineering Since 1965
GEOTECHNICAL ENGINEERING REPORT
PROPOSED TOWNHOME DEVELOPMENT PROJECT
3836 MANHATTAN AVENUE
FORT COLLINS, COLORADO
TERRACON PROJECT NO. 20045114
AUGUST 3, 2004
Prepared for.
LAGUNITAS COMPANIES
3944 JFK PARKWAY
FORT COLLINS, COLORADO 80525
ATTN: MR. JON PROUTY
Prepared by.
Terracon
301 North Howes Street
Fort Collins, Colorado 80521
Irerracon