HomeMy WebLinkAboutB12-0585 810106 Geotechnical Report09-06-12Geotechnical Engineering Report
AT&T Vail – Site 810106
1309 Elkhorn Drive
Vail, Colorado
September 6, 2012
Terracon Project No. 25125082
Prepared for:
ATECS, LLC
Golden, Colorado
Prepared by:
Terracon Consultants, Inc.
Wheat Ridge, Colorado
B12-0585
September 6, 2012
ATECS, LLC
16360 Table Mountain Parkway
Golden, CO 80403
Attn: Mr. Glenn Bernard
E: Glennb@atecs.com
Re: Geotechnical Engineering Report
AT&T Vail – Site 810106
1309 Elkhorn Drive
Vail, Colorado
Terracon Project No: 25125082
Mr. Bernard:
Terracon Consultants, Inc. (Terracon) has performed the geotechnical engineering services for
the above referenced project. This study was performed in general accordance with the
purchase order, PO/WO #344 dated August 31, 2012 and the master services agreement dated
March 14, 2011. This report presents the findings of the subsurface exploration and provides
geotechnical recommendations concerning earthwork and the design of foundations for the
proposed monopole and equipment shelter.
We appreciate the opportunity to be of service to you on this project. If you have any questions
concerning this report, or if we may be of further service, please contact us.
Sincerely,
TERRACON CONSULTANTS, INC.
Scott B. Myers, P.E.
Geotechnical Department Manager
Thomas J. Nevin, P.E.
Senior Project Engineer
Copies to: Addressee (PDF)
Terracon Consultants, Inc. 10625 W. I -70 Frontage Rd N, Ste 3 Wheat Ridge, Colorado 80033
P [303] 423 -3300 F [303] 423 -3353 www.terracon.com
33822
9/6/12
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
TABLE OF CONTENTS
EXECUTIVE SUMMARY ............................................................................................................. i
1.0 INTRODUCTION ............................................................................................................. 1
2.0 PROJECT INFORMATION ............................................................................................. 1
2.1 Project Description .............................................................................................. 1
2.2 Site Location and Description ............................................................................. 2
3.0 SUBSURFACE CONDITIONS ........................................................................................ 2
3.1 Typical Profile ...................................................................................................... 2
3.2 Groundwater ....................................................................................................... 3
4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION ...................................... 3
4.1 Geotechnical Considerations ................................................................................ 3
4.1.1 Existing Fill ............................................................................................... 4
4.1.2 Structural Design Considerations ............................................................. 4
4.2 Earthwork ........................................................................................................... 4
4.2.1 Site Preparation ....................................................................................... 4
4.2.2 Material Types .......................................................................................... 5
4.2.3 Compaction Requirements ....................................................................... 5
4.2.4 Grading and Drainage ............................................................................... 6
4.2.5 Construction Considerations ...................................................................... 6
4.3 Foundation Recommendations ........................................................................... 7
4.3.1 Monopole Foundation Design Recommendations .................................... 7
4.3.2 Monopole Foundation Construction Considerations ................................. 8
4.3.3 Equipment Shelter Design Recommendations ......................................... 9
4.3.4 Equipment Shelter Construction Considerations .....................................10
4.4 Seismic Considerations......................................................................................10
4.5 Corrosion Protection ..........................................................................................11
5.0 GENERAL COMMENTS ............................................................................................... 11
APPENDIX A – FIELD EXPLORATION
Exhibit A-1 Field Exploration Description
Exhibit A-2 Boring Location Plan
Exhibit A-3 Boring Log
APPENDIX B – LABORATORY TESTING
Exhibit B-1 Laboratory Testing Description
Exhibit B-2 Grain Size Distribution
Exhibit B-3 Summary of Laboratory Test Results
APPENDIX C – SUPPORTING DOCUMENTS
Exhibit C-1 Explanation of Boring Log Information
Exhibit C-2 Unified Soil Classification System
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
Responsive ■ Resourceful ■ Reliable i
EXECUTIVE SUMMARY
A geotechnical engineering report has been prepared for the proposed monopole and equipment
shelter to be located at 1309 Elkhorn Drive in Vail, Colorado. One boring was advanced to a depth
of about 21 feet below the existing ground surface at the proposed monopole and equipment
shelter location. The following geotechnical considerations were identified:
A drilled shaft foundation system is considered suitable for support of the proposed
monopole. The use of straight shaft piers drilled with a minimum shaft length of 15 feet
is recommended. Alternatively, the monopole could be supported by a spread footing if
the owner is willing to accept some additional risk of movement.
About 10 feet of existing fill was encountered in the exploratory boring and will be
present below the proposed equipment shelter. There is risk of movement for
improvements constructed on undocumented fill. To improve performance and provide
more uniform support, 3 feet of the fill below the proposed shelter could be modified and
replaced as new engineered fill.
Assuming proper site preparation, total movement for the equipment shelter is estimated
to be on the order of 1to 2 inches or more and differential movement about ½ to ¾ of the
total.
The 2009 International Building Code, Table 1613.5.2 IBC seismic site classification for
this site is D.
This summary should be used in conjunction with the entire report for design purposes. It should
be recognized that details were not included or fully developed in this section, and the report must
be read in its entirety for a comprehensive understanding of the items contained herein. The
section titled GENERAL COMMENTS should be read for an understanding of the report
limitations.
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GEOTECHNICAL ENGINEERING REPORT
AT&T VAIL – SITE 810106
1309 ELKHORN DRIVE
VAIL, COLORADO
Terracon Project No. 25125082
September 6, 2012
1.0 INTRODUCTION
A geotechnical engineering report has been prepared for the proposed monopole and equipment
shelter to be located at 1309 Elkhorn Drive in Vail, Colorado. One boring was advanced to a depth
of about 21 feet below the existing ground surface in the proposed monopole and equipment
shelter location. A Boring Log along with a Boring Location Plan is included in Appendix A of this
report.
The purpose of these services is to provide information and geotechnical engineering
recommendations relative to:
subsurface soil and bedrock conditions floor slab design and construction
groundwater levels earthwork
foundation design and construction drainage
2.0 PROJECT INFORMATION
2.1 Project Description
Item Description
Site layout See Appendix A, Exhibit A-2, Boring Location Plan
Proposed construction
We understand a monopole approximately 57 feet tall will be
installed at this site. In addition, an 11-1/2 feet by 20 feet
equipment shelter will also be constructed.
Anticipated foundation systems
Monopole: Drilled pier foundation system
Equipment Building: Shallow spread-footings, bearing about
3 feet below the existing ground surface
Maximum loads Tower: 15 to 30 kips (assumed)
Equipment shelter: 1 to 2 klf (assumed)
Grading Cut and Fill, 3 feet (+/-) max (assumed)
Free-standing retaining walls Not reported as part of site development
Below grade areas Not reported as part of site development
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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2.2 Site Location and Description
Item Description
Location
The proposed monopole and equipment shelter are planned
in the southwest corner of the existing parking lot at 1309
Elkhorn Drive in Vail, Colorado.
Site conditions The site of the proposed construction consists of an existing
parking lot.
Current ground cover Asphalt.
Existing topography
Ground surface in the general area of the proposed
monopole and equipment shelter is flat with an elevation
difference of less than 2 feet.
3.0 SUBSURFACE CONDITIONS
3.1 Typical Profile
Based on the results of the boring, subsurface conditions on the project site can be generalized as
follows:
Material Description
Approximate Depth to
Bottom of Stratum (ft.)
below existing site grade
Density/Hardness
Asphalt About 4 inches N/A
Fill materials consisting of sand
with varying amounts of clay,
gravel and cobbles and lean clay
with varying amounts of gravel
About 10 feet Sand: loose to medium dense
Clay: stiff
Native soils consisting of sand
with varying amounts of clay,
gravel, cobbles and boulders
About 21 feet*,
maximum depth explored Medium dense
* - Practical drill rig refusal likely on a boulder was encountered at a depth of about 21 feet.
Conditions encountered at the boring location are indicated on the individual boring log.
Stratification boundaries on the boring log represent the approximate location of changes in soil;
in-situ, the transition between materials may be gradual. Details for the boring can be found on the
boring log in Appendix A of this report.
Laboratory test results indicate that the fill material and natural sand soils are essentially non-
expansive. The tested samples have the following physical and engineering properties:
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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Boring
No.
Depth
(ft.)
Fines
Content
(%)
Liquid
Limit
(%)
Plasticity
Index
(%)
Expansion/
Consolidation
(%)*
1 7 51 36 13
1 9 43 25 8
Laboratory testing on a soil sample obtained from our boring indicated water a soluble sulfate
concentration of about 1 mg/l, a pH of 8.5 and an electrical resistivity of 4600 ohm-cm. A
summary of the laboratory test results is included in Appendix B.
3.2 Groundwater
At the time of the field exploration, groundwater was not encountered in the exploratory boring
to the maximum depth explored of about 21 feet below the existing ground surface. Due to
safety considerations, the boring was immediately backfilled with auger cuttings following the
completion of drilling operations; therefore, subsequent groundwater measurements were not
obtained. These observations represent groundwater level 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.
Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff
and other factors not evident at the time the boring was performed. Therefore, groundwater
levels during construction or at other times in the life of the structure may be higher or lower
than the level indicated on the boring log. The possibility of groundwater level fluctuations
should be considered when developing the design and construction plans for the project.
4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION
4.1 Geotechnical Considerations
Based on the results of our field investigation, laboratory testing program and geotechnical
analyses, development of the site is considered feasible from a geotechnical viewpoint provided
that the conclusions and considerations provided herein are incorporated into the design and
construction of the project.
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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4.1.1 Existing Fill
Up to about 10 feet of fill was encountered on the subject site. We do not know if the fill was
placed in a controlled manner. If records of fill placement and compaction exist, these should
be provided for our review to confirm the fill is suitable for the proposed construction. If fill
placement and compaction records are unavailable, there is risk of movement for structures
supported on the fill. We understand that an equipment shelter will be constructed as part of the
proposed development. We assume the shelter can tolerate some movement. Provided some
movement is acceptable, the equipment shelter could be constructed on the existing fill. To
provide more uniform support conditions and to improve performance, consideration could be
given to partial modification of the existing fill. Partial modification of existing fill would consist of
removal of 3 feet of fill below the equipment shelter, moisture-conditioning, and replacement of
the fill as new, properly compacted engineered fill. If movement must be minimized the
equipment shelter could be constructed on a drilled pier foundation.
Terracon’s services did not include delineating the horizontal or vertical extent of the existing fill
material. The potential exists for construction debris and/or domestic trash to be encountered
within the fill at this site. Based on our subsurface investigation and our experience in the area,
it is our opinion the potential is low.
We anticipate that the existing fill can be reused for support of the equipment shelter, provided
any deleterious fill materials are removed and some movement can be tolerated. Some
removal and replacement may be required if unsuitable or soft materials are exposed.
4.1.2 Structural Design Considerations
Based on the geotechnical engineering analyses, subsurface exploration and laboratory test
results, the proposed monopole may be supported on drilled pier foundation system. A
concrete slab–on-grade foundation system is considered suitable for support of the proposed
equipment support building, provided the owner is willing to accept some risk of movement. If
the owner is not willing to accept the risk of movement, the proposed equipment shelter should
be supported by a drilled pier foundation system. Design and construction recommendations for
foundation systems and other earth connected phases of the project are outlined herein.
4.2 Earthwork
4.2.1 Site Preparation
Strip and remove existing asphalt, vegetation, unsuitable fills (if encountered) and other
deleterious materials from the proposed construction area. All exposed surfaces should be free
of mounds and depressions that could prevent uniform compaction. Stripped materials
consisting of vegetation, unsuitable fills and organic materials should be wasted from the site or
used to revegetate landscaped areas or exposed slopes after completion of grading operations.
All exposed areas that will receive fill, once properly cleared and benched, should be scarified to
a minimum depth of 12 inches, conditioned to near optimum moisture content and compacted. It
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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is imperative the moisture content of prepared materials be protected from moisture loss.
Additional fills placed on fills previously placed after a period of time should be checked for
moisture content.
Although evidence of unsuitable fills or underground facilities such as septic tanks, cesspools,
basements and utilities was not observed during the site reconnaissance, such features could
be encountered during construction. If significant amounts of unsuitable fills or underground
facilities are encountered, such features should be removed and the excavation thoroughly
cleaned prior to backfill placement and/or construction.
4.2.2 Material Types
Clean on-site soils, existing fill or approved imported materials may be used as fill material for
this project. Imported soils (if required) should meet the following material property
requirements:
Gradation Percent finer by weight (ASTM C136)
6” 100
3” 70-100
No. 4 Sieve 50-100
No. 200 Sieve 20-70 (max)
Liquid Limit……………………………………………………30 (max)
Plastic Limit…………………………………………………..15 (max)
Maximum Expansive Potential (%)………………………..1.5*
*Measured on a sample compacted to approximately 9 5 percent of the ASTM D698 maximum dry density at
optimum water content. The sample is confined under a 200 psf surcharge and submerged.
4.2.3 Compaction Requirements
Engineered fill should be placed and compacted in horizontal lifts, using equipment and
procedures that will produce recommended moisture contents and densities throughout the lift.
Item Description
Fill Lift Thickness 8 to 12-inches or less in loose thickness
Compaction Requirements 98% of the material’s standard Proctor maximum dry
density (ASTM D698)
Moisture Content Non-cohesive Soil (sand) -3 to +3 % of the optimum moisture content
1. We recommend engineered fill be tested for moisture content and compaction during placement.
Should the results of the in-place density tests indicate the specified moisture or compaction limits
have not been met, the area represented by the test should be reworked an d retested as required
until the specified moisture and compaction requirements are achieved.
2. Moisture levels should be maintained low enough to allow for satisfactory compaction to be
achieved without the fill material pumping when proofrolled.
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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Item Description
3. Moisture conditioned clay materials should not be allowed to dry out. A loss of moisture within
these materials could result in an increase in the materials expansive potential. Subsequent
wetting of these materials could result in undesirable movement.
4.2.4 Grading and Drainage
All grades must be adjusted to provide positive drainage away from the structures during
construction and maintained throughout the life of the proposed project. Infiltration of water into
utility or foundation excavations must be prevented during construction. Water permitted to pond
near or adjacent to the perimeter of the structures (either during or post-construction) can result in
significantly higher soil movements than those discussed in this report. As a result, any
estimations of potential movement described in this report cannot be relied upon if positive
drainage is not obtained and maintained, and water is allowed to infiltrate the fill and/or subgrade.
Exposed ground should be sloped at a minimum of 10 percent grade for at least 5 feet beyond the
perimeter of the foundations for structures.
4.2.5 Construction Considerations
Although the exposed subgrade is anticipated to be relatively stable upon initial exposure, unstable
subgrade conditions could develop during general construction operations, particularly if the soils
are wetted and/or subjected to repetitive construction traffic. Should unstable subgrade conditions
develop, stabilization measures will need to be employed. Options for subgrade stabilization can
include removal of unsuitable material and replacement with approved fill material. An alternative
can include the use of TX-140 Tensar geogrid overlain by CDOT Class 5 or 6 aggregate base
course. The depth of aggregate base course will depend on the severity of unstable soils.
Upon completion of filling and grading, care should be taken to maintain the subgrade moisture
content prior to construction of foundations and floor slabs. Construction traffic over the
completed subgrade should be avoided to the extent practical. The site should also be graded
to prevent ponding of surface water on the prepared subgrades or in excavations. If the
subgrade should become frozen, desiccated, saturated, or disturbed, the affected material
should be removed or these materials should be scarified, moisture conditioned, and
recompacted prior to foundation or floor slab construction.
As a minimum, all temporary excavations should be sloped or braced as required by
Occupational Health and Safety Administration (OSHA) regulations to provide stability and safe
working conditions. Temporary excavations will probably be required during grading operations.
The grading contractor, by his contract, is usually responsible for designing and constructing
stable, temporary excavations and should shore, slope or bench the sides of the excavations as
required, to maintain stability of both the excavation sides and bottom. All excavations should
comply with applicable local, state and federal safety regulations, including the current OSHA
Excavation and Trench Safety Standards.
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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4.3 Foundation Recommendations
4.3.1 Monopole Foundation Design Recommendations
We anticipate the proposed monopole will be supported by a drilled pier foundation system. If
movement of the equipment shelter must be minimized, the shelter could also be constructed on
a drilled pier foundation system. For this project, we recommend the following:
Description Drilled Piers
Minimum length of embedment from existing ground surface 15 feet
Pier concrete slump (uncased piers) 5 to 7 inches
Pier concrete slump (cased piers) 7 to 9 inches
Approximate total movement 1 ¾ inch
1. The foundation movement will depend upon the variations within the subsurface soil profile, the
structural loading conditions, the quality of the earthwork operations, and maintaining uniform soil
water content throughout the life of the structure. The estimated movements are based on
maintaining uniform soil water content during the life of the structure. Additional foundation
movements could occur if water from any source infiltrates the foundation soils; therefore, proper
drainage and irrigation practices should be incorpora ted into the design and operation of the facility.
Failure to maintain soil water content and positive drainage will nullify the movement estimates
provided above.
A summary of the drilled pier foundation design recommendations is shown on the following
table. Maximum end bearing pressures given in the table are based on the cross-sectional area
of the tip of the drilled shaft. Skin friction (Sd) should be applied to the surface area of the drilled
shaft for that given length interval below a depth of 36 inches. The combination of skin friction
and end bearing pressure can be used to determine the vertical compression capacity. The
skin friction value should be used to determine the uplift capacity of the pier.
For lateral load and overturning design, we have included beam on elastic foundation spring
constants, lateral equivalent earth pressures, and more commonly used LPILE parameters. For
calculation of lateral deflection using the beam on elastic foundation method, a coefficient of
subgrade reaction listed on the table may be used for the analysis. Lateral load design
parameters are valid for maximum soil strain of 1 percent for the native soils acting over a
distance of one shaft diameter. The passive pressure, coefficient of horizontal subgrade
reaction, and LPILE parameters are ultimate values; therefore, appropriate factors of safety
should be applied in the pier design.
Description Sand Fill Materials Native Sand Soils
Bearing Depth (ft) 3 to 10 feet 13 to 21 feet
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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Description Sand Fill Materials Native Sand Soils
Allowable Vertical Parameters
Bearing, psf
Skin Friction, Sd (psf)
1,500
30
6,500
160
Ultimate Lateral Parameters
Beam on Elastic Foundation:
Passive, EFP (psf/ft)
Coef. of Hori. Sub. Reaction, ki, (tcf)
340
4
420
14
Soil Code 3 3
Unit Weight, (pci) 0.061 0.067
Su (psi) 0 0
Angle of internal Friction, (degrees)32 35
Horizontal Modulus of Subgrade Reaction:
Static, k (pci)
Cyclic, k (pci)
90
32
225
34
Strain at 50% of Maximum Stress, 50 0 0
We recommend neglecting skin friction and lateral resistance for the upper 36 inches of drilled
piers because of the effects of frost.
Piers should be considered to work in group action if the horizontal spacing is less than 6 pier
diameters. A minimum practical horizontal spacing between piers of at least 3 diameters should
be maintained, and adjacent piers should bear at the same elevation. The capacity of individual
piers must be reduced when considering the effects of group action. Capacity reduction is a
function of pier spacing and the number of piers within a group. If group action analyses are
necessary, capacity reduction factors can be provided for the analyses.
4.3.2 Monopole Foundation Construction Considerations
Drilling to depths less than about 20 feet should be possible with conventional single flight
power augers. However, drilling to depths greater than about 20 feet may require specialized
drilling equipment. Pier concrete should be placed soon after completion of drilling and
cleaning. Due to potential sloughing and raveling, foundation concrete quantities may exceed
calculated geometric volumes.
We anticipate groundwater will be encountered during installation of the drilled piers. Therefore,
a tremie or casing should be used for concrete placement. 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 a
relatively high fluidity when placed in cased pier holes or through a tremie.
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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Free-fall concrete placement in piers will only be acceptable if provisions are taken to avoid
striking the concrete on the sides of the hole or reinforcing steel and there is no water at the
bottom of the pier excavation. The use of a bottom-dump hopper, or an elephant's trunk
discharging near the bottom of the hole where concrete segregation will be minimized, is
recommended.
Shaft bearing surfaces must be free of loose materials prior to concrete placement. A
representative of the geotechnical engineer should observe the bearing surface and shaft
configuration.
4.3.3 Equipment Shelter Design Recommendations
A concrete slab–on-grade foundation system is considered suitable for support of the proposed
equipment support building, provided the owner is willing to accept some risk of movement . If
the owner is not willing to accept the risk of movement, the proposed equipment shelter should
be supported by a drilled pier foundation system. For protection against frost heave, all exterior
foundations should be constructed at a depth of 36 inches below the ground surface.
The proposed equipment building can also be supported by a shallow, spread footing foundation,
provided the owner can tolerate some movement. Based upon the laboratory testing completed,
we estimate potential foundation movement on the order of about 1 inch or more is possible for
the in-place fill.
To provide more uniform support conditions and to improve performance, consideration could
be given to partial modification of the existing fill. Partial modification of existing fill would
consist of removal of 3 feet of fill below the equipment shelter, moisture-conditioning, and
replacement of the fill as new, properly compacted engineered fill. If movement must be
minimized the equipment shelter could be constructed on a drilled pier foundation.
Design recommendations for shallow foundations for the proposed equipment shelter are
presented in the following paragraphs.
Description Value
Net allowable bearing pressure 1 2,000 psf
Minimum amount of compacted fill
beneath bearing surface 36 inches
Minimum embedment below
finished grade for frost protection 36 inches
Approximate total movement 2 1 to 2 inches or more
Estimated differential movement 3 ½ to ¾ of total
1. The recommended net allowable bearing pressure is the pressure in excess of the
minimum surrounding overburden pressure at the footing base elevation. The design
bearing pressure applies to design dead loads plus design live load conditions.
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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Description Value
2. The foundation movement will depend upon the variations within the subsurface soil
profile, the structural loading conditions, the embedment depth of the footings, t he
thickness of compacted fill, the quality of the earthwork operations, and maintaining
uniform soil water content throughout the life of the structure. The estimated movements
are based on maintaining uniform soil water content during the life of the structure.
Additional foundation movements could occur if water from any source infiltrates the
foundation soils; therefore, proper drainage and irrigation practices should be
incorporated into the design and operation of the facility. Failure to maintain soil water
content and positive drainage will nullify the movement estimates provided above.
3. If this magnitude of movement cannot be tolerated, we recommend that the equipment
shelter also be supported on drilled shaft foundations with a minimum length of 15 feet.
The same drilled shaft recommendations presented for the monopole should be utilized in
the design of the equipment shelter.
4.3.4 Equipment Shelter Construction Considerations
Fill (if any) should be placed in lifts of 8 inches or less in loose thickness and compacted to at
least 98 percent of the material's maximum dry density (ASTM D698). Compactive effort should
be in accordance with recommendations provided in the Earthwork section of this report.
Concrete should be placed soon after excavating to reduce bearing soil disturbance. Should
the soils at bearing level become excessively dry, disturbed or saturated, or frozen, the affected
soil should be removed prior to placing concrete.
It is recommended that a construction testing laboratory be retained to observe and test the soil
foundation bearing materials.
4.4 Seismic Considerations
Code Used Site Classification
2009 International Building Code (IBC) 1 D 2
1. In general accordance with the 2009 International Building Code, Table 1613.5.2.
2. The 2009 International Building Code (IBC) requires a site soil profile determination extending a
depth of 100 feet for seismic site classification. The current scope requested does not include the
required 100 foot soil profile determination. The boring for the monopole extended to a maximum
depth of about 21 feet and this seismic site class definition considers that similar soil conditions exist
below the maximum depth of the subsurface exploration. Additional exploration to deeper depths
could be performed to confirm the conditions below the current depth of exploration. Alternatively, a
geophysical exploration could be utilized in order to attempt to justify a higher seismic site class.
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
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4.5 Corrosion Protection
The following table lists the results of laboratory soluble sulfate, pH and soil resistivity testing.
The soluble sulfate concentration, pH and electrical resistivity values may be used to estimate
potential corrosive characteristics of the on-site soils with respect to contact with the various
underground materials which will be used for project construction.
Boring No. Sample Depth
(feet)
Soluble Sulfate1
(mg/l) pH
Electrical
Resistivity
Ohm-cm
1 0 - 5 1 8.5 4600
1. Results of soluble sulfate testing indicate that a sample of the on-site soils tested possess
negligible sulfate concentrations when classified in accordance with Table 4.3.1 of the ACI
Design Manual. The results of the testing indicate ASTM Type I Portland Cement is suitable for
project concrete on and below grade. However, if there is no (or minimal) cost differential, use
of ASTM Type II Portland Cement is recommended for additional sulfate resistance of
construction concrete. Concrete should be designed in accordance with the pro visions of the
ACI Design Manual, Section 318, Chapter 4.
5.0 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 design and specifications. Terracon also should be retained to provide observation and
testing services during grading, excavation, foundation construction and other earth-related
construction phases of the project.
The analysis and recommendations presented in this report are based upon the data obtained
from the boring performed at the indicated locations and from other information discussed in this
report. This report does not reflect variations that may occur across the site, or due to the
modifying effects of construction or 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 expressed or implied, are intended or made. Site
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
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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.
APPENDIX A
FIELD EXPLORATION
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
Responsive ■ Resourceful ■ Reliable Exhibit A-1
Field Exploration Description
One test boring was advanced within the general vicinity of the monopole and equipment shelter to
a depth of about 21 feet below existing site grade at the approximate location shown on the Boring
Location Plan, Exhibit A-2. The boring was advanced with an ATV-mounted drilling rig, utilizing 6-
inch diameter solid-stem auger.
The boring location was located in the field by measuring from existing site features. The
accuracy of the boring location should only be assumed to the level implied by the methods used.
During the drilling operations, a lithologic log of the boring was recorded by the field engineer.
Relatively undisturbed samples were obtained at selected intervals utilizing a 3-inch outside
diameter ring barrel sampler (RS) and a 2-1/2 inch diameter split-spoon sampler (SS).
Penetration resistance values were recorded in a manner similar to the standard penetration
test (SPT). This test consists of driving the sampler into the ground with a 140-pound hammer
free-falling through a distance of 30 inches. The number of blows required to advance the ring-
barrel sampler 12 inches or the interval indicated, is recorded and can be correlated to the
standard penetration resistance value (N-value). The blow count values are indicated on the
boring logs at the respective sample depths, ring barrel sample blow counts are not considered
N-values.
An automatic SPT hammer was used to advance the sampler in the boring performed on this
site. A greater efficiency is typically achieved with the automatic hammer compared to the
conventional safety hammer operated with a cathead and rope. Published correlations between
the barrel blow counts, SPT values, and soil properties are based on the lower efficiency
cathead and rope method. This higher efficiency affects the standard penetration resistance
blow count value by increasing the penetration per hammer blow over what would be obtained
using the cathead and rope method. The effect of the automatic hammer's efficiency has been
considered in the interpretation and analysis of the subsurface information for this report.
Groundwater measurements were obtained in the boring at the time of site exploration. The boring
was backfilled with auger cuttings prior to leaving the site. Some settlement of the backfill should
be anticipated.
BORING LOCATION DIAGRAM
AT&T Vail – Site 810106
1309 Elkhorn Drive
Vail, Colorado
A-2
10625 W. I-70 Frontage Rd. N. Wheat Ridge, Colorado 80033
PH. (303) 423-3300 FAX. (303) 423-3353
25125082
09/05/2012
SBM
CMD
SBM
SBM
1” = 20’
Project Manager:
Drawn by:
Checked by:
Approved by:
Project No.
Scale:
File Name:
Date:
Exhibit
25125082
.
DIAGRAM IS FOR GENERAL LOCATION
ONLY, AND IS NOT INTENDED FOR
CONSTRUCTION PURPOSES
0’ 10’ 20’
GRAPHIC SCALE
1 APPROXIMATE BORING LOCATION
LEGEND
1 Approximate Boring Location
P1 Approximate Percolation Test Location
1 Approximate Boring Location
(Terracon Project No. 25055250)
P1
APPROXIMATE PERCOLATION TEST LOCATION 0’ 30’ 60’
1
0.3
6.0
8.0
10.0
21.0
ASPHALT, (4 inches)
FILL - FINE TO COARSE SAND, with clay, gravel and cobbles, dark
brown, medium dense
FILL - SANDY LEAN CLAY, trace gravel, brown, stiff
FILL - CLAYEY SAND, fine to coarse grained, brown, loose
FINE TO COARSE SAND (SW-SC), with clay, gravel, cobbles and
boulders, brown, medium dense
Auger Refusal at 21 Feet
60
18
18
60
12
12
18
18
51
43
10
12
21
15
3
2
12-9-5
34-15-10
7-7
4-5
6-22-27
18-12-20
103
115
36-23-13
25-17-8
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.
LOCATION
GR
A
P
H
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O
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DEPTH
See Exhibit A-2
TH
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2
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1
2
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8
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9
/
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1
2
1309 Elkhorn Drive
Vail, Colorado
SITE:
Water not encountered during drilling
WATER LEVEL OBSERVATIONS
PROJECT: AT&T Vail - Site 810106
Page 1 of 1
Advancement Method:
6-inch diameter solid-stem flight auger
Abandonment Method:
Borings backfilled with soil cuttings upon completion.
10625 W I-70 Frontage Road N., Ste. 3
Wheat Ridge, Colorado
Notes:
Project No.: 25125082
Drill Rig: CME ATV
Boring Started: 8/28/2012
BORING LOG NO. 1
Atecs, LLC.
See Appendix C for explanation of symbols and
abbreviations.
CLIENT:
See Appendix B for description of laboratory
procedures and additional data, (if any).
See Exhibit A-1 for description of field
procedures
Exhibit
Driller:
A-3
Boring Completed: 8/28/2012
RE
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(
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PE
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WA
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CO
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(
%
)
FI
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SA
M
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WA
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OB
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DE
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H
(
f
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5
10
15
20
25
30
DR
Y
U
N
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WE
I
G
H
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(
p
c
f
)
ATTERBERG
LIMITS
LL-PL-PI
APPENDIX B
LABORATORY TESTING
Geotechnical Engineering Report
AT&T Vail – Site 810106 ■ Vail, Colorado
September 6, 2012 ■ Terracon Project No. 25125082
Responsive ■ Resourceful ■ Reliable Exhibit B-1
Laboratory Testing
Samples retrieved during the field exploration were returned to the laboratory for observation by
the project geotechnical engineer. An applicable laboratory testing program was formulated to
determine engineering properties of the subsurface materials. The field descriptions were
confirmed or modified as necessary, and were classified in general accordance with the Unified
Soil Classification System described in Appendix C.
Laboratory test results are presented on the Boring Log and in Appendix B, and were used for
the geotechnical engineering analyses, and the development of foundation and earthwork
recommendations. Laboratory tests were performed in general accordance with the applicable
Terracon test standards.
Selected soil and bedrock samples were tested for the following engineering properties:
Water content
Dry density
pH
Atterberg
Grain size distribution
Swell/consolidation
Water soluble sulfate content
Electrical soil resistivity
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
6 16 20 30 40 501.5 2006810
50.9
42.8
1.5
4.5
14
LL PL PI
%Clay%Silt
413/4 1/2 60
fine
HYDROMETERU.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
23
17
13
8
D100
Cc Cu
SILT OR CLAY
4
%Sand%Gravel
ASTM D422
D30 D10
1
1
SANDY LEAN CLAY(CL)
CLAYEY SAND(SC)
36
25
0.163
0.278
9.5
12.5
1
1
7.0
9.0
GRAIN SIZE IN MILLIMETERS
PE
R
C
E
N
T
F
I
N
E
R
B
Y
W
E
I
G
H
T
coarse fine
GRAIN SIZE DISTRIBUTION
3/8 3 100 14032
COBBLES GRAVEL SAND
USCS Classification
47.7
52.7
D60
coarse medium
7.0
9.0
Boring ID Depth
Boring ID Depth
EXHIBIT: B-2
10625 W I-70 Frontage Road N., Ste. 3
Wheat Ridge, Colorado
PROJECT NUMBER: 25125082PROJECT: AT&T Vail - Site 810106
SITE: 1309 Elkhorn Drive
Vail, Colorado CLIENT: Atecs, LLC.
LA
B
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-
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2
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Surcharge
(ksf)Swell (%)1-1/2"#4 #10 #40 #200 LL PI
1 0 - 5 SP-SC 10 8.5 4600 1 5
1 4 SP-SC 12 5
1 7 CL 103 21 100 99 94 74 51 36 13
1 9 SC 115 15 100 95 89 67 43 25 8
1 14 SW-SC 3 5
1 19 SW-SC 2 5
Notes:
Initial Dry Density, Initial Water Content, and Swell/Consolidation values obtained from undisturbed samples unless otherwise noted
* = Partially disturbed sample
- = Compression/settlement
NV = no value
NP = non-plastic
REMARKS
1 Remolded Compacted density (approximately 95% of ASTM D698 maximum density near optimum)
2 Remolded Compacted density (approximately 95% of ASTM D1557 maximum density near optimum)
3 Submerged to approximate saturation Exhibit B-34Dry density and/or moisture content determined from one ring of a multi-ring sample
5 Visual Classification
6 Minus #200 Only
Remarks
SUMMARY OF LABORATORY TEST RESULTS
AT&T Vail - Site 810106
Terracon Project No. 25125082
Boring
No.
Depth
(ft.)
Water
Soluble
Sulfates
(mg/l)
Swell/ConsolidationUSCS Soil
Classification
Initial Dry
Density
(pcf)
Initial
Water
Content
(%)
pH
Electrical
Resistivity
(Ohm/cm)
Atterberg
Limits
Particle Size Distribution, Percent
Passing by Weight
APPENDIX C
SUPPORTING DOCUMENTS
< 20
Soil classification is based on the Unified Soil 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.
Plasticity Index
0
1 - 10
11 - 30
> 30
RELATIVE PROPORTIONS OF FINES
Descriptive Term(s)
of other constituents
Percent of
Dry Weight
< 5
5 - 12
> 12
Trace
With
Modifier
Water Level After
a Specified Period of Time
GRAIN SIZE TERMINOLOGYRELATIVE PROPORTIONS OF SAND AND GRAVEL
Trace
With
Modifier
Exhibit C-1
WA
T
E
R
L
E
V
E
L
Auger
Shelby Tube
Loose
Medium Dense
Very Dense
10 - 29
4 - 9
19 - 58
500 to 1,000
less than 500
5 - 7 5 - 9
3 - 4
< 3
Ring
Sampler
Blows/Ft.
< 30
30 - 49
> 119
PLASTICITY DESCRIPTION
Term
< 15
15 - 29
> 30
Descriptive Term(s)
of other constituents
Water Initially
Encountered
Water Level After a
Specified Period of Time
Major Component
of SamplePercent of
Dry Weight
LOCATION AND ELEVATION NOTES
RELATIVE DENSITY OF COARSE-GRAINED
SOILS
Descriptive
Term
(Density)
Ring
Sampler
Blows/Ft.
Dense
> 50
30 - 50
_4,000 to 8,000
> 30
15 - 30
8 - 14
> 42
19 - 42
(50% or more passing the No. 200 sieve.)
Consistency determined by laboratory shear strength testing,
field visual-manual procedures or standard penetration
resistance
SA
M
P
L
I
N
G
FI
E
L
D
T
E
S
T
S
(HP)
(T)
(b/f)
(PID)
(OVA)
DESCRIPTION OF SYMBOLS AND ABBREVIATIONS
EXPLANATION OF BORING LOG INFORMATION
Non-plastic
Low
Medium
High
Boulders
Cobbles
Gravel
Sand
Silt or Clay
Hand Penetrometer
Torvane
Standard Penetration
Test (blows per foot)
Photo-Ionization Detector
Organic Vapor Analyzer
Water levels indicated on the soil boring
logs are the levels measured in the
borehole at the times indicated.
Groundwater level variations will occur
over time. In low permeability soils,
accurate determination of groundwater
levels is not possible with short term
water level observations.
DESCRIPTIVE SOIL CLASSIFICATION
Unless otherwise noted, Latitude and Longitude are approximately determined using a hand-held GPS device. The accuracy
of such devices is variable. Surface elevation data annotated with +/- indicates that no actual topographical survey was
conducted to confirm the surface elevation. Instead, the surface elevation was approximately determined from topographic
maps of the area.
7 - 18
59 - 98
> 99
Descriptive
Term
(Consistency)
2,000 to 4,000
1,000 to 2,000
10 - 18
CONSISTENCY OF FINE-GRAINED SOILS
Ring Sampler
Grab Sample
Split Spoon
Macro Core
Rock Core
No Recovery
Particle Size
Over 12 in. (300 mm)
12 in. to 3 in. (300mm to 75mm)
3 in. to #4 sieve (75mm to 4.75 mm)
#4 to #200 sieve (4.75mm to 0.075mm
Passing #200 sieve (0.075mm)
ST
R
E
N
G
T
H
T
E
R
M
S
(More than 50% retained on No. 200 sieve.)
Density determined by
Standard Penetration Resistance
Includes gravels, sands and silts.
Standard
Penetration or
N-Value
Blows/Ft.
0 - 6Very Loose 0 - 3 Very Soft
Soft
Medium-Stiff
Stiff
Very Stiff
Hard
Unconfined
Compressive
Strength,
Qu, psf
2 - 4
0 - 1
Standard
Penetration or
N-Value
Blows/Ft.
Ring
Sampler
Blows/Ft.
50 - 89
90 - 119
20 - 29
50 - 79
>79
Descriptive
Term
(Consistency)
Standard
Penetration or
N-Value
Blows/Ft.
BEDROCK
Weathered
Firm
Medium Hard
Hard
Very Hard
30 - 49
> 8,000
Exhibit C-2
UNIFIED SOIL CLASSIFICATION SYSTEM
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests A
Soil Classification
Group
Symbol Group Name B
Coarse Grained Soils:
More than 50% retained
on No. 200 sieve
Gravels:
More than 50% of
coarse fraction retained
on No. 4 sieve
Clean Gravels:
Less than 5% fines C
Cu 4 and 1 Cc 3 E GW Well-graded gravel F
Cu 4 and/or 1 Cc 3 E GP Poorly graded gravel F
Gravels with Fines:
More than 12% fines C
Fines classify as ML or MH GM Silty gravel F,G,H
Fines classify as CL or CH GC Clayey gravel F,G,H
Sands:
50% or more of coarse
fraction passes No. 4
sieve
Clean Sands:
Less than 5% fines D
Cu 6 and 1 Cc 3 E SW Well-graded sand I
Cu 6 and/or 1 Cc 3 E SP Poorly graded sand I
Sands with Fines:
More than 12% fines D
Fines classify as ML or MH SM Silty sand G,H,I
Fines classify as CL or CH SC Clayey sand G,H,I
Fine-Grained Soils:
50% or more passes the
No. 200 sieve
Silts and Clays:
Liquid limit less than 50
Inorganic: PI 7 and plots on or above “A” line J CL Lean clay K,L,M
PI 4 or plots below “A” line J ML Silt K,L,M
Organic: Liquid limit - oven dried 0.75 OL Organic clay K,L,M,N
Liquid limit - not dried Organic silt K,L,M,O
Silts and Clays:
Liquid limit 50 or more
Inorganic: PI plots on or above “A” line CH Fat clay K,L,M
PI plots below “A” line MH Elastic Silt K,L,M
Organic: Liquid limit - oven dried 0.75 OH Organic clay K,L,M,P
Liquid limit - not dried Organic silt K,L,M,Q
Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat
A Based on the material passing the 3-inch (75-mm) sieve
B If field sample contained cobbles or boulders, or both, add “with cobbles
or boulders, or both” to group name.
C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded
gravel with silt, GW -GC well-graded gravel with clay, GP-GM poorly
graded gravel with silt, GP-GC poorly graded gravel with clay.
D Sands with 5 to 12% fines require dual symbols: SW -SM well-graded
sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded
sand with silt, SP-SC poorly graded sand with clay
E Cu = D60/D10 Cc =
6010
2
30
DxD
)(D
F If soil contains 15% sand, add “with sand” to group name.
G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.
H If fines are organic, add “with organic fines” to group name.
I If soil contains 15% gravel, add “with gravel” to group name.
J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.
K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,”
whichever is predominant.
L If soil contains 30% plus No. 200 predominantly sand, add “sandy” to
group name.
M If soil contains 30% plus No. 200, predominantly gravel, add
“gravelly” to group name.
N PI 4 and plots on or above “A” line.
O PI 4 or plots below “A” line.
P PI plots on or above “A” line.
Q PI plots below “A” line.