HomeMy WebLinkAboutB12-0059_Geotechnical recommendations_121411_11-6024Subsurface Exploration Program and
Geotechnical Recommendations
Proposed Concert Hall Plaza Addition
Vail, Colorado
Prepared For:
Town of Vail
75 S. Frontage Road
Vail, Colorado 81657
Attention: Mr. Tom Kassmel
Job Number: 11 -6024
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ENGINEERING CONSLJLTRNTS INC.
December 14, 2011
379 Indian Road, Grand Junction, CO 81501 Phone (970) 242 -4300 Fax (970) 242 -4301 www.groundeng.com
Office Locations: Englewood Commerce City . Loveland Granby . Gypsum Grand Junction . Casper
Proposed Concert Hall Plaza Addition
610 W. Lionshead Circle
Vail, Colorado
TABLE OF CONTENTS
Page
Purpose and Scope of Study ...................................................... ...............................
1
ProposedConstruction ............................................................... ...............................
1
SiteConditions ........................................................................... ...............................
1
Regional and Project Site Geology .............................................. ...............................
2
SeismicClassification ................................................................. ...............................
2
Subsurface Exploration .............................................................. ...............................
3
LaboratoryTesting ..................................................................... ...............................
3
Subsurface Conditions ............................................................... ...............................
4
Geotechnical Considerations For Design ........................................ ..............................5
FoundationSystems ........................................................................ ..............................5
FloorSystems ................................................................................. ..............................8
ExteriorFlatwork ...................................................................... ...............................
10
Water Soluble Sulfates ............................................................... ...............................
13
SoilCorrosivity ........................................................................... ...............................
14
ProjectEarthwork ...................................................................... ...............................
16
Excavation Considerations ....................................................... ...............................
20
BusTransit Plaza ........................................................................... .............................20
SurfaceDrainage ..................................................................... ...............................
25
FoundationWalls ........................................................................... .............................27
Closure...................................................................................... ...............................
28
Locations of Test Holes .................................................... ...............................
Figure 1
Logof Test Hole .............................................................. ...............................
Figure 2
Legend and Notes ............................................................ ...............................
Figure 3
Consolidation Test Results ............................................... ...............................
Figure 4
Proposed Concert Hall Plaza Addition
610 W. Lionshead Circle
Vail, Colorado
Summary of Laboratory Test Results ............................... ............................... Table 1
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsurface exploration program performed by
GROUND Engineering Consultants, Inc. (GROUND) to develop geotechnical
recommendations for the proposed concert hall plaza addition located northwest of the
existing building located at 610 W. Lionshead Circle, Vail, Colorado. Our study was
conducted in general accordance with GROUND's Proposal No. 1110 -1592, dated
November 3, 2011.
A field exploration program was conducted to obtain information on subsurface
conditions at the site. Material samples obtained during the subsurface exploration were
tested in our laboratory to provide data on the classification and engineering
characteristics of the on -site soils. The results of the field exploration and laboratory
testing are presented herein.
This report has been prepared to summarize the data obtained and to present our
conclusions and recommendations based on the proposed construction and the
subsurface conditions encountered. Design parameters and a discussion of
geotechnical engineering considerations related to construction are included herein.
PROPOSED CONSTRUCTION
We understand that proposed construction is preliminary, but likely will consist of a one -
story addition at the northwest corner of the existing building for addition of a
mechanical /boiler room. We understand a below grade level may be included in
construction. Loads are anticipated to be light to moderate, typical of this type of
construction. If the proposed construction differs significantly from that described above,
GROUND should be notified to re- evaluate the recommendations contained herein.
SITE CONDITIONS
The existing concert hall is a single -story structure with a below grade basement level.
The building is located just north and east from the bus station `transit plaza' east of
West Lionshead Circle. (See Figure 1.) The surrounding area has been developed for
commercial use with restaurants and shopping areas with areas of landscaped grass,
bushes, and trees. The general topography at the site is gently to moderately sloping
with an overall slope of approximately 10 percent descending towards the southwest.
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
REGIONAL, PROJECT SITE GEOLOGY AND POTENTIAL HAZARDS
The project area is located near the northern tip of the north- trending Sawatch Range
anticlinal uplift, a geologic structure that developed during the Laramide orogeny (about
40 to 80 million years ago), and east of the Colorado evaporate region and Burns
Syncline. Surficial deposits at the project site are mapped as outwash sands and
gravels (Qg) associated with the Pinedale Glaciation which overlie the Pennsylvanian
Age Minturn Formation.
The closest geologically young faults exhibiting movement in the last 15,000 years that
are considered capable of generating large earthquakes are located in the northern
section of the Williams Fork Mountains fault zone, about 20 miles north of the project
site.
Although rockfall, landslide, and avalanche hazards do occur in the area, In our opinion,
we consider the possibility of such a geologic hazard affecting the project site to be low
compared to areas of closer proximity to surrounding hillsides.
SEISMIC CLASSIFICATION
Utilizing the USGS's Earthquake Ground Motion Tool v.5.1.0 and site approximate
latitude /longitude coordinates [of 39.6438 and — 106.3903 (obtained from Google Earth)
respectively], the project site is indicated to be subject to an SDs value of 0.285g and an
SD1 value of 0.068g. Compared with other regions of the Western United States,
recorded earthquake frequency in the project vicinity is relatively low.
In the absence of actual shear wave velocity testing /analysis or deep drilling, GROUND
estimates that a Seismic Site Class D according to the 2006/2009 IBC classification
(Table 1613.5.2) is applicable to the site. In the event that the owner desires to utilize
Site Class C for design, according to the 2006/2009 IBC, actual downhole seismic shear
wave velocity testing and /or exploration to subsurface depths of at least 100 feet, should
be performed. Based on available data, we consider the likelihood of realizing a Site
Class C to be low.
SUBSURFACE EXPLORATION
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 4 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
The subsurface exploration for the project site was conducted on November 11, 2011.
One test hole was located in an area northwest of the existing building within the
proposed footprint of the proposed construction. A second test hole was located in the
bus turnaround area southwest of the Concert Hall Plaza. The test hole depths were
18% and 6 feet below existing surface grade for the concert hall plaza addition and bus
turnaround area, respectively. Test holes were advanced using a conventional, track -
mounted, drilling rig to evaluate the subsurface conditions, as well as to retrieve soil
samples for laboratory testing and analysis.
A GROUND engineer directed the subsurface exploration, logged the test holes in the
field, and prepared the soil samples for transport to our laboratory.
Samples of the subsurface materials were retrieved with a 2 -inch I.D. "California" -type
liner sampler and a 1% -inch I.D. Standard Penetration Test ( "split spoon ") sampler. The
samplers were driven into the substrata with blows from a 140 -pound hammer falling 30
inches. This procedure is similar to the Standard Penetration Test described by ASTM
Method D1586. Penetration resistance values, when properly evaluated, indicate the
relative density or consistency of soils. Depths at which the samples were obtained and
associated penetration resistance values are shown on the test hole logs.
The approximate locations of the test holes are shown in Figure 1. Logs of the
exploratory test holes are presented in Figure 2. Explanatory notes and a legend are
provided in Figure 3. To locate the test holes, GROUND utilized the site plan provided
by The Town of Vail indicating existing features.
LABORATORY TESTING
Samples retrieved from our test holes were examined and visually classified in the
laboratory by the project engineer. Laboratory testing of soil samples obtained from the
subject site included standard property tests, such as natural moisture contents, dry unit
weights, grain size analyses, and liquid and plastic limits. Swell- consolidation, water -
soluble sulfate and corrosivity tests were performed on selected samples of the soils as
well. Laboratory tests were performed in general accordance with applicable ASTM and
AASHTO protocols. Results of the laboratory testing program are summarized on
Tables 1.
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 5 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
SUBSURFACE CONDITIONS
The subsurface conditions encountered in the addition test hole generally consisted of
about 8 feet of undocumented fill materials over sands and gravels. Dense sandy
gravels and cobbles were encountered below 16 feet and practical drilling refusal
occurred at a depth of 181/2 feet below surface grade. The pavement test hole
encountered approximately 31/2 feet of fill below 61/4 inches of asphalt over 10 inches of
base course. Native soils below 31/2 feet consisted of silty sands with gravels.
Groundwater was not encountered in the test holes at the time of drilling and the test
hole caved at 5 feet.
Fill The fill soils encountered consisted of fine to coarse sands with gravel, clay, silt and
scattered cobbles and possible boulders. Fill material was loose to very dense, moist,
and dark brown in color.
Sand and Gravels with Cobbles and possible boulders. The natural soils encountered
were stratified layers of clean sand and sandy gravels with scattered cobbles. Very
dense cobbles and possible boulders were encountered below 16 feet. Soils generally
consisted of medium to coarse sands, angular to sub - rounded gravels, medium dense,
moist, and light brown to brown in color.
It should be noted that it is not possible to characterize coarse gravel -, cobble- and
boulder -sized materials in small diameter test holes. Therefore, those relying on this
report should anticipate that coarser materials than recognized herein may be present in
the soils at this site.
Swell- Consolidation Testing suggested a potential for consolidation in the sands and
gravels when wetted under various surcharge loads.
Tests performed on samples of sandy silty gravel at Test Hole 1 indicated a potential for
consolidation up to 3.7 percent. A sample of silty sand at Test Hole 2 indicated a
potential for consolidation up to 4.0 percent.
Groundwater was not encountered in the test holes at the time of drilling to the depths
explored, however, fluctuations in ground water levels may occur and the water table
may be significantly higher during spring and summer seasons.
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 6 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
GEOTECHNICAL CONSIDERATIONS FOR DESIGN
The fill and native sandy gravels and sands encountered at shallow to moderate depths
across much of the site to depths of 16 feet or more have the potential for vertical
movement upon wetting. GROUND recommends a deep foundation system extending
into dense gravels would provide the least risk of post construction movement. Micro -
piles may be the most cost - efficient deep foundation system for the area. It should be
noted that somewhat greater strains commonly are required for this type of foundation
system to mobilize their strength relative to drilled piers or driven H- piles. Therefore,
apparent settlements upon imposition of structural loads may be up to 1 inch. A micro -
pile system is designed and installed by a specialty supplier / contractor and we
anticipate that the subsurface information provided in this report is sufficient for designs
of a micro -pile system to be developed. Subsurface sands and gravels became denser
at 16 feet below surface grade and drilling refusal was encountered at 18'/2 feet. It may
be necessary to advance micro -piles 10 feet below this dense layer, however, actual
penetration depths should be developed by the micropile contractor.
As a higher risk alternative, the addition can be supported on spread footings provided
that surface moisture is carefully controlled and a section of properly compacted soil is
constructed beneath the addition. Therefore, geotechnical parameters for a shallow
foundation are provided below. Parameters for a non - proprietary deep foundation
system can be provided upon request.
Supporting a shallow foundation system and a slab -on -grade floor directly on the local
soils, could experience likely total and differential vertical movements on the order of 5
or more inches. If constructed on a properly prepared fill section as described below,
likely building foundation movements of approximately 1 to 2 inches with differential
movements of 1 inch over a span of 30 feet are estimated.
FOUNDATION SYSTEMS
The design and construction criteria presented below may be observed for a spread
footing foundation system. The construction details can be considered when preparing
project documents. The precautions and recommendations provided below will not
prevent movement of the footings if the underlying materials are allowed to become wet.
However, the recommended measures will tend to make the movement more uniform,
and reduce resultant damage if such movement occurs.
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 7 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
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Vail, Colorado
1. Footings should bear on at least 4 feet of properly moisture - conditioned and
compacted fill soils. The existing soils should be excavated from beneath the
building footprint to a depth of 4 feet or more below the lowest foundation
element, thoroughly mixed, moisture conditioned and replaced as properly
compacted fill.
Excavation and replacement to the full, recommended depth should extend at
least 4 feet beyond the building perimeter.
The contractor should provide surveyed elevations of the bottoms of the
excavations beneath the building verifying that the remedial excavation was
advanced to a sufficient depth.
Recommendations for fill placement and compaction are provided in the Project
Earthwork section of this report.
The Contractor should take care to construct a fill layer of uniform composition to
reduce differential post- construction building, slab and flatwork movements. In
addition, scarification and re- compaction of the underlying 8 to 12 inches of
material at the base of the excavated section should be performed and
compacted to the density requirements specified in the Project Earthwork section
of this geotechnical report.
2. Footings bearing on at least 4 feet of properly compacted fill may be designed for
an allowable soil bearing pressure A) of 1,500 psf for a footing width up to 4
feet in minimum, lateral dimension. A geotechnical engineer should be retained
to provided bearing pressures where larger footings are used. These values may
be increased by 1/3 for transient loads such as wind or seismic loading.
Based on these recommended allowable bearing pressure, we anticipate post -
construction settlements from direct compression of the foundation soils to be on
the order of 1 inch.
3. In order to reduce differential settlements between footings or along continuous
footings, footing loads should be as uniform as possible. Differentially loaded
footings will settle differentially.
4. Connections to the structures of all types must be flexible and /or adjustable to
accommodate the potential, post- construction movements.
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 8 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
5. Spread footings should have a minimum footing lateral dimension of 16 or more
inches for linear strip footings and a minimum lateral dimension of 24 or more
inches for isolated pad or drilled footings. Actual footing dimensions, however,
should be determined by the structural engineer, based on the design loads.
6. Footings should bear at an elevation 4 or more feet below the lowest adjacent
exterior finish grades to have adequate soil cover above their bearing elevation
for frost protection.
7. Continuous foundation walls should be reinforced top and bottom to span an
unsupported length of at least 10 feet.
8. The lateral resistance of spread footings will be developed as sliding resistance
of the footing bottoms on the onsite soil. Sliding friction at the bottom of footings
may be taken as 0.40 times the vertical dead load.
9. The addition should be isolated, structurally, from the existing building. Finishes
that span the joints between building and addition should be tolerant of
differential movement and /or readily replaced.
10. Compacted fill placed against the sides of the footings should be compacted to at
least 95 percent relative compaction in accordance with the recommendations in
Project Earthwork section of this report.
11. Care should be taken when excavating the foundation to avoid disturbing the
supporting materials.
12. Footing excavation bottoms may expose organics, debris, loose, wet or
otherwise unsuitable materials which should be excavated and replaced with
properly compacted fill.
FLOOR SYSTEMS
Constructing the building floors as structural floors, supported on deep foundations in the
same manner as the building, is the most effective way of limiting post- construction floor
movements. We recommend providing the addition with structural floors to minimize
floor movements. Detailed recommendations for struc
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 9 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
Slab -on -Grade Concrete Floor We understand that conventional slab -on -grade floors
are generally acceptable in the project area. However, such a system would represent a
higher risk alternative to a structural floor.
We estimate that post- construction floor movements of approximately 2 inches are likely,
with similar differential movements over spans of about 30 feet. The criteria below may
be followed if a slab -on -grade floor is selected.
1. The floor system should bear on a section of properly compacted fill at least 8
feet in thickness.
We estimate likely post- construction movement of a slab constructed on 8 feet of
fill to be about 1 inch.
The thickness of the fill section should be taken from the bottom of the slab +
gravel layer system. If the gravel layer is not installed, the fill section should be
correspondingly thickened.
Screened rock (coarser than 3/4 -inch) may be used at the base of the fill to
facilitate drainage during times of high water table. If screened rock is used, a
layer of filter fabric should be placed on the screened rock, beneath the common
fill.
The contractor should survey the excavations beneath the building verifying that
the remedial excavations were advanced to a sufficient depth and extent.
The contractor should take care to construct a fill section of uniform depth and
composition to reduce differential post- construction addition, slab and flatwork
movements. A differential fill beneath the addition will tend to increase
differential movements.
Organics, or loose, soft or otherwise unsuitable materials exposed on the
prepared surface on which a floor slab will be cast should be excavated and
replaced with properly compacted fill.
2. Concrete slabs -on -grade should be constructed and cured in accordance with
applicable industry standards and slab design specifications.
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 10 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
3. An allowable vertical modulus of subgrade reaction (K,) of 60 tcf may be used for
design of concrete slabs bearing on a properly prepared fill section.
4. The floor slabs should be separated from all bearing walls and columns with slip
joints, which allow unrestrained vertical movement.
Joints should be observed periodically by the owner, particularly during the first
several years after construction. Slab movement can cause previously free -
slipping joints to bind. Measures should be taken to assure that slab isolation is
maintained in order to reduce the likelihood of damage to walls and other interior
improvements, including door frames, plumbing fixtures, etc.
5. Interior partitions resting on floor slabs should be provided with slip joints or
tracks so that if the slabs move, the movement cannot be transmitted to the
upper structure. This detail is also important for wallboards and doorframes. Slip
joints, which will allow at least 2 or more inches of vertical movement, should be
considered.
6. Concrete slab -on -grade floors should be provided with properly designed and
constructed control joints. ACI, AASHTO and other industry groups provide
guidelines for proper design and construction of concrete slabs -on- grade, and
associated jointing. The design and construction of such joints should account
for cracking resulting from concrete shrinkage, curling, tension and applied loads,
as well as other factors related to the proposed slab use. Joint layout based on
slab design may require more frequent, additional or deeper joints than typical
industry minimums, and should reflect the configuration and proposed use of the
slab. Particular attention in slab joint design should be given to areas where
slabs exhibit interior corners or curves, e.g., at column block -outs or reentrant
corners, and slabs with high length to width ratios, significant slopes, thickness
transitions, high traffic loads, or other unique features. The improper placement
or construction of control joints will increase the potential for slab cracking.
7. A floor slab should be adequately reinforced. Recommendations based on
structural considerations for slab thickness, jointing, and steel reinforcement in
floor slabs should be developed by a structural engineer.
8. Moisture can be introduced into a slab subgrade during construction and
additional moisture will be released from the slab concrete as it cures. GROUND
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 11 of 32
Subsurface Exploration Program
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Vail, Colorado
recommends placement of a properly compacted layer of free - draining gravel, 8
or more inches in thickness, beneath the slabs. This layer will help distribute
floor slab loadings, ease construction, reduce capillary moisture rise, and aid in
drainage. The free - draining gravel should contain less than 5 percent material
passing the No. 200 Sieve, more than 50 percent retained on the No. 4 Sieve,
and a maximum particle size of 2 inches.
The capillary break and the drainage space provided by the gravel layer also
may reduce the potential for excessive water vapor fluxes from the slab after
construction as mix water is released from the concrete.
We understand, however, that professional experience and opinion differ with
regard to inclusion of a free - draining gravel layer beneath slab -on -grade floors. If
these issues are understood by the owner and appropriate measures are
implemented to address potential concerns including slab curling and moisture
fluxes, then the gravel layer may be deleted.
EXTERIOR FLATWORK
Proper design, drainage, construction and maintenance of the areas surrounding the
proposed building and parking /driveway areas are critical to the satisfactory performance
of the project. Sidewalks, entranceway slabs and roofs, fountains, raised planters and
other highly visible improvements commonly are installed within these zones, and
distress in or near these improvements is common. Often, soil preparation in these
areas receives little attention because they fall between the building and pavement
(which are typically built with heavy equipment). Subsequent landscaping and
hardscape installation often is performed by multiple sub - contractors with light or hand
equipment, and over - excavation / soil processing is not performed. Therefore,
GROUND recommends that the design team, contractor, and pertinent subcontractors
take particular care with regard to proper subgrade preparation around the structure
exteriors.
Similar to slab -on -grade floors, exterior flatwork and other hardscaping placed on the
soils encountered on -site may experience post- construction movements due to volume
change of the subsurface soils and the relatively light loads that they impose. Both
vertical and lateral soil movements can be anticipated as the soils experience volume
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 12 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
change as the moisture content varies. Distress to rigid hardscaping likely will result.
The following measures will help to reduce damages to these improvements:
1. Ideally, subgrade soils beneath project sidewalks, paved entryways and patios,
masonry planters and short, decorative walls, and other hardscaping should be
placed on native sand and gravel material, or undocumented fill should be
removed and replaced with properly compacted fill. To perform like a slab -on-
grade floor, hardscaping should bear on a similar fill section as those discussed
for an (alternative) slab -on -grade floor.
2. Excavating to native gravels may not be feasible in all areas. Provided the owner
understands the risks identified above, the subgrade under exterior flatwork or
other (non - building) site improvements should be underlain by a section of
properly compacted fill at least 3 feet in thickness. This should occur prior to
placing any additional fill required to achieve finished design grades. We
estimate potential settlements on the order of 2+ inches with this processing
depth.
3. Increasing the processing depth may improve performance. The excavated soil
should be replaced as properly moisture - conditioned and compacted fill as
outlined in the Project Earthwork section of this report. As stated above, greater
depths of moisture - density conditioning of the subgrade soils beyond the above
minimum such as discussed may improve hardscape performance. Movement
will occur, some of which could be significant, especially if sufficient surface
drainage is not maintained.
4. Prior to placement of flatwork, a proof roll should be performed to identify areas
that exhibit instability and deflection. The soils in these areas should be removed
and replaced with properly compacted fill or stabilized.
5. Flatwork should be provided with effective control joints. Increasing the frequency
of joints may improve performance. ACI recommendations should be followed
regarding construction and /or control joints.
6. In no case should exterior flatwork extend to under any portion of the building
where there is less than two inches of clearance between the flatwork and any
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 13 of 32
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South Frontage Road East
Vail, Colorado
element of the building. Exterior flatwork in contact with brick, rock facades, or
any other element of the building can cause damage to the structure if the
flatwork experiences movements.
7. As discussed in the Surface Drainage section of this report, proper drainage also
should be maintained after completion of the project, and re- established as
necessary. In no case should water be allowed to pond on or near any of the site
improvements or a reduction in performance should be anticipated.
Concrete Scaling Climatic conditions in the project area including relatively low
humidity, large temperature changes and repeated freeze — thaw cycles, make it likely
that project sidewalks and other exterior concrete will experience surficial scaling or
spalling. The likelihood of concrete scaling can be increased by poor workmanship
during construction, such as `over- finishing' the surfaces. In addition, the use of de -icing
salts on exterior concrete flatwork, particularly during the first winter after construction,
will increase the likelihood of scaling. Even use of de -icing salts on nearby roadways,
from where vehicle traffic can transfer them to newly placed concrete, can be sufficient
to induce scaling. Typical quality control / quality assurance tests that are performed
during construction for concrete strength, air content, etc., do not provide information
with regard to the properties and conditions that give rise to scaling.
We understand that some municipalities require removal and replacement of concrete
that exhibits scaling, even if the material was within specification and placed correctly.
The contractor should be aware of the local requirements and be prepared to take
measures to reduce the potential for scaling and /or replace concrete that scales.
In GROUND's experience the measures below can be beneficial for reducing the
likelihood of concrete scaling. It must be understood, however, that because of the other
factors involved, including weather conditions and workmanship, surface damage to
concrete can develop, even where all of these measures were followed.
1) Maintaining a maximum water /cement ratio of 0.45 by weight for exterior
concrete mixes.
2) Include Type F fly ash in exterior concrete mixes as 20 percent of the
cementitious material.
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 14 of 32
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3) Specify a minimum, 28 -day, compressive strength of 4,500 psi for all exterior
concrete.
4) Include `fibermesh' in the concrete mix also may be beneficial for reducing
surficial scaling.
5) Cure the concrete effectively at uniform temperature and humidity. This
commonly will require fogging, blanketing and /or tenting, depending on the
weather conditions. As long as 3 to 4 weeks of curing may be required, and
possibly more.
6) Avoid placement of concrete during cold weather so that it is not exposed to
freeze -thaw cycling before it is fully cured.
7) Avoid the use of de -icing salts on given reaches of flatwork through the first
winter after construction.
We understand that commonly it may not be practical to implement some of these
measures for reducing scaling due to safety considerations, project scheduling, etc. In
such cases, additional costs for flatwork maintenance or reconstruction should be
incorporated into project budgets.
WATER- SOLUBLE SULFATES
The concentrations of water - soluble sulfates measured in selected sample retrieved
from the test holes was less than approximately 0.01 percent by weight. (See Table 1.)
Such concentrations of water - soluble sulfates represent a negligible degree of sulfate
attack on concrete exposed to these materials. Degrees of attack are based on the
scale of 'negligible,' 'moderate,' 'severe' and 'very severe' as described in the "Design
and Control of Concrete Mixtures," published by the Portland Cement Association
(PCA).
Based on these data GROUND, makes no recommendation for use of a special, sulfate -
resistant cement in project concrete.
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SOIL CORROSIVITY
The degree of risk for corrosion of metals in soils commonly is considered to be in two
categories: corrosion in undisturbed soils and corrosion in disturbed soils. The potential
for corrosion in undisturbed soil is generally low, regardless of soil types and conditions,
because it is limited by the amount of oxygen that is available to create an electrolytic
cell. In disturbed soils, the potential for corrosion typically is higher, but is strongly
affected by soil conditions for a variety of reasons but primarily soil chemistry.
A corrosivity analysis was performed to provide a general assessment of the potential for
corrosion of ferrous metals installed in contact with earth materials at the site, based on
the conditions existing at the time of GROUND's evaluation. Soil chemistry and physical
property data including pH, oxidation - reduction (redox) potential, sulfides, and moisture
content were obtained. Test results are summarized on Table 1.
Reduction - Oxidation Reduction and oxidation testing indicated negative potential: -72
millivolts. Such a low potentials typically creates a more corrosive environment.
Sulfide Reactivity Sulfide reactivity testing for the presence of sulfides indicated a
"trace" result in the on -site soils. The presence of sulfides suggests a more corrosive
environment.
pH Where pH is less than 4.0, soil serves as an electrolyte; the pH range of about 6.5 to
7.5 indicates soil conditions that are optimum for sulfate reduction. In the pH range
above 8.5, soils are generally high in dissolved salts, yielding a low soil resistivity'.
Testing indicated a pH value of approximately 8.1 in the local earth materials.
Soil Resistivity In order to assess the "worst case" for mitigation planning, samples of
materials retrieved from the test holes were tested for resistivity in the laboratory, after
being saturated with water, rather than in the field. Resistivity also varies inversely with
temperature.
Measurements of electrical resistivity indicated a value of approximately 4,327 ohm-
centimeters in a sample of the site earth materials.
The American Water Works Association (AWWA) has developed a point system scale
used to predict corrosivity. The scale is intended for protection of ductile iron pipe but is
1'3 American Water Works Association ANSI /AWWA C105/A21.5 -05 Standard
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Vail, Colorado
valuable for project steel selection. When the scale equals 10 points or higher,
protective measures for ductile iron pipe are recommended. The AWWA scale is
presented below. The soil characteristics refer to the conditions at and above pipe
installation depth.
TABLE A.1 SOIL -TEST EVALUATION 2
Soil Characteristic / Value Points
Resistivity
<1,500 ohm -cm .................................................................... .............................10
1,500 to 1,800 ohm -cm ......................................................... ..............................8
0 to +50 mV ...................................................................... ...............................
1,800 to 2,100 ohm -cm ......................................................... ..............................5
+50 to +100 mV ............................................................ ...............................
2,100 to 2,500 ohm -cm ......................................................... ..............................2
> +100 mV ................................................................ ...............................
2,500 to 3,000 ohm -cm ......................................................... ..............................1
Sulfide Content
>3,000 ohm -cm .......................................................... ..............................0
Positive.......................................................................... ...............................
pH
Trace................................................................................. ...............................
0 to 2.0 ............................................................................. ...............................
5
2.0 to 4.0 .......................................................................... ...............................
3
4.0 to 6.5 .......................................................................... ...............................
0
6.5 to 7.5 ....................................................................... ...............................
0 *
7.5 to 8.5 .......................................................................... ...............................
0
>8.5 ........................................................................... ...............................
3
Redox Potential
< 0 (negative values) ........................................................ ...............................
5
0 to +50 mV ...................................................................... ...............................
4
+50 to +100 mV ............................................................ ...............................
3'/2
> +100 mV ................................................................ ...............................
0
Sulfide Content
Positive.......................................................................... ...............................
3'/2
Trace................................................................................. ...............................
2
Negative............................................................................ ...............................
0
Moisture
Poor drainage, continuously wet ....................................... ............................... 2
Fair drainage, generally moist ....................................... ............................... 1
Good drainage, generally dry ........................................ ............................... 0
* If sulfides are present and low or negative redox - potential results (< 50 mV)
are obtained, add three points for this range.
We anticipate that drainage at the site after construction will be good. Based on the
values obtained for the soil parameters, the site soils appear to comprise a low corrosive
environment for metals (7 points).
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Corrosive conditions can be addressed by use of materials not vulnerable to corrosion,
heavier gauge materials with longer design lives, polyethylene encasement, or cathodic
protection systems. If additional information or recommendations are needed regarding
soil corrosivity, GROUND recommends contacting the American Water Works
Association or a Corrosion Engineer. It should be noted, however, that changes to the
site conditions during construction, such as the import of other soils, or the intended or
unintended introduction of off -site water, may alter corrosion potentials significantly.
PROJECT EARTHWORK
The project site has undergone previous grading for the existing building construction
and surrounding pedestrian walkways. We anticipate cuts up to 8 feet to construct the
addition and 2 feet for concrete walkway areas depending on the earthwork selected.
The following information is for private improvements; public roadways or utilities
should be constructed in accordance with applicable municipal / agency
standards.
General Considerations Site grading should be performed as early as possible in the
construction sequence to allow settlement of fills and surcharged ground to be realized
to the greatest extent prior to subsequent construction.
Prior to earthwork construction, vegetation and other deleterious materials should be
removed and disposed of off -site. Relic underground utilities should be abandoned in
accordance with applicable regulations, removed as necessary, and properly capped.
Topsoil present on -site should not be incorporated into ordinary fills. Instead, topsoil
should be stockpiled during initial grading operations for placement in areas to be
landscaped or for other approved uses.
Existing Fill Soils Actual contents and composition of the fill materials on -site generally
classified as clayey sand with gravels. Some of the excavated fill materials may not be
suitable for replacement as backfill. A geotechnical engineer should be retained during
site excavations to observe the excavated fill materials and provide recommendations
for its suitability for reuse.
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Use of Existing Native Soils Native soils that are free of trash, organic material,
construction debris, and other deleterious materials are suitable, in general, for
placement as compacted fill. Organic materials should not be incorporated into project
fills.
Fragments of rock, cobbles, and inert construction debris (e.g., concrete or asphalt)
larger than 3 inches in maximum dimension will require special handling and /or
placement to be incorporated into project fills. In general, such materials should be
placed as deeply as possible in the project fills. A geotechnical engineer should be
consulted regarding appropriate recommendations for usage of such materials on a
case -by -case basis when such materials have been identified during earthwork.
Standard recommendations that likely will be generally applicable can be found in
Section 203 of the current CDOT Standard Specifications for Road and Bridge
Construction.
Imported Fill Materials If it is necessary to import material to any of the sites, the
imported soils should be free of organic material and other deleterious materials.
Imported material for use as common fill should consist of soils that have less than 30
percent passing the No. 200 Sieve and should have a plasticity index of less than 10.
Representative samples of the materials proposed for import should be tested and
approved prior to transport to the site. "Pit run" material for use as common fill should be
approved prior to use.
Fill Platform Preparation Prior to filling, the top 8 to 12 inches of in -place materials on
which fill soils will be placed should be scarified, moisture conditioned and properly
compacted in accordance with the recommendations below to provide a uniform base for
fill placement. Where over - excavation is performed, these measures for subgrade
preparation apply to the subgrade surface at the base of the over - excavation depth.
If surfaces to receive fill expose loose, wet, soft or otherwise deleterious material,
additional material should be excavated, or other measures taken to establish a firm
platform for filling. The surfaces to receive fill must be effectively stable prior to
placement of fill.
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Fill Placement Fill materials should be thoroughly mixed to achieve a uniform moisture
content, placed in uniform lifts not exceeding 8 inches in loose thickness, and properly
compacted.
All soils should be compacted to 95 or more percent of the maximum dry density at
moisture contents within 2 percent of the optimum moisture content as determined by
ASTM D1557, the "modified Proctor."
No fill materials should be placed, worked, rolled while they are frozen, thawing, or
during poor /inclement weather conditions.
Care should be taken with regard to achieving and maintaining proper fill soil moisture
contents during placement and compaction. Soils with excessive moisture may exhibit
pumping, rutting, and deflection, and not compact effectively. The contractor should be
prepared to handle soils of this type, including using chemical stabilization, where
necessary.
Compaction areas should be kept separate, and no lift should be covered by another
until relative compaction and moisture content within the recommended ranges are
obtained.
Where soils supporting building floors or on which floors will be placed are exposed to
freezing temperatures or repeated freeze — thaw cycling during construction (commonly
due to water ponding on project soils) bearing capacity typically is reduced and /or
settlements increased due to the loss of density in the supporting soils. After periods of
freezing conditions, the contractor should re -work areas affected by the formation of ice
to re- establish adequate bearing support.
Use of Squeegee Relatively uniformly graded fine gravel or coarse sand, i.e.,
"squeegee," or similar materials commonly are proposed for backfilling foundation
excavations, utility trenches (excluding approved pipe bedding), and other areas where
employing compaction equipment is difficult. In general, GROUND does not recommend
this procedure for the following reasons:
1. Although commonly considered "self compacting," uniformly graded granular
materials require densification after placement, typically by vibration. The
equipment to densify these materials is not available on many job- sites.
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2. Even when properly densified, uniformly graded granular materials are
permeable and allow water to reach and collect in the lower portions of the
excavations backfilled with those materials. This leads to wetting of the
underlying soils and resultant potential loss of bearing support as well as
increased local heave or settlement.
GROUND recommends that wherever possible, excavations be backfilled with approved,
on -site soils placed as properly compacted fill. Where this is not feasible, use of
"Controlled Low Strength Material" (CLSM), i.e., a lean, sand - cement slurry ( "flowable
fill ") or a similar material for backfilling should be considered.
Where "squeegee" or similar materials are proposed for use by the contractor, the
design team should be notified by means of a Request for Information (RFI), so that the
proposed use can be considered on a case -by -case basis. Where "squeegee" meets
the project requirements for pipe bedding material, however, it is acceptable for that use.
Settlements Settlements will occur in filled ground, typically on the order of 1 to 2
percent of the fill depth. If fill placement is performed properly and is tightly controlled, in
GROUND's experience the majority (on the order of 60 to 80 percent) of that settlement
will typically take place during earthwork construction, provided the contractor achieves
the compaction levels recommended herein. The remaining potential settlements likely
will take several months or longer to be realized, and may be exacerbated if these fills
are subjected to changes in moisture content.
Cut and Filled Slopes Permanent site slopes supported by on -site soils up to 4 feet in
height may be constructed no steeper than 21/2:1 (horizontal : vertical). Minor raveling or
surficial sloughing should be anticipated on slopes cut at this angle until vegetation is
well re- established. Surface drainage should be designed to direct water away from
slope faces.
EXCAVATION CONSIDERATIONS
The test holes for the subsurface exploration were excavated to the depths indicated by
means of track - mounted, flight auger drilling equipment. We anticipate no significant
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excavation difficulties in the majority of the site with conventional heavy -duty excavation
equipment in good working condition.
We recommend that temporary, un- shored excavation slopes up to 8 feet in height be
cut no steeper than 11/2:1 (horizontal : vertical) in the site soils in the absence of
seepage. Sloughing on the slope faces should be anticipated at this angle. Local
conditions encountered during construction, such as groundwater seepage and loose
sand, will require flatter slopes. Stockpiling of materials should not be permitted closer
to the tops of temporary slopes than 5 feet or a distance equal to the depth of the
excavation, whichever is greater.
Should site constraints prohibit the use of the recommended slope angles, temporary
shoring should be used. The shoring should be designed to resist the lateral earth
pressure exerted by building, traffic, equipment, and stockpiles. GROUND can provide
shoring design upon request.
Good surface drainage should be provided around temporary excavation slopes to direct
surface runoff away from the slope faces. A properly designed drainage Swale should
be provided at the top of the excavations. In no case should water be allowed to pond at
the site. Slopes should also be protected against erosion. Erosion along the slopes will
result in sloughing and could lead to a slope failure.
Excavations in which personnel will be working must comply with all OSHA Standards
and Regulations. The contractor's "responsible person" should evaluate the soil
exposed in the excavations as part of the contractor's safety procedures. GROUND has
provided the information above solely as a service to The Town of Vail, and is not
assuming responsibility for construction site safety or the Contractor's activities.
BUS TRANSIT PLAZA
A pavement section is a layered system designed to distribute concentrated traffic loads
to the subgrade. Performance of the pavement structure is directly related to the
physical properties of the subgrade soils and traffic loadings. Because the project
pavements will be maintained by the city, the recommended pavement sections were
developed in general accordance with town specifications, the Colorado Department of
Transportation (CDOT) and local construction practice.
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Subgrade Materials Based on the results of our field and laboratory studies, the
subgrade soils in the area proposed for the bus transit station consisted predominantly
of non - plastic sands and gravels. These materials were classified typically as A -1 -13
soils in accordance with the AASHTO classification system, with Group Index value of 0.
Pavement Section We recommend that the bus route or other portions of the potential
areas for bus parking be provided with rigid pavements consisting of 6'/2 or more inches
of portland cement concrete. For superior performance, the concrete should be
underlain by 6 or more inches of properly compacted CDOT Class 6 Aggregate Base
Course. (A numerically equivalent composite section would be 6'/2 inches of asphalt over
11 inches of aggregate base, but that section would not perform as well as a rigid
section under heavy vehicle traffic and turning stresses.)
Pavement Materials Concrete pavements should consist of a plant mix composed of a
mixture of aggregate, portland cement and appropriate admixtures meeting the
requirements of a job -mix formula established by a qualified engineer as well as
applicable municipal design requirements. Concrete should have a minimum modulus of
rupture of third point loading of 650 psi. Normally, concrete with a 28 -day compressive
strength of 4,200 psi should develop this modulus of rupture value. The concrete should
be air - entrained with approximately 6 percent air and should have a minimum cement
content of 7 sacks per cubic yard. Maximum allowable slump should be 4 inches.
Concrete pavements should contain sawed or formed joints. CDOT and various industry
groups provide guidelines for proper design and concrete construction and associated
jointing. In areas of repeated turning stresses we recommend that the concrete
pavement joints be fully tied and doweled. We suggest that civil design consider joint
layout in accordance with CDOT's M standards, found at the CDOT website:
http:// www. dot.state.co.us /DesignSupport /.
These concrete mix design criteria should be coordinated with other project
requirements including the criteria for sulfate resistance presented in the Water - Soluble
Sulfates section of this report. To reduce surficial spalling resulting from freeze -thaw
cycling, we suggest that pavement concrete meet the requirements of CDOT Class P
concrete. In addition, the use of de -icing salts on concrete pavements during the first
winter after construction will increase the likelihood of the development of scaling.
Placement of flatwork concrete during cold weather so that it is exposed to freeze -thaw
cycling before it is fully cured also increases its vulnerability to scaling. Concrete placing
during cold weather conditions should be blanketed or tented to allow full curing.
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Depending on the weather conditions, this may result in 3 to 4 weeks of curing, and
possibly more.
The aggregate base material should meet the criteria of CDOT Class 6 aggregate base
course. Base course should be placed and compacted as recommended in the Project
Earthwork section of this report.
Subgrade Preparation Although subgrade preparation to a depth of 8 to 12 inches is
typical in the project area, pavement performance commonly can be improved by a
greater depth of moisture - density conditioning of the soils.
Remedial Earthwork GROUND recommends that shortly before paving, the pavement
subgrade be excavated and /or scarified to a depth of at least 2 feet, moisture -
conditioned and properly re- compacted. Recommendations for fill placement and
compaction are provided in the Project Earthwork section of this report. The contractor
should be prepared either to dry the subgrade materials or moisten them, as needed,
prior to compaction.
Subgrade preparation should extend the full width of the pavement from back -of -curb to
back -of -curb. The subgrade for sidewalks and other project hardscaping also should be
prepared in the same manner.
Where adequate drainage cannot be achieved or maintained, a greater depth of
excavation and replacement is recommended, in addition to the edge drains
recommended below.
Proof Rolling Immediately prior to paving, the subgrade should be proof rolled with a
heavily loaded, pneumatic tired vehicle. Areas where water that show excessive
deflection during proof rolling should be excavated and replaced and stabilized. Areas
allowed to pond prior to paving will require significant re- working prior to proof - rolling.
Passing proof - rolling is an additional requirement for pavement subgrade soils; it may be
possible for soils to be compacted within the limits indicated in the Project Earthwork
section of this report and fail proof rolling, particularly in the upper range of
recommended moisture contents.
Subgrade Stabilization Because of the sandy nature of some of the site soils, they may
"pump" or deflect during compaction and proof - rolling if moisture levels are not carefully
controlled and achieving a stable platform for paving may be difficult. Chemical
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stabilization of the pavement subgrade may be necessary. Because of the water - soluble
sulfates in the site soils, stabilization with lime does not appear feasible. We anticipate,
however, that stabilization with portland cement would be effective.
It is not possible to assess subgrade stability reliably on the basis of information during
geotechnical exploration or subsequent laboratory testing. It is often our experience that
where an existing pavement is removed, the underlying subgrade exhibits instability
when subjected to construction and /or traffic loading, even where testing suggests
otherwise acceptable moisture contents and density. Therefore, it may be necessary to
stabilize the majority of the existing subgrade prior to repaving. This may require
reprocessing or chemical stabilization of existing soils or removal and replacement with
other site materials or imported soil. Our office should be retained to observe the
subgrade condition and stability during the removal process. If additional or more
specific information is required, then we suggest additional exploration be performed
along the proposed roadway.
Drainage and Maintenance The collection and diversion of surface drainage away
from paved areas is extremely important to satisfactory performance of the pavement.
The subsurface and surface drainage systems should be carefully designed to ensure
removal of the water from paved areas and subgrade soils. Where topography, site
constraints or other factors limit or preclude adequate surface drainage, pavements
should be provided with edge drains to reduce loss of subgrade support. The long -term
performance of the pavement also can be improved greatly by proper backfilling and
compaction behind curb, gutter, and sidewalk. Unless the interceptor drain and edge
drains (where included) are installed properly and maintained, and site drainage in
general is well maintained, there is an increased risk of poor pavement performance at
this site due to the expansive subgrade materials and the local introduction of off -site
irrigation water.
Landscape irrigation in planters adjacent to pavements and in "island" planters within
paved areas should be carefully controlled or differential settlement and /or rutting of the
nearby pavements will result. Drip irrigation systems are recommended for such
planters to reduce over -spray and water infiltration beyond the planters. Enclosing the
soil in the planters with plastic liners and providing them with positive drainage also will
reduce differential moisture increases in the surrounding subgrade soils. In our
experience, infiltration from planters adjacent to pavements is a principal source of
moisture increase beneath those pavements. This wetting of the subgrade soils from
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infiltrating irrigation commonly leads to loss of subgrade support for the pavement with
resultant accelerating distress, loss of pavement life and increased maintenance costs.
This is particularly the case in the later stages of project construction after landscaping
has been emplaced but heavy construction traffic has not ended. Heavy vehicle traffic
over wetted subgrade commonly results in rutting and pushing of flexible pavements,
and cracking of rigid pavements. In relatively flat areas where design drainage gradients
necessarily are small, subgrade settlement can obstruct proper drainage and yield
increased infiltration, exaggerated distress, etc. (These considerations apply to project
flatwork, as well.)
Also, GROUND's experience indicates that longitudinal cracking is common in asphalt -
pavements generally parallel to the interface between the asphalt and concrete
structures such as curbs, gutters or drain pans. This of this type is likely to occur even
where the subgrade has been prepared properly and the asphalt has been compacted
properly.
The anticipated traffic loading does not include excess loading conditions imposed by
heavy construction vehicles. Consequently, heavily loaded concrete, lumber, and
building material trucks can have a detrimental effect on the pavement. In areas where
the maintenance traffic is turning, concrete pavement is recommended.
As noted above, the standard care of practice in pavement design describes the
recommended flexible pavement section as a "20- year" design pavement; however,
most pavements will not remain in satisfactory condition without regular maintenance
and rehabilitation procedures performed throughout the life of the pavement.
Maintenance and rehabilitation measures preserve, rather than improve, the structural
capacity of the pavement structure. Therefore, GROUND recommends that an effective
program of regular maintenance be developed and implemented to seal cracks, repair
distressed areas. The greatest benefit of pavement overlaying will be achieved by
overlaying sound pavements that exhibit little or no distress.
Crack sealing should be performed at least annually. After approximately 8 to 10 years
after construction, patching and additional crack sealing may be required. Prior to
overlays, it is important that all cracks be sealed with a flexible, rubberized crack sealant
in order to reduce the potential for propagation of the crack through the overlay. If actual
traffic loadings exceed the values used for development of the pavement sections,
however, pavement maintenance measures will be needed on an accelerated schedule.
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SURFACE DRAINAGE
The following drainage measures are recommended for design, construction, and should
be maintained at all times after the project has been completed:
1) Wetting or drying of foundation and underslab areas should be avoided.
Permitting increases /variations in moisture to the adjacent or supporting soils
may result in a decrease in bearing capacity and an increase in volume change
of the underlying soils and /or differential movement.
2) Positive surface drainage measures should be provided and maintained to
reduce water infiltration into foundation soils. The ground surface surrounding
the exterior of the building should be sloped to drain away from the foundation in
all directions. We recommend a minimum slope of 12 inches in the first 10 feet in
areas not covered with pavement or concrete slabs, or a minimum 3 percent in
the first 10 feet in the areas covered with pavement or concrete slabs. Reducing
the slopes to comply with ADA requirements may be necessary but may result in
an increased potential for moisture infiltration and subsequent volume change of
the underlying soils. In no case should water be allowed to pond near or
adjacent to foundation elements. However, if positive surface drainage is
implemented and maintained directing moisture away from the building, lesser
slopes can be utilized if the risk of incrementally greater settlements is accepted.
In no case should water be allowed to pond near or adjacent to foundation
elements, or on sidewalks, hardscaping, or other improvements as well as utility
trench alignments, which are likely to be adversely affected by moisture - volume
changes in the underlying soils or flow of infiltrating water.
Drainage measures also should be included in project design to direct water
away from sidewalks and other hardscaping as well as utility trench alignments
which are likely to be adversely affected by moisture - volume changes in the
underlying soils or flow of infiltrating water. Routine maintenance of site drainage
should be undertaken throughout the design life of the project.
In GROUND's experience, it is common during construction that in areas of
partially completed paving or hardscaping, bare soil behind curbs and gutters,
and utility trenches, water is allowed to pond after rain or snow -melt events.
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Wetting of the subgrade can result in loss of subgrade support and increased
settlements / increase heave. By the time final grading has been completed,
significant volumes of water can already have entered the subgrade, leading to
subsequent distress and failures. The contractor should maintain effective site
drainage throughout construction so that water is directed into appropriate
drainage structures.
3) Roof downspouts and drains should discharge well beyond the perimeter of the
structure's foundation, or be provided with positive conveyance off -site for
collected waters. Downspouts should not discharge into a building underdrain
system.
4) Landscaping which requires watering should be located 10 or more feet from the
building perimeter. Irrigation sprinkler heads should be deployed so that applied
water is not introduced into foundation soils. Landscape irrigation should be
limited to the minimum quantities necessary to sustain healthy plant growth.
Use of drip irrigation systems can be beneficial for reducing over -spray beyond
planters. Drip irrigation also can be beneficial for reducing the amounts of water
introduced to building foundation soils, but only if the total volumes of applied
water are controlled with regard to limiting that introduction. Controlling rates of
moisture increase beneath the foundations and floors should take higher priority
than minimizing landscape plant losses.
Where plantings are desired within 10 feet of the building, GROUND
recommends that the plants be placed in water -tight planters, constructed either
in- ground or above - grade, to reduce moisture infiltration in the surrounding
subgrade soils. Planters should be provided with positive drainage and
landscape underdrains.
5) We do not recommend the use of plastic membranes to cover the ground surface
near the building without careful consideration of other components of project
drainage. Plastic membranes can be beneficial to directing surface waters away
from the building and toward drainage structures. However, they effectively
preclude evaporation or transpiration of shallow soil moisture. Therefore, soil
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moisture tends to increase beneath a continuous membrane. Where plastic
membranes are used, additional shallow, subsurface drains should be installed.
FOUNDATION WALLS
Foundation walls that are laterally supported and can be expected to undergo only a
limited amount of deflection, i.e., an "at- rest" condition, should be designed to resist
lateral earth pressures computed on the basis of an equivalent fluid unit weight of 55 pcf
if imported, select, granular, structural backfill (meeting the criteria presented below) is
used to backfill the walls. The at -rest lateral earth pressures should be computed using
an equivalent fluid unit weight of 65 pcf where on -site materials are used as backfill.
The loads recommended above are for well- drained conditions with a horizontal upper
backfill surface. The additional loading of an upward sloping backfill, hydrostatic loads if
sufficient drainage is not provided, as well as loads from traffic, stockpiled materials,
etc., should be included in foundation wall design.
GROUND recommends use of structural backfill behind the walls to achieve lower lateral
earth pressures. To realize the lower equivalent fluid unit weight, structural fill should be
placed behind the wall to a minimum distance equal or greater than half of the wall
height. Where structural backfill is used, the upper 1 foot of the wall backfill should be a
relatively impermeable soil or otherwise protected to reduce surface water infiltration into
the backfill.
Backfill soils should be thoroughly mixed to achieve a uniform moisture content, placed
in uniform lifts not exceeding 6 inches in loose thickness, and properly compacted in
accordance with the recommendations in the Site Grading section of this report. The
contractor should take care not to over - compact the backfills, which could result in
excessive lateral pressures on the walls.
Some settlement of wall backfills will occur even where the material was placed
correctly. This settlement likely will be differential, increasing with depth of fill. Where
shallowly founded structures and pavements must be placed on backfilled zones,
structural design, pipe connections, etc., should take into account backfill settlement,
including differential movement and the associated risks are understood. A geotechnical
engineer should be retained to provide recommendations for founding improvements in
such areas.
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CLOSURE
Geotechnical Review The author of this report should be retained to review project
plans and specifications to evaluate whether they comply with the intent of the
recommendations in this report. The review should be requested in writing.
The geotechnical recommendations presented in this report are contingent upon
observation and testing of project earthworks by representatives of GROUND. If another
geotechnical consultant is selected to provide materials testing, then that consultant
must assume all responsibility for the geotechnical aspects of the project by concurring
in writing with the recommendations in this report, or by providing alternative
recommendations.
Materials Testing The Town of Vail should consider retaining a geotechnical engineer
to perform materials testing during construction. The performance of such testing or lack
thereof, in no way alleviates the burden of the contractor or subcontractor from
constructing in a manner that conforms to applicable project documents and industry
standards. The contractor or pertinent subcontractor is ultimately responsible for
managing the quality of their work; furthermore, testing by the geotechnical engineer
does not preclude the contractor from obtaining or providing whatever services they
deem necessary to complete the project in accordance with applicable documents.
Limitations This report has been prepared for The Town of Vail as it pertains to the
proposed concert hall addition and 'transit plaza' bus pull out as described herein. It
may not contain sufficient information for other parties or other purposes. The owner or
any prospective buyer relying upon this report must be made aware of and must agree
to the terms, conditions, and liability limitations outlined in the proposal.
In addition, GROUND has assumed that project construction will commence by Summer
2012. Any changes in project plans or schedule should be brought to the attention of a
geotechnical engineer, in order that the geotechnical recommendations may be re-
evaluated and, as necessary, modified.
The geotechnical conclusions and recommendations in this report relied upon
subsurface exploration at a limited number of exploration points, as shown in Figure 1,
as well as the means and methods described herein. Subsurface conditions were
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interpolated between and extrapolated beyond these locations. It is not possible to
guarantee the subsurface conditions are as indicated in this report. Actual conditions
exposed during construction may differ from those encountered during site exploration.
If during construction, surface, soil, bedrock, or groundwater conditions appear to be at
variance with those described herein, a geotechnical engineer should be advised at
once, so that re- evaluation of the recommendations may be made in a timely manner. In
addition, a contractor who relies upon this report for development of his scope of work or
cost estimates may find the geotechnical information in this report to be inadequate for
his purposes or find the geotechnical conditions described herein to be at variance with
his experience in the greater project area. The contractor is responsible for obtaining
the additional geotechnical information that is necessary to develop his workscope and
cost estimates with sufficient precision. This includes current depths to groundwater,
etc.
The materials present on -site are stable at their natural moisture content, but may
change volume or lose bearing capacity or stability with changes in moisture content.
Performance of the proposed structure and pavement will depend on implementation of
the recommendations in this report and on proper maintenance after construction is
completed. Because water is a significant cause of volume change in soils and rock,
allowing moisture infiltration may result in movements, some of which will exceed
estimates provided herein and should therefore be expected by the owner.
This report was prepared in accordance with generally accepted soil and foundation
engineering practice in the project area at the date of preparation. GROUND makes no
warranties, either expressed or implied, as to the professional data, opinions or
recommendations contained herein. Because of numerous considerations that are
beyond GROUND's control, the economic or technical performance of the project cannot
be guaranteed in any respect.
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 31 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
GROUND appreciates the opportunity to complete this portion of the project and
welcomes the opportunity to provide The Town of Vail with a proposal for construction
observation and materials testing prior to construction commencement when design
plans have been completed.
Sincerely,
GROUND Engineering Consultants, Inc.
Scott W. Richards, P.E.
Reviewed by Brian H. Reck, P.G., C.E.G. fD
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 32 of 32
Subsurface Exploration Program
Proposed Bus / Vehicle Pull Out
South Frontage Road East
Vail, Colorado
GOOGLE EARTH AERIAL IMAGE (DATE UNKNOWN) alm0um
1 ENSINBERINi CONOMT/INTS
Indicates test hole number and approximate location. LOCATION OF TEST HOLES
(Not to Scale)
Job No. 11 -6024 GROUND Engineering Consultants, Inc. Page 33 of 32
Test Hole Test Hole
1 2
0
303 1 B/15/13
5
5/12 16/12
4111114
N
t
10
a
25/12
15
20
almoumn
EN31NEE1'IINB CONSU LTANTS
LOGS OF TEST HOLES
JOB NO.: 11 -6024 FIGURE: 2
CADFILE NAME:6024LOG.DWG
LEGEND:
® Asphalt
Base Course
Fill: Clayey gravelly sand, loose, moist, and dark brown in color.
Sand and Gravel: With scattered cobbles and possible boulders, stratified layers, medium to coarse
grained, sub - angular gravels, medium dense to very dense, moist to very moist, and brown in color.
PDrive sample, 2 -inch I.D. California liner sample Drive sample, 1 -3/8 inch I.D. standard sample
23/12 Drive sample blow count, indicates 23 blows of a 140 -pound hammer falling 30 inches were
required to drive the sampler 12 inches.
20/25/30 Drive sample blow count, indicates 20, 25, and 30 blows of a 140 -pound hammer falling 30 inches were
required to drive the sampler 18 inches.
NOTES:
1) Test holes were drilled on 11/11/11 with 4 -inch diameter continuous flight power augers.
2) Locations of the test holes were measured approximately by pacing from features shown on
the site plan provided.
3) Elevations of the test holes were not measured and the logs of the test holes are drawn to
depth.
4) The test hole locations and elevations should be considered accurate only to the degree
implied by the method used.
5) The lines between materials shown on the test hole logs represent the approximate
boundaries between material types and the transitions may be gradual.
6) Groundwater was not encountered during drilling. Groundwater levels can fluctuate seasonally
and in response to landscape irrigation.
7) The material descriptions on this legend are for general classification purposes only.
See the full text of this report for descriptions of the site materials and related recommendations.
GROMM
ENGINEERING CONSULTRNT5
LEGEND AND NOTES
JOB NO.: 11 -6024 FIGURE: 3
CADFILE NAME: 6024LEG.DWG
8
-7
6
Consolidation
with Constant Pressure
U on Wettin
4
2
J
W
ai
0
eE
Z
O
r
2
0
J
0
4
O
U
6
8
10
0.1
1.0
10 100
APPLIED PRESSURE - ksf
Moisture Content = 3.9 percent
Dry Unit Weight = 118.7 pcf
Sample of: Sandy Silty Gravel
From: Test Hole 1 at 14 ft
GROUND
ENGINEERONG CONSULTRNTS
SWELL- CONSOLIDATION
TEST RESULTS
JOB NO.: 11 -6024 FIGURE: 4
CADFILE NAME: 6024SWL01.DWG
4
-7
3
Consolidation
with Constant Pressure
Upon Wetting
2
1
�J
in
0
2
O
6
1
O
O
2
O
U
3
4
5
0.1
1.0
10 100
APPLIED PRESSURE - k9f
Moisture Content = 6.6 percent
Dry Unit Weight = - pcf
Sample of Silty Sand
From: Test Hole 2 at 5 ft
GROUND
ENGINEERONG CONSULTRNTS
SWELL- CONSOLIDATION
TEST RESULTS
JOB NO.: 11 -6024 FIGURE: 5
CADFILE NAME: 6024SWL02.DWG
7-,A
m