HomeMy WebLinkAboutGeotechnical Engineering Report 07.19.2017Air CTLITHOMPSON
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July 19, 2017
Phil Vaughan Construction Management, Inc.
1038 County Road 323
Rifle, CO 81650
Attention: Mr, Phil Vaughan
Subject: Geotechnical Engineering Consultation
Garage Building
Vaughan Residence
1038 County Road 323
Garfield County, Colorado
Project No. GS05694.000-145
This letter provides our geotechnical recommendations for the planned
garage building to be constructed at 1038 County Road 323 in Garfield County,
Colorado. Planned building construction, anticipated subsurface conditions, and
our foundation recommendations for the building are provided below.
Planned Construction
The garage will have plan dimensions of 30 feet by 86 feet. Walls will be
framed with 2 x 6 wood studs and the roof system will be comprised of wood trusses
that span across the shorter dimension. The building will have five overhead doors
on the south wall, providing access to four parking bays. The finished floor slab
elevation in the building will be 5309 feet. Existing ground surface within the building
footprint varies from about 5307 to 5310. The preferred foundation is a concrete
slab -on -ground with turned down edges.
Subsurface Conditions
Subsurface conditions are anticipated to be similar to those observed in
exploratory pits excavated as part of our field investigation for a 2004 addition to the
Vaughan Residence. Subsurface conditions consisted of 2.5 and 6 feet of silty
sandy clay underlain by clayey to silty gravel with basalt cobbles and boulders to the
total explored depth of 7.5 feet below existing ground surface. Free ground water
was not observed in the exploratory pits.
Site Earthwork
Stripping depth will likely average about 6 inches to remove topsoil and
organics from below the planned building. We believe fill thickness of 2 feet or Tess
will be required to achieve subgrade for finished floor. Significant overlot grading
cuts and fill are not anticipated for building pad construction.
234 Center Drive { Glenwood Springs, Colorado 81601
Telephone: 970-945-2809 Fax: 970-945-7411
Excavations for utilities and foundation walls can be accomplished using
conventional, heavy-duty construction equipment. Excavation sides will need to be
stoped or braced to meet local, stat: and federal safety regulations. We believe the
clay will classify as a Type B soil and the gravel will classify as a Type C soil based
on OSHA standards governing excavations. Temporary slopes deeper than 4 feet (if
required) should be no steeper than 1 to 1 (horizontal to vertical) in Type B soils and
1.5 to 1 in Type C soils. Contractors should identify the soils encountered in the
excavations and refer to OSHA standards to determine appropriate slopes.
Structural Fill
The silty sandy clay soil at this site possesses the potential for moderate
consolidation when wetted under load. We recommend placement of at least 1 foot
of structural fill below the slab -on -ground foundation. We recommend the granular,
structural fill consist of an aggregate base course, such as a CDOT Class 6 or
similar soil.
The subgrade surface that will support structural fill should be scarified to a
depth of at least 6 inches, moisture -treated, and compacted. Structural fill should be
moisture -treated to within 2 percent of optimum moisture content and compacted to
at least 98 percent of maximum standard Proctor (ASTM D 698) dry density. Water
required to increase the structural fill soil moisture content to the specified moisture
content should be uniformly mixed into the fill soil prior to compaction. We
recommend loose fill lifts of 10 inches or less. The actual thickness of fill sifts that
can be properly compacted will depend on the type of compaction equipment.
Slab -on Ground
In our opinion, a slab -on -ground is a reasonable system for the foundation
and floor of the proposed garage at this site. We recommend supporting the
slab on a 1 -foot thickness of densely -compacted, granular structural fill. Design
criteria for a slab -on -ground foundation/floor system are provided below.
1. The slab -on -ground foundation should be constructed on a
minimum 1 -foot thickness densely -compacted, granular structural
fill.
2. The slab should be heavily reinforced and preferably in a single
monolithic configuration to help maintain its integrity in the event of
ground movement. The slab turned down edges should be
designed for a maximum allowable soil pressure of 1,500 psf.
3. Modulus of subgrade reaction (Ks) is normally used for a slab -on -
ground design. The modulus of subgrade reaction is dependent
upon the compressibility of the foundation soils and the size (or
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
PROJECT NO. GS05694.000-145
C:lllssrslcdowning19ox1Projects1Glenwood Springs - ProJects1GS05694.000114613. Letters1GS05694.000 146 L2.docx
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effective loaded area) of the foundation. If the entire slab
foundation is uniformly loaded, then a KS value of 200 pci. A friction
coefficient of 0.45 can be used for lateral resistant between
concrete and granular structural fill.
4. Lateral Toads can be resolved by evaluating passive resistance
using an equivalent fluid density of 325 pcf for the onsite soils,
provided the backfill is compacted and is not removed.
5. Soils beneath the foundation must be protected from freezing. The
granular structural fill and natural soils are not significantly
susceptible to frost heave. We recommend the perimeter of the
slab be turned down to extend at least 24 inches below exterior
grade. The Garfield County building department should be
contacted for specific frost depth requirements.
Surface Drainage
Surface drainage is critical to the performance of building foundations and
slabs. Proper surface drainage can help control the amount of surface water
that penetrates and wets the subgrade soils below the slab. The ground surface
surrounding the building should be sloped to drain away from the building in all
directions. Roof gutters and downspouts should be provided.
Limitations
This geotechnical engineering consultation was provided in a manner
consistent with that level of care and skill ordinarily exercised by geotechnical
engineers currently practicing under similar conditions in the locality of this
project. No warranty, express or implied, is made. If we can be of further
service in discussing the contents of this report, please call.
Very truly yours
cc: Via email to phik pvcmi.com
Reviewed by:
es D. Kellogg, P.E.
'vision Manager
PHIL VAUGHAN CONSTRUCTION MANAGEMENT
VAUGHAN RESIDENCE ADDITION
PROJECT NO. GS05894.000-145
C:1UeerslcdowningiSox112rojccls1Glenwood Springs • Projocts1GS06694.000114613. Letters1GS05694.000 145 L2.docx
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