HomeMy WebLinkAbout20180829163009882_1.pdf DrjirR\mi 5020 County Road 154
Glenwood Springs,CO 81601
Geotechnical Engineering I Engineering Geology Phone:(970)945-7988
Materials Testing I Environmental Fax:(970)945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Denver(HQ),Parker,Colorado Springs,Fort Collins,Glenwood Springs,Summit County,Colorado
August 8, 2018
Last Ridge Development
Attn: Gary Manchester
1720 Wazee,#5D
Denver, Colorado 80202
garymanchester@haselden.com
Project No. 17-7-497
Subject: Observation of Excavation,Proposed Duplex Residence,Lot 16,Block 9,Vail
Intermountain,2794 Snowberry Drive, Vail, Colorado
Dear Gary:
As requested, a representative of H-P/Kumar observed the excavation at the subject site on
August 1, 2018 to evaluate the soils exposed for foundation support. The findings of our
observations and recommendations are presented in this report. The services were performed in
accordance with our agreement for professional engineering services to Last Ridge Development
dated July 31,2018.
Background Information: Hepworth-Pawlak Geotechnical previously performed a review of
the site conditions at the lot and presented the findings in a report dated February 23,2016,
Job No. 115 596A. That report discussed the deeper excavation cuts at the site could be shored
with a permanent soil nail wall system for stability of the hillside.
Proposed Construction: The building will be a three story structure cut into the hillside.
Ground floors will be slab-on-grade. The building has been designed to be supported on spread
footings using an allowable soil bearing pressure of 2,500 psf based on information the soils
report for the adjacent Lot 15. The hillside cut for the proposed building has been retained with
a permanent type soil nail wall designed and built by HTM Construction,design plans dated
April 2, 2018. The soil nail wall is up to about 24 feet high. We assume the soil nail wall was
designed for both global and local stability.
Site Observations: At the time of our site visit,the foundation excavation was essentially
complete and had been cut in three levels from about 3 to 24 feet below the adjacent ground
surface. Steps in grade between the excavation levels ranged from about 1 to 3 feet. The deeper
cuts were along the south and east sides of the excavation were where the soil nail wall had been
constructed. The soils exposed in the bottom of the excavation consisted of medium dense to
dense, silty sandy to very sandy gravel with cobbles to about 6-inch maximum size. The
excavation subgrade had been compacted. The soils were too rocky to obtain undisturbed
samples for swell-
Last Ridge Development
August 8, 2018
Page 2
consolidation testing. The results of a gradation analysis performed on a disturbed bulk sample
of the granular soils(minus 3-inch fraction)obtained from the site are presented on Figure 1.
The plus 3-inch portion of the exposed soils was estimated at about 20 to 25%. There was some
water seepage from the soil nail wall in the southwest portion of the excavation. The exposed
soils were slightly moist to moist, and very moist in the seepage areas.
Recommendations: Considering the conditions exposed in the excavation and the nature of the
proposed construction,spread footings placed on the undisturbed natural granular soils designed
for an allowable bearing pressure of 2,500 psf can be used for support of the proposed building
with some risk of differential settlement. The risk of differential settlement is due primarily to
the variable cut depths and assumed variable structural loadings.
Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns.
Loose and disturbed soils in footing areas should be removed and the bearing level extended
down to the undisturbed natural granular soils,and the subgrade re-compacted as needed. The
water seepage into the excavation should be collected and diverted away from the footing areas
and any softened soils and mud removed before concrete placement. Exterior footings should be
provided with adequate soil cover above their bearing elevations for frost protection. Continuous
foundation walls should be well reinforced top and bottom to span local anomalies such as by
assuming an unsupported length of at least 12 feet. Foundation walls up to about 12 feet tall
acting as retaining structures should also be designed to resist a lateral earth pressure based on an
equivalent fluid unit weight of at least 50 pcf for on-site soil,excluding oversized(plus 6 inch)
rocks as backfill. A perimeter foundation drain should be provided to prevent temporary buildup
of hydrostatic pressure behind the basement walls and prevent wetting of the lower level. The
drain system should include at least 4 inches of free draining gravel below the floor slabs.
Structural fill placed within floor slab areas can consist of the on-site granular soils,excluding
oversized (plus 4 inch)rocks, compacted to at least 95%of standard Proctor density (SPD) at a
moisture content near optimum. Backfill placed around the structure should be compacted to at
least 90% SPD(95%in pavement areas) and the surface graded to prevent ponding within at
least 10 feet of the building. Some settlement of deep foundation wall backfill could occur even
though the fill is compacted as recommended which could result in distress to facilities
constructed on the fill. Landscape that requires regular heavy irrigation, such as sod, and
sprinkler heads should not be located within 10 feet of the foundation.
Limitations: The recommendations submitted in this letter are based on our observation of the
soils exposed within the foundation excavation and do not include subsurface exploration to
evaluate the subsurface conditions within the loaded depth of foundation influence. This study is
based on the assumption that soils beneath the footings have equal or better support than those
exposed. The risk of foundation movement may be greater than indicated in this report because
of possible variations in the subsurface conditions. In order to reveal the nature and extent of
H-PKUMAR
Project No. 17-7-497
Last Ridge Development
August 8,2018
Page 3
variations in the subsurface conditions below the excavation,drilling would be required. It is
possible the data obtained by subsurface exploration could change the recommendations
contained in this letter.
Our services do not include determining the presence,prevention or possibility of mold or other
biological contaminants(MOBC)developing in the future. If the client is concerned about
MOBC,then a professional in this special field of practice should be consulted.
If you have any questions or need further assistance,please call our office.
Sincerely, - ,40,q`-)091014,
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attachment Figuie-1, Gradation Test Results
cc: Slopeside Construction—Mike Dantas (mike.dantas67@gmail,com)
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Project No. 17-7-497