HomeMy WebLinkAboutB16-0243.001 Engineering letter.pdft:>1 6 -0 d-l(3 . 0 c f
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~~rnr~w[~ ~ 5020 County Road 1 S4
lenwood Springs, CO 81601
NOV o 2 2016 ...
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. Phone: (970) 945-7988
..._TOWN OF VAi~.:---·-·~_/ Fax: (910> 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado
October 24, 2016
Keith Novick
122 W. Timber Draw
Edwards, Colorado 81632
Project No. 16-7-477
Subject: Preliminary Findings of Excavation Observation, Proposed Residence, Lot 22,
Filing 1, Vail Village West, 1740 Sierra Trail, Vail, Colorado
Dear Keith:
As requested, representatives of HP/Kumar observed the excavation at the subject site on several
visits between September 19 and October 18, 2016 to evaluate the soils exposed for foundation
support. The findings of our observations and preliminary recommendations for the foundation
design are presented in this report. The services were performed as part of our agreement for
professional engineering services to you, dated September 23, 2016. Additional site visits wiII
be needed to confirm the soil bearing condition-, as the excavatmn progresses.
Proposed Construction: The residence will be 1 multi le\ el structure cut into and stepped
down the hillside slope to the north. The uphill cut has been shored with a soil nail wall up to
about 22 feet in height. The building wru, ongmally designed to be supported on micro-piles ai;
recommended by CTL Thompson in their report dated Anl 7, 2014, Project No. GS05840-145.
We have been provided a copy of that report It has been requested we evaluate the soils
exposed in the excavation for a spread footing foundation system to support the residence.
Site Observations: At the time of this report, the excav.ition was partially complete with the
southern portion dug at one level up to about 22 feet high daylightmg to the north. The soils
exposed in the bottom of the completed portion of the exca\ ation consist primarily of generally
medium dense, clayey to very clayey sandy gravel with cobbles. There was some fill around the
old foundation in about the middle of the excavation where the step down change in grade is
planned. Initially no free Wc.lter was encountered in the excavc.ttion; however, after drilling of
several micro-piles below the proposed south wc.tll foundation, groundwater seepage is now
entering the excavation. The soils were moist to wet in the ponded groundwater areas.
Preliminary Recommendations: Considering the condit10ni; exposed in the excavation, our
experience in the area and the nature of the propo~ed coni;truction, we believe spread footings
placed on the undisturbed natural ~oil designed for an allowable bearing pressure of 2,500 psf
can be used for support of the propoi;ed rei;idence. The alk:wable soil bearing pressure can be
increased by 1 1 for eccentric loading conditions provided the rei,ultant of all forces acts within
Keith Novick
October 24, 2016
Page 2
the central third of the footing section. Footings should be a minimum width of 18 inches for
continuous walls and 2 feet for columns. The water seepage into the excavation should be
collected and diverted away from the footing areas and any fill, softened soils and mud removed
before concrete placement. It may be necessary to sub-excavate soft wet subgrade areas and
replace with a depth of crushed screened rock to stabilize prior to the footing construction.
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
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 imported screened rock as backfill. The lateral
resistance of foundation or retaining wall footings will be a combination of the sliding resistance
of the footing on the foundation materials and passive earth pressure against the side of the
footing. Resistance to sliding at the bottoms of the footings can be calculated based on a
coefficient of friction of 0.45. Passive pressure of compacted backfill against the sides of the
footings can be calculated using an equivalent fluid unit weight of 350 pcf for moist condition.
The coefficient of friction and passive pressure values recommended above assume ultimate soil
strength and suitable factors of safety should be included in the design to limit the strain which
will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed
against the sides of the footings to resist laternl loads should be a suitable granular material
compacted to at least 95% of the maximum standard Proctor density at a moisture content near
optimum.
A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic
pressure behind the basement walls and prevent wetting of the lower levels. The drain system
should include at least 6 inches of drain gravel below the floor slabs. One or more interior lateral
drains below the basement floors may also be needed. Structural fill placed within floor slab
areas can consist of the on-site granular soils, or suitable imported granular soils such as road
base, compacted to at least 95% of standard Proctor density at a moisture content near optimum.
Backfill placed around the structure should be compacted and the surface graded to prevent
ponding within at least 10 feet of the building. Some settlement of deep backfill should be
expected.
We should observe the !-toils exposed as the exc.i.vation proceeds to further evaluate the footing
bearing conditions.
Limitations: The recommendations submitted in this letter are based on our observation of the
soils expo~ed within the foundation excavation and do not include subsurface exploration to
evaluate the subsurface conditions within the loaded depth of foundation influence. This study i!.
based on the assumption that ~oils 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 conditionc;. In order to reveal the nature and extent of
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
HP KUMAR Project No. 16-7-477
,
Keith Novick
October 24, 2016
Page 3
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,
H-P KUMAR Project No 16·7·477