HomeMy WebLinkAboutObservation of Excavation 03.17.2020lGrI ,ffiå'*"5020 County Road 154
Glenwood Springs, CO 8f 601
phone:
fax:
945-7988
945-8454
email:marusa.com
www.kumarusa.comAn Employcc ûrncd Compony
ûffice Locations: Denver (HQ), Parke¡ Colo¡ado Springs, Fort Coliins, Glenwood Springs, and Summit County, Colorado
March 17,2020
Jonah Frank
6023 County Road 214
New Castle, Colorado 81647
jonah@sopris.net
Project No. 20-7-l l 1
Subject: Observation of Excavation, Proposed Barn, 6023 County Road 214 (PeachValley
Road), Garfield County, Colorado
Dear Jonah:
As requested, a representative of Kumar & Associates observed the excavation at the subject site
on February 27,2020 to evaluate the materials exposed for foundation support. 'We subsequently
performed compaction testing on structural fill placed below footing areas of the building. The
findings of our observations, test results and recommendations are presented in this report. The
services were performed in general accordance with our agreement for professional engineering
services to you dated January 16,2020.
The barn will be a single-story, steel frame and metal structure with a slab-on-grade floor. The
building will partially retain the hillside. The structure has been designed to be supported on
spread footings assuming an allowable bearing pressure of 3,000 psf by the structural engineer.
At the time of our February 27 site visit, the foundation excavation was nearly complete and had
been cut in two levels from about 2 to 7 feet below the adjacent ground surface. The soils
exposed in the bottom of the completed portion of the foundation excavation areas consisted of
hard, sandstone bedrock. The east wall line footing excavation was not complete at this time.
During our visit, we were advised by the client that the remainder of the foundation excavation
would be dug down to bedrock and any areas sub-excavated below design footing bearing
elevation would be re-established with compacted base course. No groundwater was
encountered in the excavation and the bedrock was slightly moist.
We returned to the site on March 13 and performed compaction testing on the surface of the up
to about 2 feet depth of %-inch (CDOT Class 6) aggregate base course placed as structural fill
below footing areas in the southeastem portion of the excavation. The testing indicated
compaction of about rcA% standard Proctor density at a moisture content slightiy dry of
optimum using an assumed laboratory Proctor value based on our experience with the material.
Considering the conditions exposed in the excavation, the limited compaction testing and the
nature ofthe proposed construction, spread footings placed on the undisturbed bedrock and
compacted structural fill designed for an allowable bearing pressure of 3,000 psf can be used for
support of the proposed building. There could be some settlement due to the variable bearing
conditions but we do not expect the settlement to be excessive. Prior to the footing construction,
all loose disturbed material should be removed or re-compacted as needed. Footings should be a
minimum width of 16 inches for continuous walls and2 feet for columns. Exterior footings
should be provided with adequate soil cover above their bearing elevations for frost protection.
Jonah Frank
March 17,2020
Page2
Continuous foundation walls should be reinforced top and bottom to span local anomalies such
as by assuming an unsupported length of at least 10 feet. Foundation walls acting as retaining
structures should also be designed to resist alateral earth pressure based on an equivalent fluid
unit weight of at least 50 pcf for on-site soil and well broken bedrock (minus 6-inch size) as
backfill.
A perimeter foundation drain, consisting of 4-inch diameter PVC drain-pipe placed at least I foot
below lowest adjacent interior finish grade and sloped at a minimum Yzo/o to a suitable gravity
outlet should be provided. The drain gravel backfill should be at least lYz feet deep and covered
by filter fabric such as Mirafi 140N. As part of the drain system, at least 4 inches of free-
draining gravel should be provided immediatelybelow the floor slab. Free-draining granular
material used in the drain system should c¡ntain less than 2% passing the No. 200 sieve, less
than S}%passing the No. 4 sieve and have a maximum size of 2 inches. Minus %-inchscreened
rock is acceptable as the drain gravel.
Structural fill placed within floor slab areas can consist of the on-site soils and well broken
bedrock (minis -inch size), or a zuitable imported granular material such as base course,
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 90o/o SPD and the surface
graded to prevent ponding within at least 10 feet of the building. This may require a swale along
the uphill side.
The recommendations submitted in this letter are based on our observation of the materials
exposed within the foundation excavation and do not include subsurface exploration to evaluate
the subsurface conditions within the loaded depth of foundation influence. 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 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,
Ku¡nar &Inc.
David A.
DAY/kac
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Kumar & Associates, lnc. o Project No.20-7-111