HomeMy WebLinkAboutObservation of Excavation 03.28.2024
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
March 28, 2024
Jason Spaulding
531 Country Road 260
Silt, Colorado 81652
Lspaulding81@gmail.com
Project No. 24-7-195
Subject: Observation of Excavation, Proposed Addition, 3125 County Road 241, New
Castle, Colorado
Gentlemen:
As requested, a representative of Kumar & Associates observed the excavation at the subject
site on March 19, 25, and 28, 2024 to evaluate the soils exposed for foundation support. The
findings of our observations and recommendations for the foundation support are presented in
this report. The services were performed in accordance with our agreement for professional
engineering services to Jason Spaulding dated March 13, 2023.
We understand the proposed addition has been designed to be founded on spread footings
bearing on the natural soils and sized for an assumed allowable bearing pressure of 1,500 psf
by the structural engineer, Censpace, LLC.
At the time of our visit to the site on March 19, 2024, the foundation excavation had been cut
in one level from 2 to 3 feet below the adjacent ground surface. The soils exposed in the bottom
of most of the excavation consisted of sandy to very sandy silt with scattered gravel. Results of
swell-consolidation testing performed on samples taken from the site, shown on Figure 1,
indicate the soils are compressible under conditions of loading and wetting and exhibit a
hydrocompression potential when wetted under a constant 1,000 psf surcharge. The
hydrocompression potential shown on Figure 1 is higher than typically exhibited by soils in
the area and could be due to the gravel content and sample disturbance during sampling. No
free water was encountered in the excavation and the soils were slightly moist to moist.
In the southeast corner of the foundation excavation, man-placed fill material was encountered.
This area was subexcavated about 4 feet deep where an abandoned concrete septic tank was
encountered. It was recommended that the tank be removed and the hole backfilled with
structural fill beneath the footing or the foundation be re-designed to span the area of existing
fill. It was decided to re-design the foundation to span the area fill around the tank.
At the time of our visit to the site on March 25, 2024, the fill material beneath the footing had
been removed down to the top of the abandoned septic tank (about 4 feet deep) or on the sides
Jason Spaulding
March 28, 2024
Page 2
Kumar & Associates, Inc. ® Project No. 24-7-195
of the tank, down to native material (about 8 feet deep). It was recommended to backfill up to
footing grade with 3-inch-minus base course material.
At the time of our visit to the site on March 28, 2024, the 3-inch-minus material had been placed
inside the tank and up to footing grade and appeared to be well compacted. The south footing is
planned to be extended about 3 feet to the east, outside of addition area, and to bear entirely on
native material. The south foundation wall has been designed to span the area of fill material
as shown on the revised foundation plan from Censpace, LLC, dated March 21, 2024.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, spread footings placed on the undisturbed natural soil designed for an allowable
soil bearing pressure of 1,500 psf can be used for support of the proposed addition. The exposed
soils tend to compress when wetted and there could be some post-construction settlement of the
foundation if the bearing soils become wet. Footings should be a minimum width of 16 inches
for continuous walls and 2 feet for columns. Loose and disturbed soils and existing fill in
footing areas should be removed and the bearing level extended down to the undisturbed natural
soils or reestablished with compacted structural fill. Exterior footings should be provided with
adequate soil cover above their bearing elevations for frost protection. 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 a lateral earth pressure based on an equivalent fluid unit weight of at least
55 pcf for on-site soil as backfill. Structural fill placed within floor slab areas can consist of the
on-site soils 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. Landscape that requires regular heavy
irrigation, such as sod, and sprinkler heads should not be located within 5 feet of the foundation.
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 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.
Kumar & Associates
