HomeMy WebLinkAboutObservation of Excavation 11.12.25Geatechnica! and Materials Engineers Glenwood Springs, CO 81601
1(+AGeateKumar ni Associates, Inc 5020 County Road 154
and Environmental Scientists phone: (970) 945-7988
email: kaglenwood@kumarusa.com
www.kumarusa.com
An Employee Owned Company
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
November 12, 2025
Tate Civil
Attn: Tate Fairbanks
P.O. Box 2251
Glenwood Springs, Colorado 81602
tate{a)tateCiVil.c❑ni
- -
Project No. 23 7 124.A
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Subject: Observation of Excavation, Proposed Residence, 0960 County Road 107, Garfield
County, Colorado
Gentlemen:
As requested, a representative of Kumar & Associates, Inc. observed the excavation at the
subject site on November 11, 2025 to evaluate the soils exposed for foundation support. The
findings of our observations and recommendations for the foundation design are presented in this
report. We previously conducted a subsoil study for design of foundations at the site and
presented our findings in a report dated February 14, 2025, Project No. 23-7-124.
We understand that the proposed residence has been designed to be founded on spread footings
placed on the natural granular soils and sized for an allowable bearing pressure of 2,000 psf.
At the time of our visit to the site, the foundation excavation had been cut in one level from about
1 to 6 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation
consisted of very silty sand with scattered gravel. No free water was encountered in the
excavation and the soils were slightly moist to moist.
The soil conditions exposed in the excavation are consistent with those previously encountered
on the site and suitable for support of spread footings designed for the recommended allowable
bearing pressure of 2,000 psf. The subgrade had been compacted. Loose and disturbed soils
should be removed in the footing areas to expose the undisturbed natural soils. Other
recommendations presented in our previous report which are applicable should also be observed.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation excavation and the previous subsurface exploration at the site. Variations
in the subsurface conditions below the excavation could increase the risk of foundation
movement. We should be advised of any variations encountered in the excavation conditions for
possible changes to 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,
Kumar & Associates, ,s
.• ' • .ram
Daniel E. Hardin,
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Rev. by: RLD••
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K+AKumar &Associates, Inc.° Geolec
Geatechnical and Materials Engineers 5020 County Road 154
and Environmental Scientists Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood crkumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOPSED RESIDENCE
0960 COUNTY ROAD 107
GARFIELD COUNTY, COLORADO
PROJECT NO.23-7-124
FEBRUARY 14, 2023
PREPARED FOR:
BRITTANY MELONUK
0960 COUNTY ROAD 107
CARBONDALE, COLORADO 81623
b ritta nv la cer tena.e m a i 1. co m
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY........................................................................................ 1 -
PROPOSED CONSTRUCTION................................................................................................. 1 -
SITECONDITIONS ............................... I.................................................................................... 1 -
FIELDEXPLORATION............................................................................................................. 1
SUBSURFACE CONDITIONS.................................................................................................. 2-
DESIGN RECOMMENDATIONS............................................................................................. 2-
FOUNDATIONS..................................................................................................................... 2-
FLOORSLABS...................................................................................................................... 3 -
UNDERDRAWSYSTEM...................................................................................................... 3-
SURFACEDRAINAGE......................................................................................................... 4-
LIMITATIONS...................................................................................................... ................... 4-
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. 0 Project No. 23-7-124
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at
0960 County Road 107, Garfield County, Colorado. The project site is shown on Figure 1. The
purpose of the study was to develop recommendations for the foundation design. The study was
conducted in accordance with our agreement for geotechnical engineering services to Brittany
Melonuk dated January 19, 2023.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their classification and other engineering
characteristics. The results of the field exploration and laboratory testing were analyzed to
develop recommendations for foundation types, depths and allowable pressures for the proposed
building foundation. This report summarizes the data obtained during this study and presents our
conclusions, design recommendations and other geotechnical engineering considerations based
on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed residence will be a two- or three-story wood -framed structure with an attached
garage and partly cut below existing grade to flatten the site. Ground floor will be slab -on -grade.
Grading for the structure is assumed to be relatively minor with cut depths between about 2 to
6 feet. We assume relatively light foundation loadings, typical of the proposed type of
construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The project site is currently vacant. There is an existing residence to the west of the proposed
building area. Topography at the site is valley side with moderately sloping terrain down to the
south. Vegetation consists of native grass and weeds and pinon and juniper trees.
FIELD EXPLORATION
The field exploration for the project was conducted on February 2, 2023. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
The borings were advanced with 4-inch diameter continuous flight augers powered by a truck -
mounted CME-45B drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Kumar & Associates, Inc. ® Project No. 23-7-124
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Samples of the subsoils were taken with 1% inch and 2 inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30
inches. This testis similar to the standard penetration test described by ASTM Method D-1586.
The penetration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
Beneath about % to 1 foot of topsoil, the subsoils mainly consist of relatively dense, gravel and
cobbles with probable boulders in a sandy silt matrix material down to the maximum depth
explored of 16 feet. About 3% feet of silty sand with gravel was encountered above the gravel
and cobbles in Boring 1.
Laboratory testing performed on samples obtained from the borings included natural moisture
content, Atterberg limits, and gradation analyses. Results of gradation analyses performed on
small diameter drive samples (minus 11/z-inch fraction) of the coarse granular subsoils are shown
on Figure 4. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 2,000 psf. Based on experience, we expect
initial settlement of footings designed and constructed as discussed in this section
will be about 1 inch or less. There could be potential for post -construction
differential settlement of around 1 inch if the bearing soils are wetted.
2) The footings should have a minimum width of 18 inches for continuous walls and
2 feet for isolated pads.
Kumar & Associates, Inc. 0 Project No. 23-7-124
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3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
4) Continuous foundation walls should be 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 corresponding to an equivalent fluid unit weight of at least
50 pcf for the onsite soils as backfill excluding organics and rock larger than
6 inches.
5) The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the relatively dense natural granular soils. The
exposed soils in footing area should then be moistened and compacted.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on -site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade
construction. To reduce the effects of some differential movement, floor slabs should be
separated from all bearing walls and columns with expansion joints which allow unrestrained
vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage
cracking. The requirements for joint spacing and slab reinforcement should be established by the
designer based on experience and the intended slab use. A minimum 4-inch layer of relatively
well graded sand and gravel, such as road base, should be placed beneath slabs -on -grade for
support. This material should consist of minus 2-inch aggregate with at least 50% retained on
the No. 4 sieve and less than 12% passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95% of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
on -site granular soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
mountainous areas that local perched groundwater can develop during times of heavy
precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched
condition. We recommend below -grade construction, such as retaining walls, crawlspace and
basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain
system. The proposed slab -at -grade construction should not need a perimeter underdrain.
Kumar & Associates, Inc. 0 Project No. 23-7-124
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If below grade construction is proposed, the drains should consist of rigid perforated PVC
drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free -
draining granular material. The drain should be placed at each level of excavation and at least 1
foot below lowest adjacent finish grade and sloped at a minimum 1 % to a suitable gravity outlet
or sump and pump. Free -draining granular material used in the underdrain system should
contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least 1 Meet deep and covered
with filter fabric such as Mirafi 140N or 160N.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
1) Inundation of the foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95% of the maximum standard Proctor density in pavement and slab areas
and to at least 90% of the maximum standard Proctor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum
slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas. Free -draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on -site soils to
reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least
5 feet from foundation walls.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area at this time. We make no warranty either express or implied.
The conclusions and recommendations submitted in this report are based upon the data obtained
from the exploratory borings drilled at the locations indicated on Figure 1, the proposed type of
construction and our experience in the area. 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
Kumar & Associates, Inc. ® Project No. 23.7-124
-5-
practice should be consulted. Our findings include interpolation and extrapolation of the
subsurface conditions identified at the exploratory borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
during construction appear different from those described in this report, we should be notified so
that re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for design purposes. We are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented herein. We recommend on -site observation
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectful)
Kumar &
Robert L. I
Reviewed 1
Steven L. Pawlak, P.E.
RLD/kac
Kumar & Associates, Inc. I" Project No. 23-7.124
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�0 COUNTY ROAD 107COUNTY ROAD 107
50 O 50 100
APPROXIMATE SCALE —FEET
23-7-124 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
o. ie.a ru.. M_7_4nA
SAMPLE
LOCATION
NATURAL
MOISTURE
CONTENT
%
NATURAL
DRY
DENSITY
GRADATION
PERCENT
PASSING E
200 SIEVE
_ ATTERQERG
LIQUID LIMIT
%
LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
s
SOIL TYPE
BORING
DEPTH
91)
GRAVEL
NO
SAND
N
PLASTIC
INDEX
%
1
1
19.3
Very Silty Sand
2%
47
Very Silty Sand
2
3
9.3
23
36
41
Very Silty Sand with
Gravel
10
12.4
10
45
45
51
17
Very Silty Sand with
Gravel
BORING 1
BORING 2
L o
0
50/3
a : 81 /12
WC=19.3
15/6, 50/6
—200=47
g6/12
WC=9.3
5
+4=23
5
50/12
—200=41
49/ 12
w
L-
w
UJ
10
73/12
30/12
10
WC=12.4
— a_
+4=10
—200=45
LL=51
PI=17
15 �~
50/2
50/12
15
20
20
S
3
8
Ea
r`
k "g.
rP
23-7-124
Kumar & Associates
LOGS OF EXPLORATORY
BORINGS
Fig. 2
o-
LEGEND_
® TOPSOIL; CLAY AND SILT, SANDY, FIRM, MOIST, BROWN, ORGANIC, FROZEN.
SAND (SM); VERY SILTY, WITH GRAVEL AND SCATTERED COBBLES, MEDIUM DENSE
MOIST, TAN, SLIGHTLY CALCAREOUS.
GRAVEL AND COBBLES (GM); POSSIBLE BOULDERS, SANDY SILT MATRIX, MEDIUM
DENSE, SLIGHTLY MOIST, TAN, CALCAREOUS, BASALT FRAGMENTS.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8-INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
SLIGHTLY
DENSE TO
50/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 50 BLOWS OF A 140-POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
►[OW
1. THE EXPLORATORY BORINGS WERE DRILLED ON FEBRUARY 2, 2023 WITH A 4-INCH-DIAMETER
CONTINUOUS -FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF
THE EXPLORATORY BORINGS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE
DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
-200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140);
ILL = LIQUID LIMIT (ASTM D4318);
PI = PLASTICITY INDEX (ASTM D4318).
23-7-124 1 Kumar & Associates I LEGEND AND NOTES I Fig. 3