HomeMy WebLinkAboutSubsoil Study for Foundation of Designrcnfffi ['.ffiflr:fn[i3;'*"'
An Employcc Orncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fa"r: (970) 945-8454
email: kaglenwood@kumarusa.com
wlvw. kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
December 27,2023
RM Construction
Affn: Blake Piland
5030 County Road 154
Glenwood Springs, Colorado 81601
blake@bui ldwithrm.com
Project No.23-7-711
Subject: Subsoil Study for Foundation Design, Proposed Residence, 34 Mariposa,Lot
GV-8, Aspen Glen, Garfield County, Colorado
Dear Blake:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to RM Construction dated December 15,2023. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed residence will be a two story, wood frame structure over
a crawlspace or basement level located in the area of the pits as shown on Figure 1. Ground
floor will be structural over crawlspace or slab-on-grade. Cut depths are expected to range
between about 4 to 8 feet. Foundation loadings for this type of construction are assumed to be
relatively light and typical of the proposed type of construction.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The lot is currently vacant. The site slopes moderately down to the east at
grades of 5o/o to 15o/o. Vegetation consists of grass and weeds. Adjoining lots are developed
with single family houses.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about 1/z foot of topsoil, consist of
relatively dense, slightly silty sandy gravel with cobbles in Pit 2. About 7 feet of sandy silt was
encountered overlying the dense gravel soils at Pit 1. Results of a gradation analysis performed
sIt
N.
-N
on a sample of the sandy gravel (minus 3-inch SI te are
Figure 3. No free water was observed in the pits at the time of excavation and the soils were
slightly moist.
on
a
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed natural gravel soil designed for an allowable soil bearing pressure of
3,000 psf for support of the proposed residence. The sandy silt soils are lower density and will
\Omfe*rffmefWe recommend that the sand soils be removed from below the proposed
residence. Footings should be a minimum width of 16 inches for continuous walls and2 feet
for columns. Loose and disturbed soils and existing loose sand encountered at the foundation
bearing level within the excavation should be removed and the footing bearing level extended
down to the undisturbed natural gravel soils. Exterior footings should be provided with adequate
cover above their bearing elevations for frost protection. Placement of footings at least 36 inches
below the exterior grade is typically used in this area. Continuous foundation walls should be
reinforced top and bottom to span local anomalies such as by assuming an unsupported length of
at least l0 feet. Foundation walls acting as retaining structures should be designed to resist a
lateral earth pressure based on an equivalent fluid unit weight of at least 45 pcf for the on-site
soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly to
moderately 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 free-draining gravel should be placed beneath basement level
slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with less than
50% passing the No. 4 sieve and less than2o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95o/o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site 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 the arcathat local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoffcan 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 drains should consist pe ln
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 lYo to
Kumar & Associates, lnc. o Project No. 23-7-711
-3-
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yo passingthe 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 lYzfeet deep.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction. Drying could increase the expansion potential of the soils.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95%o of the maximum standard Proctor density in pavement and slab areas
and to at least 90%o of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be capped with about 2 feet of the on-site, finer
graded soils to reduce surface water infiltration.
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 6 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area atthis 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 pits excavated at the locations indicated on Figure 1
and to the depths shown on Figure 2, 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 concemed
about MOBC, then a professional in this special field of practice should be consulted. Our
findings include interpolation and extrapolation of the subsurface conditions identified at the
exploratory pits 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 at once so 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
monitor the implementation of our recommendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
Kumar & Associates, lnc. @ Project No. 23-7-711
-4-
or modifications to the recommendations presented herein. We recommend on-site observation
ofexcavations and foundationbearing strata and testing ofstructural fill by a representative of
the geotechnical engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates, lnc.
Daniel E. Hardin, P
Rev. by: SLP
DEH/kac
attachments Figure 1 - Location of Exploratory Pits
Figure 2-Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test Results
Figure 4 - Gradation Test Results
Table 1 - Summary of Laboratory Test Results
Kumar & Associates, lnc. o Project No. 23-7-71{
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Fig. 1LOCATION OF EXPLORATORY PITS23-7 -7 1 1 Kumar & Associates
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PIT 1
EL. 98.8'
PIT 2
EL. 92.3'
0 0
5
WC=6.7
DD=80
-200=59
IWC=1.7
+4=67
-200=5
5
WC=11.8
DD=96
10 10
TOPSOIL. ORGANIC SANDY SILT, FIRM, SLIGHTLY MOIST, DARK BROWN.
SILT (ML); SANDY, SCATTERED GRAVEL, STIFF' SLIGHTLY MOIST, REDDISH BROWN.
GRAVEL (GM); SANDY, SLIGHTLY SILTY, WITH COBBLES, DENSE' SLIGHTLY MoIST'
BROWN.
IK HAND DRIVEN LINER SAMPLE.
I
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II DISTURBED BULK SAMPLE.
Lr
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I enacrtclL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON DECEMBER 15,2025.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO
THE BENCHMARK ON FIG. 1.
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY
TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT %) (ASTM D 2216)t
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trJlL
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+4 = pERcENrAor niilir.rid-oli No.-+-'sreve lasrv D 422);
-200= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140).
Fig. 2LOGS OF EXPLORATORY PITS23-7-711 Kumar & Associates
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SAMPLE OF: Sondy Sili
FROM:Pii1('^4'
WC = 6.7 %, DD = 80 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
I
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llEuerotpyonyow
nmolcr trdrd. lh. LuE EFrt
.hol not b. EPFduc.d, .sPt ln
full. rfihout th. rrltLn oDpMl ot
l(umdr ond Lodot ., lE. Smll
Comndqtlon idung Frlomad h
dco.dec! rllh Asllt D-,15,1€.
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100- KSF t0.l.0I
Fig. 5SWELL-CONSOLIDATION TEST RESULTSKumar & Associates23-7 -7 1 1
SIEVE ANALYSISHYDROYETER ANALYSIS
CIIiIR SQUARE OPENITOS
ttt tf^. t t tr. t.
U.S. SIANDARD sERIEs
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OF
CljY TO SILT COBBLES
GRAVEL 67 X SAND 28 X
uQutD uMrT - Pl.AsTlclTY INDEX
SAMPLE OF: Sllghlly Sllty Sdndy Grov.l
SILT AND CI.AY 5 X
FROM: Plt 2O 1'-1.5'
GRAVELSAND
MEDIUM COARSE FINE COARSEFINE
romDlar whloh waru lql.d. Th.
hrllirg ruport ftall not b. nprcducrd,
lxo.Dl ln lull. wllhoul lhr udll n
qoorbvql of Kumor & A$illoht, lno.
Sirh qnqtnlr Ltllnq lt ilrtom.d ln
qccordonci vllh Asfrt Ddgls. AsTll D7928,
A5lll Ct36 ondlor A5Tll Dll4O.
Fig. 4GRADATION TEST RESULTSKumar & Associates23-7 -7 1 1
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and Engineers
Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.23-7-711
Sandy Silt
Sandy Silt
Slightly Silty Sandy Gravel
SOIL TYPE
losfl
UNCONFINED
COMPRESSIVE
STRENGTH
(o/ol
PLASTIC
INDEX
ATTERBERG LIMITS
LIQUID LIMTT
lolol
5
PERCENT
PASSING NO.
200 stEVE
59
28
SAND
(%)
67
GMDATION
(%)
GRAVEL
80
96
NATURAL
DRY
DENSITY
(pcfl
71
{%)
NATURAL
MOISTURE
CONTENT
6.74
.811
ATION
(ft)
DEPTH
6
4-4%2
SAMPLE LOI
BORING
1