HomeMy WebLinkAboutSubsoil Studylftrtii¡r;;ifi'åifî:Étrfr'"nÊü**'
An Employcc Owncd Gompony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.com
Offrce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
July 12,2021
Gina & Dan Sikora
3342 Vfest Toneys Peak Drive
Superior, Colorado 80027
gl com
RECEMED
JAN 0 7 ;¿0l¿:-
..,îF,iÅfthg,*-,
Subject: Subsoil Study for Foundation Design, Proposed Residence, 88 Gossamer Road,
Lot 88, Filing 7,Elk Springs, Garfield County, Colorado
Dear Mr. Shaw:
As requested, Kumar and Associates 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 you dated May 10,2021. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
report.
Proposed Construction: \Me understand the proposed residence will be one to two-story wood
frame construction above a crawlspace or a slab-on-grade with an attached garage. Garage floor
will be slab-on-grade. The house will be located in the upper part of the building envelope. Cut
depths are expected to range between about 3 to 6 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 desuibed
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The lot was vacant at the time of our fïeld exploration. Vegetation consists of
sage brush, grass and weeds with scattered juniper trees. Overall, the ground surface in the
building envelope is moderately sloping down to the south at grades of about 10 to 15 percent.
There is a steeper slope of about 35 percent in the middle of the building envelope with basalt
boulders exposed on the ground surface. A dry drainage crosses the site below the building
envelope as shown on Figure l.
Subsurface Conditions: The subsurface conditions at the site were evaluated by observing two
exploratory pits at the approximate locations shown on Figure l. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about 6 inches of topsoil, consisted of
2 to 2Yz feet of basalt gravel, cobbles and boulders in a calcareous sand, silt and clay matrix
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down to the maximum depths explored of Zt/z and 3 feet at which point practical digging refusal
on basalt boulders with a mini-excavator was encountered. A gradation test was performed on a
disturbed sample of the silty sand and gravel matrix soils as presented on Figure 3. Testing
indicates the sample is moderately plastic. No free water was observed in the pits at the time of
excavation and the soils were slightly moist. We anticipate excavation below about 4 to 5 feet
will require chipping or blasting of basalt boulders.
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 soil or limited depth of structural fill designed for an allowable
soil bearing pressure of 2,000 psf for support of the proposed residence. Footings should be a
minimum width of 16 inches for continuous walls and2 feet for columns. Loose and disturbed
soils encountered at the foundation bearing level within the excavation should be removed and
the footing bearing level extended down to the undisturbed natural 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 10 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 50 pcf for the on-site soil as backfill.
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 free-draining gravel should be placed beneath garuge level slabs. This material should
consist of minus 2-inch aggregate with less than 50% passing the No. 4 sieve and less than2%o
passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of
imported %-inch road base gravel 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 area that local perched groundwater can develop during times of
Kumar & Assoclates, lnc. o Project No.21-7-424
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heavy precipìøtion or seasonal runoff. Frozen ground during spring runoff can create a perched
condition. We recommend below-grade constructiono such as retaining walls and crawlspace
areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system.
The drains should consist of drainpipe placed in the bottom of the wall backfrll surrounded above
the invert level with free-draining granular material. The drain should be placed at each level of
excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum l% to
a suitable gravity outlet. 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 l% feet deep.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
l) lnundation of the foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfïll 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 densþ in landscape areas.
Free-draining wall backfìll 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 12 inches in the fîrst 10 feet ìn unpaved areas and a minimum slope of
3 inches in the first 10 feet in pavement and walkway areas. A swale may be
needed uphill to direct surface runoff around the residence.
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 the building. Consideration should be given to the use of xeriscape to
limit potential wetting of soils below the foundation caused by irrigation.
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
Kumar & Associates, lnc. @ Projecf No. 2l-7-424
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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; 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. Vy'e 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 veriff that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations preselrted herein. 'We recommend on-site observation
of excavations and foundation bearing strata and testing of structural 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.
Respectfirlly Submittod,
Kumar & Associates, Inc.
ø/ø
Mark,Gayeski, E.I.T.
Reviewed by:
Daniel E. Hardin, P.
MGlkac
Attachments: Figure 1
Figure 2
Pits
-Lo Pits
Figure 3 - Gradation Test Results
Kumar & Associates, lnc.Project No. 21"7"424
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APPROXIMATE SCALE_FEET
21 -7 -424 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
PI T
69
1
12'
Ptl 2
EL. 6908'EL.
0 0
t-lrl
LJlr
I-l-o-
LÀJô
I WC=15.0
+4=37
-ZOQ=28
LL=42
Pl=16
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LEGEND
TOPSOIL; SANDY T0 VERY SANDY SILT AND CLAY, FIRM, BROWN, SLIGHTLY MO|ST,
ORGANICS.
BASALT GRAVEL, COBBLES AND BOULDERS IN A SILTY SAND AND GRAVEL MATRIX, DENSE
TO VERY DENSE, SLIGHTLY MOIST, PALE TAN" CALCAREOUS.
DISTURBED BULK SAMPLE.
t PRACTICAL DIGGING REFUSAL WITH A MINI EXCAVATOR.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI EXCAVATOR ON MAY .I
1 , 2021.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PIAN PROVIDED.
4, THE EXPLORATORY PIT LOCAÎIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY
TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIATS SHOWN ON ÏI{E EXPLORATORY PIl LOGS REPRESENT lHE
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);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTU O ¿ZZ);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140);
LL = LIQUID LIMIT (ASTM D 4518);
Pl = PLASTICITY INDEX (ASTM D 4318).
21 -7 -424 Kumar & Associates LOGS OF EXPLORATORY PITS Íig. 2
!
HYOROMETER ANALYSIS SIEVE ANALYSIS
n¡E REAOTXCS
Iul HRS 7 HRSú vlx I ß ltil aôvtN tcutN dlf,tvtN at
cufi sou^RE oPE¡{NGs
ttÀ, t/aá t ttt
-*t-, _.
I
-.''..t
SAND GRAVEL
¡
I
Ll t- . r-_.2 127 )
FINE MEDIUM COARSE FINE COARSE
ta
P
too
90
80
70
ô0
t0
10
t0
20
t0
0
o
to
26
30
40
60
ao
70
ðo
00
roo
!t
E
I
H
I lt
l
l I
.a2g
CLAY TO SILT COBBLES
GRAVEL 37 X SAND
LIQUID LIMIT 12
SAMPLE OFr Silty Sond ond Grovel
.10 %
PLASTICITY INOEX
SILT AND CLAV
16
2AX
FROM!Borlng2O2'-2,5'
Th$. hrl rctulli opply only to lha
romplar whloh Yara larhd. lho
l.allng râporl rhall nol ba ¡rÞrcducod,
cxcapl ln lull¡ vllhost fh! wrltl.n
opprovdl ol Kumor & Attoololc¡, lnç.
Sl.vr onolyalr larl¡no lr plrlomrd ln
occordonc. wilh ASTM D69lJ, ASTM 07928,
ASTM C136 ondlor ASTU 0ll¡10.
21 -7 -424 Kumar & Associates GRADATION TTST RESULTS Fig. 3