HomeMy WebLinkAboutSubsoils Report for Foundation DesignlGrtU***Ugi111*"-"
An Employcc olmcd Compony
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 ([IQ), Pake4 Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
October 27,2021
Jim Frayn
13A Emerson Street
Mount Prospect, Illinois 60056
jfrayn@manhard.com
Project No. 21-7-768
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 42, Filing 9,
Elk Springs, 3030 Elk Springs Drive, Garfield County, Colorado
Dear Jim:
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 you dated September 20, 2021. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: Plans for the proposed residence were conceptual at the time of our
study. The proposed residence is assumed to be a one or two-story wood-frame strucfure
possibly over a lower walkout basement level with attached garage located on the site within the
building envelope shown on Figure l. Ground floors could be sttuctural over crawlspace or slab-
on-grade. Cut depths are expected to range between about 2 to 5 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 subject site was vacant at the time of our field exploration. The ground
surface was sloping down to the south at an estimated grade of I perceqlVegetation consists of
grass and sagebrush with scattered juniper trees. Scattered basalt cobbles and boulders were
visible at the surface.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three 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 1to lVz feet of topsoil, consist of
dense, basalt cobbles and boulders in a highly calcareous sandy silt matrix (caliche) down to the
-2-
maximum explored depth of 3% feet. Results of a gradation analysis performed on a sample of
basalt gravel and caliche matrix (minus 3-inch fraction) obtained from the site are presented on
Figure 3. No free water was observed in the pits at the time of excavation and the soils were
slightly moist.
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 granular soil designed for an allowable soil bearing pressure of
.
2,500 psf for support of the proposed residence. The fine-grained matrix soils generally tend to
compress after wetting and there could be up to around I inch of post-construction foundation
settlement. Footings should be a minimum width of lt5 inches for continuous walls and 2 feet for
columns. Topsoil and loose 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. We should observe the completed foundation excavation for bearing
conditions. Exterior footings should be provided with adequate cover above their bearing
elevations for frost protection. Placement of footings at leas!1@hes-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 12 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.
Basalt boulders and hard matrix materials were encountered in the exploratory pits and may be
difficult to remove during foundation excavation. Rock excavation techniques such as a
hydraulic hammer or equipment of sufficient size may be required to complete foundation
excavations,
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 minirnum 4-inch
layer of free-draining gravel should be placed beneath basement level slabs to facilitate drainage.
This material should consist of minus Z-inch aggregate with less than 50% passing the No. 4
sieve and less than 2o/o passingthe No. 200 sieve.
Kumar & Attoclatet, lnc. @ Project No. 21-7-768
-J-
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 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 area 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 (if any), 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 backfill sunounded 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%oto
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 I % feet deep.
Surface Drainage: The following drainage precautions should be observed during construction
and rnaintained at all times after the residence has been completed:
1) Inundation ofthe 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 95To 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.
Free-draining wall backfill should be covered with filter fabric and capped with
about 2 feet of the on-site, finer graded soils to reduce surface water infiltration.
3) The ground surface sunounding 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. 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.
Kumar E Associates, lnc. @ Projcct No. 21-7-768
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 I
and to the depths shown on Figure 2, theproposed t1rye of construction, and our experience in
the area. Our services do not include determining the presence, prwention 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. Our
findings inclirde interpolation and exfrapolation 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 conskuction appear different from
those described in this report, we should be notified at once so re-evbluation 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 modifioations to the recommendations presented herein. We recommend on-site observation
of excavations and foundation bearing skata and testing of structural fill by a representative of
the geotechnical engineer.
If you have any questions or if we may be of firrther assistance, please let us know.
Respectfully Submiued,
Kumar & Associates, Inc.W T. ?otrtnaf
James H. Parsons, P.E.
Reviewed by:
Steven L. Pawlak,
JHP/kac
attachments Pits
-4-
Pits
Test Results
Figure
Figure 3-
Table I - Summary of Laboratory Test Results
o 15222
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Kumar & Associaler, lnc. 6 Project No. 21-7-788
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APPROXIMATE SCALE_FEET
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21 -7 -768 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
I
PIT 1 PIT 2 PIT 3
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0
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I WC= 19.9
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LEGEND
N TOPSOIK SILT, SANDY, ORGANICS, FIRM, SLIGHTLY MOIST, BROWN
COBBLES AND BOULDERS (GM-ML); BASALT ROCK, HIGHLY CALCAREOUS ANDY SILT MATRTX
(cALtcHE), DENSE, SLIGHTLY Motsr, eALE 6RAy.
t DISTURBED BULK SAMPLE.
t PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI EXCAVATOR ON OCTOBER 22. 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 NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATIONS 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);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D
D
11
422)
40).
21 -7 -768 Kumar & Associates LOGS OF TXPLORATORY PITS Fig. 2
a
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50
80
70
lo
90
ldr
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E
-12!'OF PARTICLES IN M
52
CLAY TO SILT COBBLES
GRAVEL 39 X SANO
LIOUID LII'IT
SAMPLG 0F; Sllty Sond ond Grdv.l
12:{
PTASTICITY INDEX
SILT AND CLAY 19 %
FROM:Plt1O2-3.5'
Tha$ lcd @ulls opply only to lh.
Bomplls whlch w.ro l.rl.d. ThelAllng ropori 3holl nol b. roproducrd,
.xo.pl ln full, wlthoul lh. wrlllcnqpprovol ol Kumqr & Alsociol.r, lnc.
Shva onoltll! t!3llng l! prrtomad ln
occordon€ wlth ASTTJ D69lt, ASTM 07926,
ASTM Ct36 ondlor ASIM Dll40.
HYOROMETER ANALYSIS SIEYE ANALYSIS
2,4 HRs 7 HnS
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anulr tautr lo Itm
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CL.EAR SOlJAi€ OPENIHGS
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SAND GRAVEL
FINE MEDIUM FINE COARSE
21 *7 -768 Kumar & Associates GRADATION TEST RESULTS Fig. 3
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPT LocATrdr,t GR!tlON AT LIMITS
PIT
tftt
DEPTH
t%l
I{ATURAL
IIOISIURE
coilIEl'tT
NATUhAL
DRY
DENSITY
locll
GRAI/EL
t%l
SAt{D
ftt
PERCEiTT
PASSII'|G NO.
200 sElrE
IIQUID TIMIT
l%l
PLASNC
r,lDE(
l%l 16rll
uilcor{trl,rED
colrpREsstvE
STR$reIH SOLTYPE
I 2lo 3Yz 19.9 39 42 19 Calcareous Sandy Silt and
Gravel