HomeMy WebLinkAboutSubsoil Study for Foundation Design 08.02.2021I(.+tt*tr*[ffifffiilÍå**
An Em$oycc Ovrncd Compony
5û2ûCoua$Road I54
Glenr¡,ood Springs* CO 81601
phone: (97û) 945-7988
fàx (970) 9¿t5-8454
email ka glørwood@Íunanua.corn
www.kurnarusa.coru
OÍñce LocatiolÌs: Ðmver (HQ! kúer- C¡rlorado Springs! Fort Collins Glørrd Springs and Su¡nilit Cor¡nty. Colorsdo
August 2,202I
Jack Panter
100 Wildwood Lane
Glenwood Springs, Colorado 81601
omteriack(ò.msn.com
Project No. 21-7-554
Subject: Subsoil Study for Foundation Design, Proposed Addition, 100 Wildwood Lane,
Glenwood Springs, Colorado
Gentlemen:
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 Jack Panter dated June 22,2021. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed addition will be located on the south side of the existing
residence generally in the location of our exploratory pits shown on Figure 1. Ground floor will
be slab-on-grade or structural over crawlspace. Cut depths are expected to range between about
2 to 4 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: There is an existing two-story wood-framed single-family residence at the
subject site. The existing residence is founded on 16-inch wide spread footings bearing on the
natural granular soils. The terrain at the site is valley bottom topography with gently to
moderately sloping ground down to the south. Elevation difference across the proposed addition
is about I to 3 feet. Vegetation at the site consists of landscaped lawn, trees, and flower beds.
The Colorado River is about 200 feet to the south-southwest of the area of the proposed addition.
There is a minor depth of previously placed fill material at the westem side of the proposed
addition from the construction of the existing residence.
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
a
presented on Figure 2. The subsoils encountered, below about I foot of topsoil, consist of
slightly silty sandy gravel with cobbles and boulders. Results of a gradation analysis performed
on a sample of sandy gravel (minus 5-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 addition. Footings shoul be a minimum width l6
J-"ffiñ.ù'allsand2feetforcolumns.Looseanddisturbedsoilsandexistingfill
encountered at the foundation bearing level within the excavation should be removed and the
footing bearing level extended down to the undisturbed natural granular 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 (if any) should be designed to resist alateral earth pressure based on an equivalent
fluid unit weight of at least 45 pcf for the on-site gravel 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
rcducc damagc duc to shrinkagc cracking. Thc rcquircmcnts for joint spacing and slab
reinforcement should be established by the designer based on experience and the intended slab
use.
All fiIl materials for support of floor slabs should be compacted to at least 95Yo of maxrmum
standard Proclor clensity at a moisture content near optimum. Requirecl fill can consist of the on-
site soils devoid of vegetation, topsoil and oversizecl (plus 6-inch) rock.
Underdrain System: A foundation underdrain should not be required in areas at existing grade
or shallow crawlspace areas of less than 4 feet if foundation wall backfill is adequately
compacted and surface drainage precautions are taken.
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
Kumar & Asssciateq lnc. è Project No. 2f.7-554
-3 -
seasonal runoff. Frozen ground during spring runoffcan create aperched condition. We
recommend below-grade construction, such as retaining walls and deeper crawlspace areas, be
protected from wetting and hydrostatic pressure buildup by an underdrain system.
The drains (if any) should consist of 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 ofexcavation and at least I foot below lowest adjacent finish grade and
sloped at a minimumYzYoto a suitable gravity outlet. Free-draining granular material used in the
underdrain system should contain less than ZYopassing 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
leastl/z feet deep and covered with filter fabric such as Mirafi l40N or 160N.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the addition 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%oof 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 capped with about 2feet 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 first l0 feet in unpaved areas and a minimum slope of
3 inches in the first t0 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 at this time. \üe make no warrarity 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, 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 practice should be consulted. Our
Kumar & Àosociateg trnc. o Pmject No. 21:7-554
4
findings include interpolation and extrapolation of the subsurface condilions identified at the
exploratory pits and variations in the subsurface conditions may not become evident until
excavation is pert-ormed. lf conditions encountered during construction appear different from
those described in this report, we should be notified at once so re-evaluation of the
recommendations rnay be made.
This reporthas beenprepared forthe exclusive use by ourclient for designpurposes. Vy'e are not
responsible for technical interpretations by others of our information. As the project evolveso 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 sÍata 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
Respectfu lly Submitted,
Kumnr & Ass¡lciates, lrrc.
Robert L. Duran, P
Reviewed by:
Daniel E. Hardin, P.E.
RLD/kac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 * Gradation Test Results
cc Kurtz Engineering - Brian Kurtz (krUtæg:¡Cç{C¿Iajfq{)$lff )
rlqp
Kumar & Associates, lnc, :Project No. 21-7-554
40
APPROXIMATE SCALE-FEET
21 -7 -5s4 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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PIT 1
EL. 1 01'
PIT 2
EL. 1 00'
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I WC=4.3
-.i +4=55
-200=8
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LEGEND
TOPSOIL; SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN, ORGANIC.
GRAVEL (GM-SM); SANDY TO VERY SANDY, SILTY, WITH COBBLES AND BOULDERS, DENSE TO
VERY DENSE, SLIGHTLY MOIST, BROWN, SUB_ROUNDED ROCK.
Ii
I
DISTURBED BULK SAMPLE-
PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JULY 2A, 2021
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLÄN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO
THE CONCRETE SLAB AT SOUTHEAST CORNER OF EXISTING RESIDENCE WITH A EL. 1OO"
ASSUMED.
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY
TO THE DEGREE IMPLIED BY THE METI-IOD 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, LABORAÏORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM O ZZIA);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTV O +ZZ);
-2AA= PERCENTAGE PASSING No. 200 SIEVE (ASTM D 1 140).
21 -7 -554 Kumar & Associates LOGS OF EXPLORATORY PITS Frg. 2
s*
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HYDROMETER ANALYSIS SIEVE ANALYSIS
U.S. SANDARö SERIS CLEÂR SOUARE OPENINGS
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IIME READINCS
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LLIMETERS
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DIAMETER OF PARTICLES IN MI
CLAY TO SILT COBBLES
CRAVEL 55 %
LIQUID LIMIT
SAMPLE OF: Pi+ 2 O 4'-5
SAND 37 %
PLASÏICITY INDEX
SILT AND CLAY 8 %
FROM: Slighlly Silty Sondy Grovel wilh Cobbles
Thasc losl.€sulls opply only lo thr
somÞl.s which w.r. laslcd, Th.
tr3lliìg raport sholl nol br rcproduc.d,
excepl ln full, vllhoul lh6 wrltlon
opprovol ol Kumor & AsÊoclol..!, lnc.
si6vê onolysis fu9llng is p.rformad ¡n
qccordoncê wllh ASTM 069f3, ASTM D7928,
ASTM C136 ond/or ASTM D1140.
GRAVELSAND
MEDIUM COARSE FIN E COARSEFIN E
21 -7 -554 Kumar & Associates GRADATION TEST RESULTS Fig. 3