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May 8,2019
Cindy and Royal Stillman
580 JB Court
Glenwood Springs, Colorado 81601
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Subject
Project No.19-7-121
subsoil study for Foundation Design, Proposed Auxiliary Dwelling unit, 580 JB
Court, Garfield County, Colorado
Dear Mrs. and Mr. Stillman:
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 January 25,2019. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed auxiliary dwelling unit (ADU) will be a single story
structure located on the site roughly as shown on Figure 1. Ground floor will be slab-on-grade or
structural over crawlspace. Cut depths are expected to range between about 3 to 5 feet.
Foundation loadings for this type of construotion 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 site is vacant and has been cut and filled to create a relatively flat building
area. The natural terrain slopes down to the west at about 20Yø gradebelow the steep hillside to
the east. Canyon Creek is to the west. Maroon Formation spines and fins are present on the
hillside to the north and east of the site. The building area has been cleared of vegetation and the
surrounding area is vegetated by pinyons, junipers and brush.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits at the approximato locations shown on Figure l. The logs of the pits are
presented on Figure 2. The subsoils encountered consist of medium dense, silty sand and gravel
with scattered cobbles colluvium. In Pit 2, about 3 feet of loose, silty sand and gravel fill existed
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above the natural soils. No free waler 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 constructiolr, spread footings placed on the
undistulbed natural soil designed for an allowable soil bearing pressure of 1,500 psf can be used
for support of the proposed ADU with a settlement risk. The soils tend to compress after wetting
under load and there could be post-construction foundation settlement possibly around I to Z
inches depencling on the depth and extent of wetting. Footings should be a minimum width of 20
inches for continuous walls and 2 feet fcrr columns. Loose disturbed soils and existing fill
encountered at the foundation bearing level within the excavation should be removed. Tlie
exposed soils should then be moistened and compacted. Ilxterior footings should be pr.vicled
with adequate cover above their bearing elevations for frost protection. Placement of footings at
least 36 inches below the exteric¡r grade is typically used in this area. Continuous foundation
walls should be heavily reinforoed top and bottom to span local anomalies such as by assumìng
an unsupported length ol at least 12 feet. Foundation walls aoting as retaining structures should
be designed to resist a lateral earth pressr¡re based on an equivalent fluid unit weight of at least
50 pcf for the on-site soil as backfill.
Floor Slal¡s: The natural on-site soils, exclusive of undocumented fill, are suitable to support
lightly loaded slab-on-grade construction with accepted rjsk of settlement. All undocumentccl
fill under proposed slabs-on-grade should be removed and replaced wittr properly compacted fÌll
To reduce the effects of some differential movement, floor slabs should be separated from all
bearing walls and colulnns 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 s¡:acing and slab reínfurcement should be establishetf 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 for support. This
material should consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and
less than l2o/o passingthe No. 200 sieve.
All lill materials lbr support of floor slabs shoulcl be compacted to at least g1Ytt of maximum
standard Proctor density at a moisture content near optimurn. 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 locai perched groundwater can rievelop during times gf
heavy precipitation or seasonal runoflì Frozerr ground duriug spring runoff can create a perchecl
Kamar & Asçaciala*, lnc. :;
Frai*øtNx.1g-7"121
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condition. 'We recommend below-grade construction, such as retaining walls and basement
areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. An
underdrain should not be provided around shallow crawlspace areas to help limit potential
wetting of bearing soils from shallow wâter sources.
V/here provided, the drains shoulel consist of drainpipe placed in the bottom of the wall backfrll
surrounded above the invert level with free-draining granular material. The drain shoul{ be
placed at each level ofexcavation and at least I foot below lowest adjacent finish grade and
sloped at a minimum 7a/a to a suitable gravity outlet. Free-draining granular material used in the
underdrain systetn should contain less than 2% passing the No. 200 sieve, less than 50% passing
the No.4 sieve and have a maximum size af 2 inches. The drain gravel backfill should be at
least 1t1z feei deep.
Surface Drainage: Providing proper surface grading and drainage will be critical to lirniting
subsurface wetting and potential building distress. The following drainage precautions should be
observed during construction aad maintained at all times after the AÐU has been completed:
1) Inundation ofthe foundation excav¿tions and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optímum moisture and compacted to
at least 95a/o of tlte maximum standard Proctor density in pavement and slab areas
and to at least 90% of the maxirnum 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 pavement and walkwåy areås.
4) Roof downspouts ancl drains should discharge well beyond the iimits of a1l
backfill.
5) Landscaping which requires regular heavy irrigalion should be located at least 10
feet from the building.
Limltations: 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 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 concerned
llç¡nar & Aesacialet, lac" 1'Pr*Jeet Nc. 19"7"12"t
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about MOBC, then a professional in this special fîeld 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
oxcavation 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
should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendationso and to verifu 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.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kum;rr & Á,ssor:i¡rtes, lnc.
Shane J. Robat, P.E
Pruject Manago
Reviewed by:
Steven L.
SJR/kac
attaclunenls Figure of Exploratory Pits
Figure 2 -Logs of Exploratory Pits
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K*mar & &**aeiate*, lnr. t:Ptojert No. 19"7-121
30
APPROXIMATE SCALE*FEET
19*7-121 Kumar & Associates LOCATION OF EXPLORATORY PITS Flg. 1
R
0
PIT f F'T 2
I WC=21.5
J -2OOx27
10
LEGËND
FILL; slLrY, SAND ANo cRAvËl, SCÂTTERED coBBLEs, LoûsE To M[0tuM DENSE, SLIGHTLyMOIST, RË0.
SAND AND GRAVTL (SM*GM); stLTY, SCÀTTËRËD CO8BLTS, MEOTUM OENSE, SUöHTLY MO|ST,
RED.
DISTUREED BULK SAMPLË.
NOTES "
1, ÏH[ EXPLORATORY PITS WËÊË EXCÀVATEÐ WITH A BÂCKHOË ON FEBRUARY 22, 2A19.
2, THT ËXFLORATORY PITS WERE LTCÀTED BY THE CIIENI.
3. THE TLTVATIONS ÕË THE EXPLORATORY PITS WERE NOT MEASURED AND THË LO6S OF THE
EXPLORATORY PITS ARE PLOTTËD TO DEPTH.
4. THE EXPLORATORY PIl LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DIGREËIMPIIED BY THE METHOÞ USTD,
5. THE LINËS SETWEËN MATERIALS SHOWN ÔN IHE EXPLORATORY PIT LOGS REPRESENT THEAPPR0XIMAIË Ê0UNÞÂRIES BETWEEN MÂTËRlÀt TYPES AND THE TRANs¡TtoNs MAt Bt cRADUAL.
6' GROUND WATER WAS NOT ENCOUNTERED IN THT PITS AT THE TIME OF DIGCING. PITS WTREBÂCKFILLËD SUBSEQUENT TO SAMPLING.
7. LABORATORY TTST RESULTS:
Wc = WAÏËR C0NTFNT (%) (ASTM D 2216):
-2OOg P€RCËNTAGE PASSING NO, 2OO SIEVE (ASTM D 1 1 40)
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19-7 -1?1 Kumar & Associates LOGS OF IXPLORATORY PITS Fîs. 2