HomeMy WebLinkAboutSubsoil Study for Foundation Design 04.16.18ÇoiVl F"Æ,tfnvt
H.PVKUMAR
Geotechnlcal Engineerlng I Englneering Geology
Malerials Teslng I Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax (970) 945-84i,4
Êmail: hpkglenwood@kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
April 16,2018 RECEIVED
Ch¡isJanusz JUN ÛE 2018
3644Kighway 82 6ARF¡ELD COUNTY
Glenwood Springs, Colorado coMMUNtTY DEVELSPMEN1
Cryjanugz I 23 @ gmail.con
Project No. 18-7-240
Srrhienf 'Subsoil Study for Foundaticn Ðesign, Proposed Residence, l,Ðt2, Janusz
Exemption Plat,3644 Highway 82, Garfield County, Colorado
Dear Mr. Janusz:
As requested, H-PYKumar performed a subsoil study for design of faundations at the subject site.
The stuclSr \r¡as conducted in accordance with our agreement for geotechnical engineering
services to Chris Janusz dated April 3, 2018. The data obtained and our recommendations based
on the proposed construction and subsurface conditions encountered are presented in this report.
A geologic hazards assessment of the subject site is beyond the scope of this report.
Fnoposed ConstructËo¡r: An existing mobile home on the lot will be removed and a new
residence constructed. The proposed residence will be a modular home over a garden level
basement located on the site as shown on Figure 1. Ground floors will be slab-on-grade. Cut
depths are expected to range between about 4 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 described
above, we should be notified to re-evaluate the recommendations presented ín this report.
Site Conditions: There are cun'ently multiple sheds and a mobile home on the lot. The building
site is relatively flat with the terrain sharply steepening further to the east down to the driveway.
There is minor grading including cut and fill leveling of the proposed building site. Vegetation
consists of grass, sagebrush, scrub oak, and scattered conifers with landscape.
a)
Subsurface Conditions: Thc subsurface conditions at the site were evaluated by excavating two
exploratory pits at the approximate locations shown on Figure 1. The pits were dug hy the. client
prior to our amival on the site. The logs of the pits are presented on Figure 2. The subsoils
encountercd,below about 1 foot of topsoil, consist of silty sand and gravel with cobbles and
boulders that extended down to the pit depths of 7Vz and SVzfeet. Around 1 foot of older man-
placed fill was encountered in Pit 2 below the topsoil. Results of gradation analyses perfo''ed
on $amples of silty sand and gravel (minus 3-inch fraction) obtained from the site are presented
on Figure 3. The laboratory testing is summarized in Table 1. No free water was observed in the
pits at the time of excavation and the soils were slightly moist.
Foundation Recommendatior¡s; Considering the subsoil conditions encountered in t¡e
exploratory pits and the nature of the proposed construction, we believe spread footings placed
on the undisturbed natural soil designed for an aliowable bearing pressure of 1,500 psf can be
used for support of the proposed residence with a risk of settlement. The risk of settlement is if
the bearing soils were to become wetted and precautions should be taken to prevent wetting.
Footings should be a minimum width of 18 inches for continuous walls and,Z feetfor columns.
All topsoil, existing fill, and all loose disturbed soils encountered at the foundation bearing level
within the excavation should be removed and thc footing bearing level extended down to the
undisturhed nattlral soils. The subgrade shouid then be moistened and compacted. 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 nsed in
this area' Continuous foundation walls should be well 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 also 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, excluding debris, topsoil and
oversized (plus 6 inch) rocks, as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to snpport lightly loaded
slab-on-grade construction. There could be some slab settlement if the subgrade becomes
wetted. To redtlce the cffects of some differential movemcnt, floor slabs should be separated
H.PÙKUMAR
Projec{ No. 18-7-240
-J-
from all bearing wails and columns with expansion joints which allow unrestrained vertical
movement. Floor slab control joints should be usecl to reduce damage due ts shrinkage crackjng.
The requirements for joint spacing ancl slab reinforcement should be established by the designer
based on experience and the intended slab use.
All fill materials for support of floor slabs should be compacted to at \east 95Vo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid ofdebris, topsoil and oversized rocks (plus 6-inch size).
Unelerdrain Systerm: A,lthough free water \ryas 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. Frozsn ground during spring runoff can also creâte a
perched eondition. We recommend below-grade construction, such as retaining walls and
basement areas, be protected from wetting and hydrostatic prcssure 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 1 foot below lowest adjacent finish grade and sloped at a minimum I7o to
a suitabie gravity outlet. If rigid PVC drain pipe is used, which we recommend, a pipe slope of
YzVo can be used. F¡ee-draining granular material used in the underdrain system should contain
less than 2Vo passing the No. 200 sieve, less than 507ø passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least lYz feet deep and be
covered by filter fabric. An impervious memb¡ane such as 20 or 30 mil PVC should be placed
beneath the drain gravei in a trough shape and attached to the foundation wall with mastic to
prevent wetting of the bearing soils.
Surface Drainage: Positive surface drainage is a very important aspect of the project to prevent
wetting of the bearing soils. The following drainage precautions should be observed during
construction and maintained at all times after the residence/ADU have been completed:
H-P\KUfvIAR
ProJect No. 18-7-240
-4
1) Inundatiott af the foundation excavations and unclerslab a¡eas should be avoiclecl
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least g1%o of the maximum standard Proctor density in pavement and slab areas
and to at least 90Vo of the maximum standard Proctor density in landscape areas.
Free-dlaining wall backfill should be capped with filter fabric and about 2 feet of
the on-site, finer graded soils to reduce surface water infiltration.
3) The ground surface surounding the exterior of the building should be sloped to
drain away from the foundation in all directions. S/e 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 walkway areas. A swale will likely be
needed uphill to direct surface runoff a¡ound the residence and ADU.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy imigation should be located at least 10
feet from the building. Consideration should be given to the use of xeriscape to
limit potential wetting of soils below the foundation caused by inigation.
Limitations: This study has been conducted in accordance with generally accepted gsotechnical
engineering principles and practices in this area at this time. We make no wananty either
express or implied. The conclusions and recommendations submitied 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 seruices 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
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 notifïed at once so re-evaluation of the
recommendations may be made.
H-PIEKUÍVAR
Projecl No. 18-7-240
5
This reporl has been prepared for the exclusive use by our client for design pulposes. 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 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,
FI-P* KUMAR
Robert L. Duran, E. I.
Reviewed by:
David A. Young, P.E.
RLDlkac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Gradation Test Results
Table 1 - Summary of Laboratory Test Results
cc: Kurtz & Associates * Brian Kurtz (kurtzengineer@yahoo.col!)
H-PryICIMAR Projecl No. 18-7-240
RESIDEN
PRO
PIT 1
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LOT 2
3644 HIGHWAY 82
LOT 1
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APPROXIMATE SCALE
1B-7-240 H-P *KUMAR
!rn iLiìnðr,¡r.j i ¡:r:ti¡ìseiùrî :jislice..LOCATION OF EXPLORATORY PITS Figure 1
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LEQEND
TQpsotl; sAND AND SILT, SCATTERED GRAVEL, SLIGHTLY MOIST, DARK REÐDISH BROWN,
SLIGHTLY ORGANIC.
FILL; SAND AND GRAVEL, SILIY, SL|GHTLY MOIST' REDDISH-BROWN
5AND AND GRAVËL (GM*SM); SILTY, SCATTËRED ÖOBBLËS ANÐ BOULDIRS, MEDIUM DENSE,
SLIGHTLY MOIsT, REOOISH_BROWN.
I DISTURBED BULK SAMPLE.
NCITES
1. lHE EXPLORÀTORY PITS WERE EXCAVATED WITH A BACKHOE ON APRIL 2, 2418.
2, THE LOCATIONS OF THE EXPLCIRATORY PITS WERE MEASURED APPROXIMATELY BY PACIN€ FROM
TEATURES SHOWN ON THE SITE PLAN PROVIDED'
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND ÏHE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
4, THË 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
APPROXIMÂTE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE ORADUAL
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF DRILLING. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D a22)l
-2AQ = PERCENTAGE PASSING NO' 200 SIEVE (ASTM D 1 1 40).
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18-7 -240 I{.PVKUMAR LOGS OF IXPLORATORY PITS Fig. 2
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HYOROMEÌER ANALYSIS SISVE ANALYSIS
lryE RADTNCS
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u.s. sÎ^NoAio sERtÊs CIIAR SOUARE OPININOS
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SAND GRAVÈL
FINE MEDIUM COARSE FINE COARSE
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DIAMETER OT PARTICLES
CLAY TO SILT COBBLES
SRAVEL 26 % SAND
LIQUID LIMIT
SAMPLT OF: Sllly Sond nllh Grovel
38%
PLÁSTICITY INDEX
SILT AND CLAY 36 %
FR0M:Plt1@6.5'-7.5'
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ROF IN MI
CLAY TO SILT COBBLES
GRAYEL 29 % SAND
LIQUID LI}iiIT
SAMPLE OF: Siliy Scnd lv¡lh Grav€l
59 X SItl AND CLAY
PtÀsTrclTY rN0Ex
FROM:Pit2O4.5'-5.5'
32X
HYOROMETER ANALYSIS SIEVE A,NALYSIS
¡IXE RüOINGs
2' HRS 7 HRSa3 ulf, ls utN 60!lN tsuñ
SERIES CLEAR
SANO GRAVËL
FINE MEDTUM lCOenSe FINE COARSE
18-7 -240 H.PryKUMAR GRADATION TEST RESULTS Fis. 3
H.P\KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. l8-7-240SOILTYPESilty Sand with GravelSilty Sand with GravelLIQUIDLIMITPLASTICINDEXUNCONFINEDCOMPRESS¡VESTRENGTHPÊRCENTPASSINGNO.200SIEVE383632SANDlY.l39GRAVEL(%"12629NATURALDRYDENSITYfocfìNATURALMOISTURECONTENT(o/ølDEPTH(ftt6r/z-7 Yz4V2-5 Y2PIT12