HomeMy WebLinkAboutSoils Report 04.06.2018H-PVKUMAR 5020 County Road 154
Glenwood Springs, CO 8f 601
Phone: (970) 945-7988
Far (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
April6,2018
lVendy Gaylord
P.O. Box 3361
Basalt, Colorado 81621
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y I ol'd @ gur ilil .ç_ol rt
Pmject No.18-7-203
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot M-9, Midland
Point, Midland Point Road, Garfield County, Colorado
Dear Ms. Gaylord:
As requested, H-P/Kumar performed a subsoil study for design of foundations ât the subject site.
The study was conducted in accordance with our agreement for geotechnical engineering
services to you dated March 15, 2018. The data obtained and our recommendations based on the
proposed construction arid subsurface conditions encountered are presented in this report.
Proposed Construction: The proposed residence will be single-story and located on the site as
shown on Figure l. Ground floors could be structural above crawlspace for the residence and
slab-on-grade for the garage.' Cut depths are expected to range between about 3 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 signifîcantly different from those described
above, we should be notified to re-evaluate the recornmendations presented in this report.
Site Conditions: The lot was vacant and had been graded with mainly shallow fills ar the time
of our study. A berm and ditch roughly 3 to I feet high follows the front, western part of the lot.
A fill stockpile about 5 to 6 feet high extends into the south part of the lot and the east part
outside of the building envelope slopes steeply down to the east. Most of the middle lot building
area is relatively flat with a gentle slope down to the north. Vegetation consists of grass, weeds
and sage brush.
Geotechnical Enginaering I Engineering Geology
Materials Testing I Environmentral
aL-
Subsidence Fotential: Midland Point subdivision is underlain by Pennsylvania Age Eagle
Valley Evaporite bedrock. The evaporite contains gypsum cleposits. f)issalution of the gypsum
under certain conditions can cause sinkholes to develop and can produce areas oflocalized
subsidence. Sinkholes have been observed scattered throughout the lower Roaring Fork River
valley. Sinkholes were not observed in the immediate area of the subject lot and no indications
of subsurface voids were observed in the exploratory pits on the lot. Based on our present
knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our
opinion, the risk of ground subsidence at Lot M-9 throughout the service life of the proposed
residence is low and similar to other lots in the area but the o\ryner should be aware of the
potential for sinkhole development.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating 2
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 3 feet of silty to clayey gravel and
cobble fill in Pit I and I foot of topsoil and?Vz feet of silty sandy clay in Pit 2, consist of
relatively dense, slightly silty sandy gravel and cobbles. Results of swell-consolidation testing
performed on a relatively undisturbed sample of the sandy clay, presented on Figure 3, indicate
low to moderate compressibility under conditions of loading and wetting with a low collapse
potential (settlement under constant load) when wetted. Results of a gradation analysis
performed on a sample of natural sandy gravel (minus 5-inch fraction) obtained from Pit 2 are
presented on Figure 4. 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 recomrnend spread footings
placed on the undisturbed natural granular soil below existing fill and clay soils designed for an
allowable soil bearing pressure of 3,000 psf for suppotr of the proposed residence. The clay soils
tend to compress after wetting and should be removed from below footing areas. Structural fill
compacted to at least 987o of standard Proctor density can be used to reestablish design bearing
level. Post-construction foundation settlements are expected to be less than I inch. Footings
should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Existing
fill, topsoil and loose disturbed soils encountered in footing areas should be removed down to the
-3-
undisturbed natural granular soils. We should observe the completed foundation excavation for
bearing conditions prior to footing construction or placement of backfill. 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.
Coniinuous 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 excluding organics and rock larger than 6
inches.
Floor Slabsr The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction. The natural clay soils may have some potential for settlement if
wetted. 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 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 5OVo passing the No. 4 sieve and
less than l27o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Vo 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: It is our understanding the proposed fînished floor elevation at the lowest
level will be at or above the surrounding grade and the crawlspace will be relatively shallow,
about 3 feet deep. Therefore, a foundation drain system is not required. 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 and basement
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areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall
drain system.
If the finished floor elevation of the proposed structure is revised to have a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
Surface Ðnainage: The following drainage precautions should be observed during construction
and maintained 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 95Vo of the maximum standard Proctor density in pavement and slab areas
and to at least 90lo of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill 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 first 10 feet in unpaved areas and a minimum slope of 3
inches in the first l0 feet in pavement and walkway areas.
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.
Lirnitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at this time. lVe 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,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
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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
recofirmendations may be made.
This report has been prepared for the exclusive use by our client for design purposes. \t{e are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation and fîeld services during construction to review and
monitor the implementation of our recommendâtions, 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,
H.PTKUIVIAR
Steven L. Pawlak,
Reviewed by:
Daniel E. Hardin, P.E.
SLP/kac
Attachments: Figure I * Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test Results
Figure 4 - Gradation Test Results
Table I - Summary of Laboratory Test Results
cc: Ken lannaccone, P.E. (Lc,,-tl@)¡tt}tç"!ilt'4hs,slìut1lc_tJ"!ql)
¡¡ICJLAI'¡D POiiiT R ÔA D
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PIT I
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LOT M-9
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APPROXIMATE SCALE_FEET
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18-7-203 H.PVKIIMAP LOCATION OF FXPI ORATôPY PITç Eia f
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PIT 1
EL. 994'
PIT 2
EL. 991 .5'
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WC=6.'l
DD= I 03
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-tt +4=74
-' -200=5
10 10
TOPSOIL; ORGANIC SANDY SILT AND CLAY, MOIST, DARK BROWN.
FILL; SILTY CLAYEY SANDY GRAVEL AND COBBLES, LOOSE, MTXED BROWN
CLAY (SC-CL); VERV SANDY, SILTY, VERY STIFF, SLIGHTLY MOIST, BROWN
GRAVET AND COBBLES
MOIST, BROWN, ROUND
(GM-GP); SLIGHTLY SILTY, SANDY. SMALL BoULOERS, DENSE, SLIGHTLY
ED ROCK.
þ HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE
t,DISÏURBED BULK SAMPLE.
NOTES_
1. THE EXPLORATORY PITS $/ERE EXCAVATED WITH A BACKHOE ON MARCH 29, 2018.
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 INÎERPOLATION EETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURAÎE 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 gE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OT DIGGING
7. LABORATORY TTST RESULTS:
WC = WATER CoNTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCf) (ASTM D 2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE
-200 = PERCENTAGE PASSING NO. 200 StEyE
(AsrM D a22);(rsru D 1t4o).
*
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18-7-203 H-PVKUMAR LOGS OF EXPLORATORY PITS fi¡- ?
SAMPLE OF: Very Sondy Ctoy
FROM:Pit2l.e.2'
WC = 6.1 9á, Ðù = .l03 pcf
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE 10 WETTING
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18-7-203 H-PTKUIVIAR SWTLL-CONSOLIDATICIN TTST RTSULTS Fig. 3
HYONOMEIET AN,ÀLYSIS
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SAND GRAVEL
FINE MEDTUM lcoanse FINE COARSE
SlËvÉ A''IALYSIS
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CLAY 10 SILI COBgLES
GRAVEL ?1 '4 SAND 21 )I
LroulD tlMlT PtasïtcrTY TNDEX
SAMFLE OF: Slighlly Sllty Sondy Grovel *¡th Cobbtôs
SILÏ ANO CI.AY S X
FROM:Pil 2O3.5'-6.5'
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1 8-7-203 H-PÈKUIVIAR GRADATION TTST RESULTS Fig. a
9"3-TNKUHVII\Ë{TABLË 1SUMMARY OF LABORATORY TEST RESULTSProject ftlo. {8-7-203PIT2SOILTYPEVery Sandy ClaySlightly Silty Sandy Gravelwith CobblesfosflUNCONFINEDCOMPRESSIVESTRENGTH(%\PLASTICINDEXATTERBERG LIMITSLIQUIDLIMITlù/"\PERCENTPASSINGNO.200SIEVE51274NATURALDRYDENSITYl%',SAND(%',GRAVEL103NATURALMOISTURECONTENTDEPTH6.125Yz-6Y,