HomeMy WebLinkAboutSubsoil StudyH-PVKUMAR
9eotechnlcal Engineering I Engineering Geology
Matedals Testing I Environmental -
5020 County Road 154
Glenwood co 81601
945-7988
94S8454
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Offiæ Locations: Denver (He), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
November 29,2018
Daniel & Donna Miller
c/o Dan Gruenefeldt
P. O. Box l910
Basalt, Colorado 81621
dau(Eeruç¡¡çfeldlçam
Project No.l8-7-630
Subject: Subsoil Study for Foundation Design, Proposed Resideirce(s), Lots 4l and 42,
Roaring Fork Mesa, Aspen Glen Subdivision,2l Tellico Court and79 Golden
Stone Drive, Garfield County, Colorado
Dear Dan:
As requested, H-P/I(umar performed a subsoil study for design of foundations at the subject
sites. The study was conducted in accordance with our agreement for geotechnical engineering
sei:r¡ices to Daniel and Donna Miller dated October 10, 2018. The data obtaine.d and our
recommendations based on the proposed constn¡ction and subsr¡rface conditions encountered are
presented in this report.
Proposed Constructlon: We understand that the properties may be developed with a single
family residencc on each lot or the lots may be combined with one residence on the combined
Iots. We assume the proposed residenc{s) will be one to two story wood &ame structures over
full basemqtt or crawlspace with attached garage. Basement and garage floors will be slab-on-
grade. Cut depths are expectd to range between about 3 to l0 feet. Foundation loadings for this
tlpe of construction are assumed to be relatively light and t¡,pical of the proposed t¡pe of
construction.
Ifbuilding conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Slte Conditlons: The lots were vacant at the time of our site visit. The lots are relatively flat
and slope gently down to the south-southeast. There is a shallow pond located on the north side
ofboth lots. Vegetation consists of grass and weds. There has likely been overlot grading and
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site disturbance during subdivision development particularly around the parts of the lots adjacent
to the pond and roadways.
Subsidence Potential: Aspen Glen is underlain by Pennsylvania Age Eagle Valley Evaporite
bedrock. The evaporite contains gypsum dqosits. Dissolution of the g)?sum under certain
conditions can cause sinkholes to develop and can produce areas of loc alizedsubsidence.
During previous work in the area, sinlúroles were obsen¡ed in Aspør Glen, mainly on the east
side of the Roaring Fork River. The closest mapped sinkhole on the west side of the river is
about 3,000 feet northwest of Lots 41 and 42. The nearest mapped sinkhole on the east side of
the river is about 2,000 feet to the east. Sinkholes were not observed in the immediate area of
the subject tot. Based on our present knowledge of the site, it cannot be said for certain that
sinklroles will not develop. In our opinion, the risk of ground subside,nce at Lots 4l and 42 is
low and similar to other lots in the area but the owner should be aware of the potential for
sir¡khole development.
Subsurface Conditions: The subsurface conditions at thc site were evaluated by excavating 7
exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The zubsoils encountered, below about I foot of topsoil, consist of I to
4tA feæt of stiff, sandy silty clay overlying relatively dense silty sandy gravel with cobbles and
small boulders. The de,nse gravel was encountered at depths of 2 to SYzfeetand extended down
to the maximum depth explored of 6 feet. In general, the greater depths to gravels were
encountered in the higher elevation pits on the north side of the lots (Pits 3, 4 and 6). Refusal to
baclÍroe digging was encountered at the bottom of all seven pits at depths of ZVzto 6 fect.
Results of swell-consolidation testing performed on relatively undisturted samples of the
shallow clay soils, presented on Figures 4 and 5, indicate low compressibility under existing low
moisture condition and light loading and a low collapse potential (settlement under constant
load) when wetted. The clay samples were moderately to highly compressible under increased
loading after wetting. No free water was observed in the pits at the time of excavation and the
soils were slightly moist to moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and thc nature of the proposed construction, trye recoûtmend spread footings
H.PÈKUMAR
Projecl No. 18-7-630
3
placed on the undisturbed natural gravel soil þelow all clay soils) designed for an allowable soil
bearing pressure of 3,000 psf for support of the proposed residenc{s). Footings should be a
minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed
soils and existing fill and clay soils encountered at the foundation bearing level within the
excavation should be removed and the footing bearing level extended down to the undisturbed
natural gravel soils. Exterior footings should be provided with adequate cover above their
bearing elevations for frost protection. Placement of footings at least 3ó 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 æ by assuming an unsupported length of at least l0
feet. Foundation walls acting as retaining structures should be designed to resist a lateral earth
pressure based on an oquivalent fluid unit weight of at least 50 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightty loaded
slab'on-grade construction. The upper clay soils have a potential to settle when wetted similar to
that described above. To reduce the effects of some differential moveÍrent, floor slabs should be
separated from all bearing walls and columns with expansion joints which allow unreshained
vertical movement. Floor slab conhol joints should be used to reduce damage due to shrinkage
cracking. The requireinents 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 free-
draining gravel should be placed beneath basement level slabs to facilitate drainage. This
material should consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and
less than 2% passing the No. 200 sieve.
All ûll 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 gravel soils or imported road base gravel devoid of vegetation, topsoil and oversized rock.
Underdrain System: Although free water was not encountered during our exploration, it has
been our experietrce in this area that local perched groundwater can develop during times of
heavy precipitation or seasonal runoff Frozen ground during spring runoff can ereate a perched
condition. We recommend below-grade construction, such as retaining walls, crawlspace and
H-P+KUMAR
Projecl No. 18-7430
4
basement areas, 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 lo/o to
a suitable gravity outlet, drywell or sump and pump. Free-draining granular material used in the
underdrain system should contain less than 2o/o passingthe 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 lYzfeetdeep.
Surf¡ce DraÍnage: The following drainage precautions should be observed during construction
and maintained at all times after the residence(s) has/have been coinpleted:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exteriorbackfill should be adjusted to near optimum moisture and compacted to
at least 95% of the maximum standard Proctor density in pavonent and slab areas
and to at least 90% of the mærimum standard Proctor density in landscape areas.
Free-draining wall backfill should be capped with about 2 feetof 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. rile recommend a minirnum
slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the ñrst l0 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. We make no waranty either
express or implied. The conclusions and recommendations submitted in this repof 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 tlpe of construction, and our experience in
H-PÈKUMAR
Projec{ No. 18-7-830
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the area. Our services do not include determining the presence, prevention or possibility of mold
or other biological contaminants (MOBC) developing in the fi¡ture. If ttre 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 maynot 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
recommendations may be made.
This report has been prepared for the exclusive use by our client for desígn purposes. Vy'e are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation and field services during constn¡ction to review and
monitor the implernentation of our recorlmendations, and to veris that the recommendations
have been appropriately interpreted, Significant design changes may require additional analysis
or modifications to the recommendations presented herein. Vy'e recommend on-site observation
of excavations and foundation bearing strata and testing of stluctural fill by a represe,ntative of
the geotechnical engineer.
If you have any questions or if we may be of further assistanceo please lot us know.
Respectfu lly Submitted,
H.P+KUMAR
Daniel E. Hardin, P
Reviewed by:
Steven L. Pawlak, P.E.
DEH/kac
attachments Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Legend and Notes
Figures 4 and 5 - Swell-Consolidation Test Results
Table 1 - Summary of Laboratory Test Results
H-PÈKUMAR
Projecl Nû. '18-7-630
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1 8-7-63CI H-PryKUMAR LOGS OT EXPLCIRATORY PITS Fig. 2
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TOPSOIL, ORGANIC SANDY, SILTY CLAY, FIRM, MOIST, DARK BROWN.
ctAY (cL): stLTY SANDY, ST|FF, SLtGl.tTLy MO|ST, BROWN
GRAVEL AND SILT (CL-Ut_): SANDY, ST|FF, SL|GHTLY MO|ST, REDDTSH BROWN.
GRAVEL
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(GM) SANDY, StLTy W|TH COBBLES AND SMALL BOULDERS, DENSE, SLtct{TLy MOIST,
ROWN TO REDDISH BROWN.
þ HAND DRIVEN z_INCH DIAMETER LINER SAMPLE.
t PRACÏICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATTD WITH A BACKHOE ON NOVEMBER 14, 2018.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. fHI ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4, THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY
TO THE DTGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON TI{E EXPLORATORY PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWAÏER WAS NOT ENCOUNTERED IN THE PITS AT THE ÎIME OF DIGGING. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7, LABORATORY TEST RESULTS:
wc = WATER CCINTENT (,6) (ASTM D 2216);
DD = DRY DENSITY (pcf) (lsru D 2216).
1 8-7-630 H-PæKUMAR LEGEND AND NOTES Fig. 3
SAMPLE OF: Sondy Sitty Ctoy
FROM: Pit I O 1.5'
WC = /.5 ?4, Dt = 89 pcf
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1 8-7-630 H.PryKUTVIAR SWELL-CONSOLIDATION TEST RESULTS Fig. 4
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1 8-7-630 H-PryKUIVIAR SWELL-CONSOLIDATION TEST RESULTS Fig. 5
H-PtKUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProþct No. 18-7-6307IPffSAHPLE LOCANON,}LlYzDEPTT{ffr¡7.77.6NATURÂLtotsluRECOilTENTP/"18589NATURALDRYDENSITYlDcfìGRAVEL(/rlGRADAΡONSAND(%lPEßCEMTPASSINGNO.zfl)SIEl'ELIQUIDLtf[tTIVolPLASiT|CINDEXlo/"1UNCONFINEDCOTPRESSIVESTRENGTHlcf¡Sandy Silty ClaySandy Silty ClaySOILTYPE