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Home My WebLink AboutSoils Report 10.31.2006HEPWORTH - PAWLAK GEOTECH N ICAL October 31, 2006 I*lc[-*,-r¡ir' L-¿r', i¡L t.ìe,'r ¡ihl¡ i¡¡i, Irr. jilitl (.,rt::lrt Rr¡r.:.I l!4 { ilr'nl rrr,I Sl.r¡¡11., (.,,lrxrtr!' ì I Ófì I ll,':ir: Ì?i.ì- !).1 j - ?!l¡S F,n: 97t''-!)1i-5454 ellrr i i ; l:¡g,:,,t!:lii-ger;tt¡h.¡, r:l¡ H RECEIVED JUN 2 5 2018 GARFIELD COUNTY COMMUNITY DEVELOPMENTJoyce Kauffman P. O. Box 2571 Glenwood Springs, Colorado 81602 Job No.l06 0903 Subject Subsoil Study for Foundation Design, Proposed Residence, Lot 66, Filing 7, Elk Springs Subdivision, Aster Drive, Garfield County, Colorado Dear Ms. Kauffman: As requested, Hepworth-Pawlak Geotechnical, 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 October 16,2006. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Hepworth-Pawlak Geotechnical, Inc', previously performed a preliminary geotechnical study for Filings 6 through 9, Elk Springs (formerly Los Amigos Ranch PUD) and reported our findings on February 14, 1997, Job No. 197 617. Proposed Construction: Development plans for the lot were conceptual at the time of our;tudy. In general, the proposed residence will be one story wood frame construction above a walkout basement with an attached garage and located in the building envelope shown on Figure 1. Basement and garage floors will be slab-on-grade. Cut depths are expected to range between about 2 to 8 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: The site is located on a gently rolling upland mesa. Vegetation consists of grass and weeds with sage brush in the building envelope. The ground surface is relatively flat in the front part of the lot with a moderately to steep slope down to the southeast in the building envelope. A dry drainage is located just below most of the building envelope. Subsurf¡ce 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 presented on Figure 2. The subsoils encountered, below about one Pirrker 103,841-7119 . Lìrleirarlt¡ S|rings 7\q'$3-ii6J r Silvcrrhc¡r:rc 97tr-4ó8'1959 ô foot of topsoil, consist of slightly sandy clay. BasalT cobbles and boulclers in a silt and sand matrix was encountered in Pit 1 at 4 feet. The basalt soils are expected to continue with depth. Results of swell-consolidation testing performed on relatively undisturbed samples of the slightly sandy clay, presented on Figures 3 and 4, indicate low compressibility under existing moistute conditions anci light loatling antl a luw expansiort potential when wefted. No free water was observed in the pits at the time of excavation and the soils were slightly moist to moist. Foundation Recomnend¡tions: 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 soil designed for an allowable soil bearing pressure of 1,500 psffor support ofthe proposed residence. The clay soils tend to expand after wetting and there could be some post-construction foundation movement. The settlement could be differential depending on the extent of any wetting and for footings which transition between soil types. Footings should be a minimum width of 16 inches for eontinuous walls and 2 feet for columns. Utility tlenches and deep cuts into the basalt boulders will probably require heavy duty excâvation equipment and possibly chipping or blasting of large boulders. The topsoil and loose disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. Voids created from boulder removal at footing grade should be filled with a structural material such as road base compacted to at least 95 percent of standard Proctor density at a moisture content near optimum. 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 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 topsoil a¡d rocks larger than about 6 inches. Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to supporl lightly loaded slab-on-grade construction. There could be some potential slab heave if the clay soils are 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 un¡estrained vertical movement. Floor slab controljoints 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 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 thanZYo passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% 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. Job No.l06 0903 cåFtea-' -3 - Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the ¿rea that loüal perched groundwater can develop during timcs of hearr¡* precipitation or seasonal runofT. Frozen groutrd during spring runolTca¡t create a perched condition. We recommend below-grade construction, such as retaining walls ald basenent år'eas, be protected from wetting and hydrostatic pressure buildup by an underdraitr system. The drains should consist of 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 of excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum lYo to a suitable gravity outlet, Free-draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less thalr 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least I% feet deep. Sur{ace Drainage: 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 a¡rd underslab areas should be avoided during construction. Drying could increase the expansion potential of the clay soils. 2) Exterior backfill should be adjusted to neã optimum moisture and compacted to at least 95% of 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 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. lüe recommend a minimum slope of 12 inches in the first l0 feet in unpaved areas and a minimum slope of 3 inches in the fir$ l0 feel in pavement and walkway areas. A swale may be needed uphill to direct surface runoff arotrnd the residence. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy inigation and lawn sprinkler heads should be located at least l0 feet from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the foundation caused by irrigation. Limit¡tions: 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 about MOBC, then a professional in Job No.l06 0903 cå&ecn -4- 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 subsuface cc¡nditions may not become evident until excavation is performed. If conditions encountered during construction appe¿r different from those described in this report, we should be notified at once so re-evaluatio¡r of the recummentlatio¡ts rnay 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 recommendations, and to veri$ 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, . PAWLAK GEOTEC}INICAL, INC. L/ouis E. Eller Reviewed by Steven L. Pawlak, P LEElksw attachments Figure I - Figure 2 - Pits Logs of Pits Figures 3 and 4 * Swell-Consolidation Test Results Table I - Summary of Laboratory Test Results ataa a aa È Job No. 106 0903 cå8tecrr APPROXIMATE SCALE 1'' :80' -n*** LOT 66 PIT 1 /I nn 4 r LOT 68 gUILDING ENVELOPÊ LOT 64 ¡ I ) I ¿¿t PIT 2 1 06 0903 LOCATION OF EXPLORATORY PITS Figure 1 PIT 1 PIT 2 0 l{C=11.4 DD:11J0 -200=92 WC=9.a DD=97 IOPSOIL; organic sandy silt and clay, firm, moist. dark brown. CLAY (CL); slightly sândy, stiff to very stiff, moist, reddish brown. 0 o)oIL E o-oo 5 {¡)(¡) l_L It o- 0)c) wc--13.8 DD-1'10 '10 5 10 LËGËND: BASALT COBBLES AND BOULDËRS (GM); in a silt ând sand rnatrix, dense, stightty moist to moist, light brown to white, calcareous. Boulders up to 3 feet encountered. 2" Diameter hand driven liner sample. NOTES: '1. Exploratory pits were excavated on october 24,20a6 with a cat 420D backhoe. 2' Locations of exploratory piis were rneasured approx¡rnately by pacing from features shown on the site plan provided. 3. Elevations of exploratory pits were not measured and the logs of exploratory pits âre drawn to deplh. 4. Ïhe exploratory pit locations should be considered accurate only to the degree lmplied by the method used. 5. Ïhe lines between materials shown on the exploratory pil logs represent the approximate boundaries between material types and transitions may be gradual. 6' No free water was encountered in the pits al the time of excavating. Fluctuatíon in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content (%) DD = Dry Density (pcf) -2AA : Percent pass¡ng No. 200 sieve w þ /l 1 06 0903 LOGS OF FXPLORATORY PITS Figure 2 ðec .qØt.úo-X LU co øo g Eoo 2 0.1 1.0 10 100 APPLIED PRESSURE - ksf àsc 'ıcr!o-XtU I C ,ı U) cL Eorì 0 2 10 APPL,ED PRESSURE - ksf Moisture Content = 11.4 Üry Densify = 109 Sample of: Stighily Sandy Ctay From: Pít 1 at 2 Feet percenl pcf \ t h$ Expansíon upon wetting Moisture Content : 9.4 Dry Densily: 97 Sample of: Slightly Sandy Clay From: Pit 1 at3/zFeet percent pcf ( ï ) è $ È.xpansron upon wettinq 0.1 1.0 100 106 0903 SWËLL-CON SOLI DATION TEST RËSULTS Figure 3 Moisture Content : 13.8 Dry DensitY = 110 Sample of: Slightly Sandy clay From: Pit 2 at1TzFeel percent pcf lk-illï) È \)il Expànsion upon wetting il il il à€co'ı (6 o-xLrl E _oa at, {L) u E (-) 1 0 I 2 10 APPLIED PRESSURE - ksf 0.1 1.0 100 106 0903 SWELL-CON SOLI DATION TEST R ESU LTS Figure 4 HEPWORTH-PAWI.AK GEOTECHNICAL, INC.TABLE 1SUMMARY OF LABORATORY TEST RESULTSJob No. 106 0903SOIL ORBEDROCK TYPESlightly Sandy ClaySlightly Sardy ClaySlightly Sandy ClayUQUIDLIMITpt¡sTIcINDEXUNCONFINEDCOMPR.ESSIVESTREN6THGRAVÊLSANDPERCENTPASSINGNO.200SIÊVÊeÁ)(7o)92NATURALDRYDENSTTYlDcfl10997110PITDEPTHNATUR.ALMOISTURECONTENT11.49.413.823U23 LlzI2