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Home My WebLink AboutSubsoil Study for Foundation Design 02.08.18H.PVKUMAR Geotedrnlcal Engineerlng I Englnearlng Geology Materials Tasting I Environmenùal 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax (970) 945-84s4 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado ST]BSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RBSIDENCE LOT 10, BLOCK 7, BATTLBMENT CREEK VILLAGE 284 MEADO\ry CREEK DRIVE GaRFIELD COUNTY, COLORADO PROJECT NO. 17.7-868 FEBRUARY 8,2018 PREPARED FOR: RUSSELL AND LORI CARTWRIGHT 18 VALLEY VIE\ry PLACE PARACIIUTE, COLORADO 81635 @ TABLE OF CONTENTS PI.JRPOSE AND SCOPE OF STUDY PROPOSF,D CONSTRI ]CTTON SME CONDITIONS FIELD EXPLORATION S T.JBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS FLOOR SLABS UNDERDRAIN SYSTEM ........ SURFACE DRAINAGE LIMITATIONS........ FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURE 3 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS -1- _t _ 1 -2- -2- ....- 3 - ........- 3 - ........- 3 - ........- 4 - -\- 5- 6- H-P*I(JIVAR Project No. 17-7-868 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at Lot 10, Block T,Baftlement Creek Village, Battlement Mesa, 284 Meadow Creek Drive, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Russell and Lori Cartwright dated December 13,2017. An exploratory boring was drilled to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification, compressibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recommendations for founclation tlpes, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The proposed residence will be a one story, wood-frame structure with an attached IVz story garage. Ground floors will be structural over crawlspace, with slab-on-grade in the garage. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 4 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. Ifbuilding loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITTONS The site was vacant at the time of field exploration. The lot is bounded by Meadow Creek Drive on the northwest, a vacant lot to the southwest and nearby developed lots on the other sides. The H-P*KUÍVIAR Project No. 17-7-868 ı terrain is relatively flat and gently sloping dowu to the north. Two apparently recently excavated and backfilled pits were visible on the site. Vegetation consisted of grass and weeds. The residences in the vicinity were one and two stories in height. FIELD EXPLORATION The field exploration for the project was conducted on December 20,20L7. One exploratory boring was drilled at the location shown on Figure 1 to evaluate the general subsurface conditions. The boring was advanced with 4 inch diameter continuous flight augers powered by a truck-mounted CME-458 drill rig. The boring was logged by a representative of H-P/Kumar. Samples of the subsoils were taken with 1% inch and 2 inch I.D. spoon samplers. The samplers were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values are shown on the Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist ofabout Vzfeet oftopsoil overlying stiffto very stiff, sandy silt and clay to a depth of about 18 feet where underlain by relatively dense, silty to very silty sandy basalt gravels and cobbles with boulders to the drilled depth of 26 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and dry density, and finer than sand size gradation analyses. Results of swell-. consolidation testing performed on relatively undisturbed drive samples of the silt and clay soils are presented on Figure 3. The silt and clay sample from}Yz feet depth showed low to moderate compressibility under conditions of loading and wetting with a low hydro-compression potential. The silt and clay sample from 10 feet in depth showed low compressibility under a constant light H.PùKUMAR Project No. '17.7-868 -J- surcharge with low expansioll upon wetting and moderate cornpressibility when loaded after wetting. The laboratory testing is summarized in Table l. No free water was encountered in thc boring at the time of drilling and the subsoils were slightly rnuist. FOUNDATION BEARING CONDITIONS The sandy silt and clay soils encountered at shallow cut depth tend to compress when wetted under load. Lightly loaded spread footings bearing on these soils can be used for foundation support of thc resitlence with some risk of settlement and building distress, primarily if the bearing soils become wetted. Sources of wetting include excessive inigation near the foundation, poor surface drainage adjacent to foundation walls and utility line leaks. Cut depth for the foundation should be limited to about 3 feet due to the underlying potentially expansive soils. A deep foundation system, such as helical piers or micro-piles, extending down into the dense coarse granular soils could be used to provide a low risk of building settlement and distress. Below are recoÍtmendations for a spread footing foundation bearing on natural subsoils. If recommendations for a deep foundation system are desired, we should be contacted. DESIGN RECOMMENDATIONS FOTINDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural fine-grained soils with some risk of movement. Precautions should be taken to prevent wetting of the bearing soils. The design and construction criteria presented below should be observed for a spread footing foundation system. H-PèKUTVIAR Projecl No. 17-7-868 -4- 1)Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, \rye expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. There could be some additional settlement if the bearing soils were to become wetted. The magnitude of the additional settlement would depend on the depth and extent of the wetting but may be on the order of % to I inch. The footings should have a minimum width of 20 inches for continuous walls and 2 feet for isolated pads. Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this afea. Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies and better withstand the effects of some differential settlement such as by assuming an unsupported length of at least 14 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure corresponding to an equivalent fluid unit weight of at least 50 pcf. Any existing fill, all topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the undisturbed natural soils. The exposed soils in footing area should then be moistened and compacted. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions, 2) 3) 4) FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction with a risk of settlement if the slab subgrade were to become 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 ¡einforcement should be established by the designer based on experience and 5) 6) H-PVKUIVIAR Project No. 17-7-868 -5- the intended slab use. A minimun 4 inch layer of sand and gravel road base should be placed beneath slabs for support and to facilitate drainage. This mate¡ial should consist of minus 2 inch aggregate with at least 50Vo retained on the No. 4 sieve and less than l2%o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at leastg57o of maximum standard Proctor density at a moisture content near optimum. Required fîll can consist of the on- site soils devoid ofvegetation, topsoil and oversized rocks. I.JNDERDRAIN SYSTEM Ifthe ground-level finished floor elevation ofthe residence is at or above the surrounding grade, as planned, 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 also can create a perched condition. An underdrain system is not recommended around the planned shallow crawlspace area to help timit the potential for wetting below the shallow footings. We recommend below-grade construction, such as retaining walls, 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 surrounded above the invert level with free-draining granular material. The drain should be placed at least 1 foot below lowest adjacent finish grade and sloped at a minimum lVo to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than ZVo passingthe No. 200 sieve, less than 50Zo passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should lre at least lVz feet deep and be covered by filter fabric. SURFACE DRAINAGE Providing proper grading and drainage around the buildings will be critical to limiting subsurface wetting and adequate performance of the structure. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: H-P*KUIVIAR Project No. 17-7-868 2) 1) 3) 4) -6- Inundation ofthe foundation excavations and underslab areas should be avoided during construction. 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 9O7o of the maximum standard Proctor density in landscape areas, The ground surface sunounding 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 paved areas. Roof downspouts ancl clrains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy irrigation should be located at least l0 feet from foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by inigation. s) LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. rù/e make no waffanty either express or implied. The conclusions and recommendations submitted in this repoü are based upon the data obtained from the exploratory boring drilled at the location indicated on Figure 1, 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 this special field of practice should be consulted. Our findings include extrapolation of the subsurface conditions identified at the exploratory boring 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 so that 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 H-PVKU]VIAR Project No. 17-7-868 -7 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. Respectfully Submitted, H-P\ KUMAR //-/hb Shane M. Mello, Staff Reviewed David A. Young, P SMMlkac H-Prv¡1¡¡¡Y¡¡¡ Prniont Àln l7-7-QAa ¡, -/f**Jñ's- - I GÂRAGE BORING I PROPOSEÐ RESIDENCE LOT 1O 284 MEADOW CREEK ÐRIVE APPROXIMATE SCALE-FEET 17 -7-868 H.PryKUMAR LOCATION OF EXPLORATORY BORING Fig. f "t *?. I 3j ç e BORING 1 LEqEND 0 I0PS0IL oRcANtc sANoy st$, Motsï, DARK BR0WN. t4/1? WC=5.6 DD= I 07 stLr AND Ct Ay (ML-CL); SANDY, SnFF f0 vFRy sTtFF l'/tTH DTPÏH, SLIGHTLY MOIST, 8ROWN. tr 14112 WC=4.2 D0= I 01 -200=89 BASALT GRÀVEL AND c0EBLtS (GU); TROSISLE 9OULDERS, SANDY SILT'Í TO VERY SILTY, DENSE, SLIGHTLY MOIST, GRAY-BROWN. ! i DRIVE SAMPLE, 2-INCH I.D. CÂLIFORNIA UNER SAMPLE. 10 2s/12 WC=4.6 DRIVE SAMPLE, I 3/6-|NCH t.D. SpLtT Sp00N 5ïÂNDARD PENTTRATION TT5I,DD=l 1 1 F-t!l¡t! IT!-fL t¡J 1¿717 0RIVE SAMPLE 8L0W COUNT. INDICÀTES THAT tl BL0WS 0F.', .- A 140-POUNO HAMMER FALLING 30 INCHES WERE NEOUIREO TO DRIVT THE SÀMPLER 12 INCHES. 15 8t112 WC=5.0 NOTES I. THE EXPTORÀTORY BORING WAS DRITLTO ON OTCTMBER ZE,2OI7 WITH A I-INCH OIAMETER CONTINUOUS FLIGHT POWTR AUOER. 2. THE LOCATION OF THT EXPLORATORY BORING I1¡ÄS I{TASUREO APPROXIMAIELY BY PACING FROM FSATURES SHOWN ON THE SIII PtÂN PRoVlDto. DD=1 1 f -200=87 20 48/12 25 50/3 3. THE TLTVATION OF THE EXPLORATORY BORING WAS NOT MTASURED AND ÏHE LOG OF THE EXPLORATORY SORING IS PLOTTED TO ÐEPTH. 1, THE TXPLORATORY BORINO LOCÁTION SHOULD 8T CONSIDTREO ACCURAÏE ONLY TO THE DECREE IMPLIEO BY THE METHOD USED. 5. T}IE LINIS EETWTIN MATERIALS SHOI{N ON THT TXPLORATORY BORING LOG REPRTSENI THE ÂPPROXIMATE EOUNDARITS BETWIEN HÀTERIAL TYPES AND THE TRÀNSITIONS MÅY BT GRADUAL. 6, EROUNOWATER WAS NOT ENCOUNTERIO IN THE EORINC AT rHE IIMT OF ÐRILLING. 7, LÂEORAIORY TTST RESULIS: WC = 'fiATtR C0NIENT (Z) (ASTM 0 2216); DD = DRY ÐENSITY (PCf) {ASTM D 2216); -200 ; PERCENTAGE PASSTNG N0. 200 S|EVÊ (ÀSIM D trdo). 30 1 7-7*868 H.PryKUMAR LOG OF EXPLORATORY BORING Fig. 2 I SAMPLE OF: Sondy Sill cnd Cloy FROM:Boringlae.2.5' WC = 6.6 %, ÐD = 't07 pcf 1 i ta,1 1l ': t. ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING :I JJl¡l =¡n I otr o JoØzo(J x JJ l¡J =U1 I za F â Jo zo(J 0 -1 2 _? -4 0 -2 . KSF APPLIED SAMPLT OF: Scndy Silt ond Clcy FROM: Eoring 1 @ 'l 0' WC = 4.6 %, DÐ ='l lt pcf t,0 100 1 7-7-868 H-PryKUMAR SWTLL_CONSOLIDATION TEST RESULTS Fig. 3 H-P\KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 17-7-868SOILTYPESandy Silt and ClaySandy Silt and ClaySandy Silt and ClaySandy Silt and ClayUNCONFINEDCOMPRESSIVESTRENGTH(PSF)ATTERBERG LIMITSPl-ASTtCINDEX(%lLIQUIDLIMIT(%lPERCENTPASSINGNO.200SIEVE8987SAND(YolGRAVEL(o/olNATURALMOISTURECONTENTNATURALDRYDENSITYr0710r1111116.64.24.65.0BORINGDEPTH12%510I5