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Home My WebLink AboutSubsoil Study for Foundation Design 04.12.2018H-PVKUMAR Geotechnical Engineering I Engineering Geology Mate¡ials Testing I Environmentral $CA['åNEt) GARFIELD COUNTY, 5020 CountvRoad 154 cdMt\iùñlTf DEVELopMEûlenwood Spring_s, CO 81 601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa.com RECEIVED JUN I 4 2018 Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PR.OPOSED RESIDENCE 10325 COUNTY ROAD 331 GARFTELÐ COUNTY, COLORADO PR.OJECT NO. 18-7-182 APRIL 12,2018 PREPARED FOR: KIM AND CHRIS COLFLESH Ñ325 COUNTY ROAD 331 SILT, COLORADO 81652 kkconnell79 @ smail.com TABT,E OF CÛNTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION STTE CONDITIONS .... FIELD EXPLORATION SUBSURFACE CONDITIONS FO{.INDATION BEARING CONDITIONS DES IGN RECOMMENDATIONS FOUNDATIONS.. FLOOR SLABS.... UNDERDRAIN SYSTEM SURFACE DRAINAGE LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 through 7 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS ...... - I - I 1 2- -2- aJ- J 3 5 5 6 -7 - H.PèKUMAR Project No. 18-7-182 P{.}[TFÛSE ANÐ SCOPE {}F ST'T]ÐY This report presents the results of a subsoil study for a proposed residence to be locate d, at IO32S County Road 331 (Dry Hollow Roacl), south of Silt, Garfield County, Colorado. The project site is shown on Figure 1. The pulpose 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 Kim and Chris Colflesh dated February 27,2018. A field exploration program consisting of exploratory borings was conducted 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 recornmendations for foundation types, 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 constmction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The proposed residence will be a two story wood frame structure located on the property ås indicated on Figure 1. Grading for the structure is assumed to be relatively minor with cut depths between about 3 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 CONDITIONS The site is occupied by existing structures as shown on Figure 1 ancl has undergone some previous grading. The tenain is relatively flat with a slight slope down to the northwest H-P\KUÍVIAR Projecl No. 18-7-182 -2- becoming a strong slope away frclm the building area. Elevation difference across the building footprint is estimated at about 2 fent. Vegetation consists of grass and weeds. There is a concrete pad in the area of Boring 1. FIELD EXPLOR.ATION The field exploration for the project was conducted on March 6 and7,2018. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. Boring 2 was drilled further west of the proposed building than planned and in the area of the proposed septic disposal field. The borings were advanced with 4 inch diameter continuous flight augers powered by a truck-mounted CME-458 drill rig. The borings were logged by a representative of H-P/Kumar. Samples of the subsoils were taken with a 2 inch I.D. spoon sampler. The sampler was 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-15g6. 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 Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUtsSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils encountered at Boring 1 (located in the proposed building area) consisted of medium stiff' sandy silt and clay that became stiff with depth and extended down to the depth drilled of 36 feet. The subsoils encountered at Boring 2 (iocated to the west of the building area in a grass field), below about I foot of topsoil, consisted of very stiff, sandy silty clay rhat extended down to the depth drilled of 16 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density. Results of swell-consolidation testing performed on relatively undisturbed H-PÈKUIVIAR Project No. 18-7-182 -3- drive samples are presented on Iügures 4 through 7. 'l'be swell-consolidation test results indicate the very moist to wet soils at Boring I are generally moderately to highly compressible under conditions of loacling and wetting. The swell-consolidation test results also indicate the slightly moist and very stiff clay soils at Boring 2 are slightly compressible under conditions of loading and wetting with a low to moderate swell potential when wetted under a constant 1,000 psf surcharge. The laboratory testing is summarized in Table 1. Free water was encountered in Boring 1 at the time of drilling at a depth of about 16 feet and the soils were very moist to wet with depth. No free water was encountered in Boring 2 at the time of drilling and the soils were slightly moist. FOUNÐ.{TTO¡{ BII,&TTTNG CONÐTTIONS The subsoil conditions varied considerably between the borings, and could be variable in the foundation excavation for the building. Sprcad footing should be feasible for foundation support of the building with a risk of movement. The risk is due to the assumed variable bearing conditions, consisting of compressible soils at Boring l, and possibly expansive potential of the drier subsoils in the west part of the site. A lower risk foundation system would be helical piers or screw piles installed to depths of possibly 30 to 40 feet or more to achieve torque refusal. Micro-piles may also be feasible. Provided below are recommendations for a spread footing foundation. If recommendations at deep foundation are desired, we should be contacted. ÐESIGN RT'COMMENÐATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we believe the building can be foundeci with spread footings bearing on the natural soils and/or properly placed and compacted fill soils with some risk of movement H-PVKUTVIAR Project No. 18-7-182 -4- and distress. V/e shc¡uld evaluate the exposed bearing soils at the time of excavation for any needed sub-excavation and teplacement with aggregate base course soils below footing a.reas. The design and construction criteria presented below should be observed for a sprcad footing foundation system. 1) Footings placed on the undistulrbed natural soils and/or compacted structural fill should be designed for an allowable bearing pressute of 1,500 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 to IVz inches. If potentially expansive soils were to become wetted there could be additional movement. The magnitude of the potential movement would depend on the bearing conditions and depth and extent of the wetting. 2) The footings should have a minimum width of 18 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheatecl areas shoulcl be provided with adequate soil cover above their bearing elevation for frost protection. placement of foundations at least 36 inches below exterior grade is recommended for this area of Garfield County. 4) Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies and better withstand the effects of some differential movement such as by assuming an unsupported length of at least 15 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure coffesponding to an equivalent fluid unit weight of at least 55 pcf. 5) All existing fill, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the natural soils. The exposed soils in footing area should then be moistened and compacted. Soft soils may require drying and/or stabilization and potentially expansive soils may require removal and replacement with aggregate base course such as CDOT Class 5 or 6 material. Structural fill placed below footing areas should be compacted to at least gBVo standard Proctor density and a moisture content near optimum. H-PTKUIVIAR Projecl No. 18-7-182 -5- A rcpresentative of the geotechnical engineer should observe all footing excavations and test structural fill compaction prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade construction. There is a risk of slab movement due to potentially compressive soft subgrade or potentially expansive soils if they were to become wetted. Sub-excavation of a depth (typically 2 to 3 feet) and replacement with roaci base coultl be done to reduce the risk of movement. We should review the need for sub-excavation and replacement of the soils below floor slab areas at the time of construction. 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 requircments 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 sand and gravel, such as road base, should be placed beneath slabs for support and to facilitate drainage. This material should consist of minus 2 inch aggregate with at lea$ 5A7o retained on the No. 4 sieve and less fhan2To passing the No, 200 sieve. All fill materials for support of floor slabs should be compacted to at least 957o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site soils devoid of vegetation and topsoil. UNDERDRAIN SYSTEM Although free water was encountered during our exploration below probably excavation depth, it has been our experience in the area and where clay soils are present that local perched groundwater can develop during times of heavy precipitation or groundwater level can rise. Frozen ground during spring runoff can also create a perched condition. We recommend below- 6) H-P*KUIVIAR Project No. 18-7-'182 -6- grade constrtlction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressttrc buildup by an underdrain system, The crawlspace should be well vented. The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granular mate¡ial. The drain should be placed at each level of excavation and at least I foot below lowest adjacent finish grade and sloped at a minimu m lVo to a suitable gravity outlet or a sump whe¡e the water can be collected and pumped. Free-draining granular material used in the underdrain system should contain less th¿ur TEo passingthe No. 200 sieve, less fhan 507o 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. SURFACE DRAINAGE The following clrainage precautions shor¡ld 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 goVo of the maximum standard Proctor density in landscape areas. 3) The ground surface surrounding the exteriol'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. Free-draining wall backfill should be capped with about 2 feet of the on-site soils and filter fabric to reduce surface water infiltration. 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 foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by inigation. H-PùKUMAR Project No. 18-7-182 -7 - tr,IMTTATNONS This stucly has been conciucted in accordance with generally accepted geotechnical engineer.ing principles and practices in this arca at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtainecl from the exploratory borings drilled at the locations 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 interpolation and extrapolation of the subsurface conditions identified at the exploratory borings and variations in the subsurface conditions may not become evident until excavation is performed, If conditions encounterecl 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 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 fTll by a representative of the geotechnical engineer. Respectfully Submitted, I{-P\ KU David A. Young, P.E, Reviewed by: **/- ø Steven L. Pawlak, P.E. DAY/kac H-P*KU]VIAR Project No. 18-7-182 € * 10525 CoUNTY ROAD 53r 50 APPROXIMATE SCALE_FEET 0 18-7 -182 H-PryKUMAR TOCATION OF EXPLORATORY BORINGS Fig.1 ¡ Ê ç BORING 1 BORING 2 0 0 ôl t¿ WC=24.3 Dtl=97 38112 (rRoZrN) WC=7.2 DD¿ 1 26 5lAl 12 21 /12 10 108/ 12 WC=20.6 DÐ= 1 05 26/ 12 WC=7.9 DD=115 .Ê lq16112 WC= 18.9 DD= 1 07 15/ 12 t- rÁl l¡-lrr- ITf- L¡ 2s/12 2A È- LJIJtL IE¡- L¡JÕ 25 2524/12 WC=22.8 DD= 1 05 50 30 35 <q 17 /12 40 4A 18-7 *182 H.PVKUMAR LOGS OF TXPLORATORY BORINGS Fig. 2 I I LEGEND loPSolL; OROANIC STLTY cLAy, FIRM, SLtcHTLy MOIST, BROWN, RoOTs. :l_LI 4!!D- g.fAY {ML-CL);, sANDv, MEDTUM srtrF To slFF wtrH DEprH, vERy MCItsT ToWET, BROWN, LOW TO OCCASIONALLY MEDIUM PLASTICITY. cl-¡v (cl-); slLTY, sANDy, vERy sÏFF, sLtGHTLy Motsr, BRowN, MED|uM pLAsTlctTy. RELATIVELY UNDTSTURBED DRTVE SAMpLt; 2-tNCH LD. CAL|FORNtÀ LTNER SAMpLE. ¡¡,o DRIVE SAMPLE BLow couNï. tN0tcATES THAT 6 Blows oF A 140-pouND HAMMER"/ '' FALLTNG 30 rNcHEs wrnr neoúlÉsii'îo onrve rHE cALTFoRNTA r2 rNcHEs. -=- GROUNDWAIER LEVEL tN BORtNc AT TIME OF DRtLLtNc. -.} ÐEPTH BORING CAVED IMMÊÐIÂTELY FoLLowING ÐRILLING. NOTES hùt N -'vVIl4VI rvr)VI 1 1. THE EXPLORATCIRY BORINGS WERE DRILLED ON MARCH 6 AND 7,2018 WITH A 4-INCHDIAMETER CONTINUOUS FLIGHT POWER AUGER.. 2' THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMAîELY gY PACINGFROM FËATURES AT THE SITE. ,3. THE ELEVATIONS oF THE EXPLoRA¡oRv gonrNbs wERE NoT MEASUR€D AND THE LoGs oF îHEEXPLORATORY BORINGS ARE PLOTIEÐ TO DEPIH. 4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURAîT ONLY îO îHEOEGREE IMPLIED 8Y THT METHOD USEÐ. 5' THE LINES BETWEEN MATIRIALS SHOWN 9I THE EXPLORATORY B0R|NG LOGS RtpRtsENï îHtAPPROXIMATE souNDARles BETWEEN MATERIAL rvpÈs-ÀÑo iil rnaxslloNs u¡y si-cnaoual. 6' WATER LEVEL RTÄD'NGS WERT MADE AT THE TIME AND UNDER IHE CONDIÍIONS INDICATED.cRoUNDWATER wÄs Nor ENcoUNTERSD rN BoRTNG z. rlùcruiroNs rN GRouNDWATER LEVELMAY OCCUR OVER TIME. LABORATORY TEST RESULTS:wc = wATER CoNTENT (%) (ASTM D 2216);DD = DRY DENSITY (pcf) (ASTM D 2216).' 18-7-182 H.PryKUMAR LTGEND AND NOTTS Fig,3 3 SAMPLF CIF: Sondy Sitl cnd Cloy FROM; Boring 1 @' 2.5' tNC = 24.3 %, AÐ = 97 pcf 0 ^-1x JJ ¡¡J =(n I z.(] F_ (f, =()lnz.o(J 2 -3 4 _q -6 -7 *8 APPLIEO - KSF 100 : J t th; 5ç!ll ADD'TIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING-'---':"" --"f "' 1i:, I I I ] t I i a 1 I t t ! 1 I I i i I : ) I I t, I i i I I ) 1 l t t J l t I I I I 1 I I , i I I I 'i l I 18-7 *182 H-P*KUMAR SWTLL_CONSOLID,qTION TEST RTSULTS Fig. 4 3 ¡ fti Con!olidol¡st 'h SAMPLE OF: Sondy Sitt ond Ctoy FROM:BoringI@I0' WC = 20.6 %, tù = 1OS pcf ADDITIONAL COMPRTSSION UNOER CONSTANT PRESSURE DUE TO WETIING 0 -I n-2 JJ-J l"¡J3 tt1 t, -¿+z() tr ô Jovlzoo_6 -8 100 18-7-182 H-PryKI¡MAR SWTLL_CONSOLIDATION TEST RTSULTS Fig. 5 SAMPLE 0F: Sondy Sitty Cloy FR0M: Boring 1 @ 1S' WC = i 8.g %, DD = 107 pcf 0-4348. ADDITICINAL CCIMPRESSION UNDER CONSTANT PRESSURE DUE TO WÊTTING i J i I i I Ì I : I J I I : 1 I : i I : : : ! i 1 j I i t 1 1 I 1 t 1 l i 1 I ¡ I I 1 a I : i a i I t I t I I 1 ) ) t i i I t t : 1 : : t l 1 t I 1 1 i i I l t l I I I I I I I t 1 I { 1 , I'î' I t ! i t i I I 1 t I l I I I t I : : 1 1.0 .JJ l¡J3 v1 0 -1 zot- ô Joazo(J -5 -4 18-7 -182 H-PVKUMAR SWTLL_CONSOLIDAIION TTST RESULTS Fig. 6 € 2 , -l -¿ ñ JJ l¡J = I z() t- Õfo(nz o JJ L¡ =(/1 I zo Ë Õ:ioU'z (J APPLIËD 10 100 0 -1 -z *3 - KSr SAMPLE OF: Sondy Sitty Ctoy FROM: Boring2@'Z.S' WC = 7.2 %, ùÐ = 126 pcf EXPANSION UNDER CONSTANT PRESSURT UPON WÊTTINC SAMPLE OF: Sondy Sílty Ctoy FROM: Boring 2 @ 10' WC=7.9%,ÐÐ=fl5pcl th.ñ. EXPANSION UNDER CONSTANT PRESSURI UPON WETTING 18-7 *182 H-PryKUMAR SWELL-CONSOLIDATION TEST RISULTS Fis. 7 I{.PNKUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 18-7-182SOILTYPESandy Silt and ClaySandy Silt and ClaySandy Silry ClaySandy Silt and ClaySandy Silty ClaySandy Silt¡r CIayLIQUIDLIMITPLASTICINDEXUNCONFINEDCOMPRESSIVESTRENGTHPERCENTPASSINGNO.200SIEVEGRADATIONSAND(%)GRAVEL(o/'lNATURALDRYDENSITYlncfl97105t07105126115NATURALMOISTURECONTENTDEPTH24.320.618.922.87.27.9ZVz10I5252V2l0I SAMPLEIBORINGI2