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Home My WebLink AboutSubsoils Study for Foundation DesignH-PVKUMAR Geotechnical Engineering I Engineering Geology Materials Testing I Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax (970)945-M54 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 43, OAK MBADOWS FILING 48, PHASE II 657 OLD 1VIIDLAND SPUR GARFIELD COUNTY, COLORADO PROJECT NO.t7-7-697 ocToBER 30,2017 PREPARED FOR: STEVE SPILLANIÙ 264BUCKTHORN NEW CASTLE, COLORADO 81647 (spillanes @ hotmail.com) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS GEOLOGIC CONDITIONS FIELD EXPLORATION ...... SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS ......... DESIGN RECOMMENDATIONS FOIJNDATIONS.. FOUNDATION AND RETAINING TVALLS FLOOR SLABS UNDERDRAIN SYSTEM. SITE GRADING ..........,..... SURFACE DRAINAGE.... LIMITATIONS,,,,.......... FIGURE I - 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 ....- 1 - I _) _ ......- 2 - 1 -2- -3- -3- -8- H.P*KUMAR Proiect No. 17-7-697 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 43, OakMeadows, Filing 48, Phase 11,657 Old Midland Spur, Garfield County, Colorado. The project site is shown on Figure L 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 Steve Spillane dated September 14,2017. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the ñeld 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 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 construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION At the time of our study, design plans for the residence had not been developed. In general, the residence will be located in the middle to northern part of the lot roughly as shown on Figure I and will likely have a walkout lower level. We assume excavation for the building will have a maximum cut depth of one level, about l0 feet below the existing ground surface. For the purpose of our analysis, foundation loadings for the structure were assumed to be relatively light and typical ofthe proposed type ofconstruction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the ¡ecommendations contained in this report. SITE CONDITIONS The property was vacant at the time of our field exploration and appeared in a relatively natural condition except for the south end which contains road embankment fill and utilities from the H.PIKUMAR Project No. 17-7-697 -2- subdivision development. Vegetation consists of sage brush, grass and weeds with a stand of scrub oak in the western side of the lot. The site is located on a northeast facing hillside. The ground surface slopes down to the northeast at a grade of about 10 to 15 percent in the building area. Scattered basalt c.obbles and boulders are visible on the surface in the project area. GEOLOGIC CONDITIONS Lot 45 is located near the lower limit of a mapped, very large, dormant landslide complex. Hepworth-Pawlak Geotechnical, Inc. evaluated the overall stability of the landslide as part of the subdivision approval by Garfield County in 1999. The evaluation included depth to bedrock and depth to groundwater level, both being relatively deep. The conclusion was that the landslide complex was not near critical stability condition and moderate cut and filt depths made for subdivision infrastructure and individual lot development should not affect the overall stability of the landslide, We are not aware of any landslide related movements since the subdivision development. FIELD EXPLORATION The field exploration for the project was conducted on September 20,2017. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. 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-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 arc shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engirreer and testing. SUBSURFACE CONDITIONS Graphic lugs of the subsurface condltlons encÒuntered at the site are shown on Figure 2. The subsoils, below about I to 2 feet oftnpsoil, consist ofabout 13 to 20 feet ofvery stiffto hard, H-PÈKUMAR Project No. 17-7-697 -3- sandy clay with likely scattered gravel overlying mixed gravel and clay with basalt cobbles and probable boulders to the boring depths of 22 and 31 feet. Drilling in the underlying coarse granular soils with auger equipment was difficult due to cobbles and boulders and drilling refusal was encountered in Boring 2. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and finer than sand size gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples of the clay soils, presented on Figures 4 through 7, indicate low compressibility under existing moisture conditions and light loading with generally low to high expansion potential when wetted. The clay sample from Boring 2 at 2Vzfeet showed a minor collapse potential (settlement under constant load) when wetted. The laboratory testing is summarized in Table L No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist. FOTINDATION BEARING CONDITIONS The clay soils encountered at typical shallow foundation depth have a moderate bearing capacity and variable settlement/heave potential. A shallow foundation placed on the clay soils could have a risk of post-construction movement potential mainly if the bearing soils are wetted. It will be critical to the long term performance of the structure that the recommendations for surface grading and subsurface drainage contained in this report be followed. The amount of settlement/heave will mainly be related to the depth and extent of subsurface wetting. Partial excavation of expansive clay soils encountered at both borings could be needed to help limit the movement potential and should be further evaluated at the time of excavation. An alternate low movement risk foundation would be to use drilled piers or piles that extend down into the rocky soils encountered at depths of about 15 to 21 feet in the borings. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, the building can be founded with spread footings bearing on structural H.P*KUIVIAR Projecl No. 17-7-697 -4- fill placed on the natural clay soils with a risk of movement. The expansive clay soils should be sub-excavated and replaced with compacted, imported structural fîll to a depth of at leâst 3 feet below bearing level. If a deep foundation is desired to limit potential movements, we should be contacted for additional recommendations. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on at least 3 feet of compacted structural fill should be designed for an allowable bearing pressure of 2,500 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about I inch or less. Additional differential movement up to about 1 inch could occur tlepentling on the wetted depth of 10 feet or less. Unexpected deeper wetting could result in greater movement potential. If these pofential movements are not tolerable, a drilled pier foundation should be used. 2) The footings should have a minimum width of 16 inches for continuous walls antl 2 feet for isolated pads. 3) 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 16 inches below exterior grade is typically used in this area. 4) Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least !4 feet. Foundation walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining W'alls" section of this report. 5) The topsoil and any loose or disturbed soils should be removed in footing areas down to the firm natural soils. Expansive clay soils should then be removed to at least 3 feet below footing bearing level and replaced with structural fîll such as CDOT Class 6 base course compacted to at least 987o of standard Proctor density. The exposecl soils in footing area should be moistened and compacted prior to placing structural fill. The structural fill should extend beyond the fnoring edges at least 2feet. H-PVKUMAR Proiect No. l7-7-697 -5- A representative of the geotechnical engineer should evaluate structural fill for compaction during its placement and observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 60 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 50 pcf for backfill consisting of the on-site soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures suchês adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90Vo of the maximum standard Proctor density at a moisture content slightly above optimum. Backfill placed in pavement and walkway areas should be compacted to at least957io of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the 6) H.PÈKUMAR Project No. 17-7-697 -6- sides of the footings can be calculated using an equivalent tluid unit weight of 300 pcf. The coefficient of friction and passive pressurc values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to rcsist lateral loads should be compacted to at least 957o of tbe maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade construction with a risk of movement. The clay soils exhibit expansion potential and could heave the floor slab if they are wetted and should be sub-excavated at least 2 feet and replaced with compacted structural fill. It is also conìmon where there are expansive soils to r¡se a structural floor ahove crawlspace to limit pote.ntial floor movements rvhich is typically used in living areas. To reduce the effects of some differential movement, floor slabs where used should be separated from all bearing walls and columns with expansion joints which allow unrestrainecl vertical movement. Interior, non-load bearing walls should also be provided with a slip joint at the bottom to allow for at least l7z inches offloor slab heave. 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 at least 507o retained on the No. 4 sieve and less than Zvo 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 should consist of imported granular soils such as CDOT Class 6 road base. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in mountainous areas and whcrc clay soils are present that local perched groundwater can develup during times of heavy precipitation or seasonol runoff. Frozen ground during spring runoff can create a perched condition. Vy'e recommend below-grade construction, such as retaining walls, H-PÈKUMAR Project No. '17-7-697 -7- crawlspace and 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 walt 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 minimuml{zo 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 than 507o passing the No.4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least LVz feet deep. STTE GRADING The risk of construction-induced slope instability at the site appears low provided cut and fill depths are limited. We assume the cut depths for the basement level will not exceed one level, about 10 to 12 feet. Fills should be limited to about 8 to 10 feet deep. Embankment fills should be compacted to at least 957o of the maximum standard Proctor density near optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing all vegetation and topsoil and compacting to at least 95Vo of the maximum standard Proctor density. The fill should be benched into slopes that exceed ZOVo grade. Permanent unretained cut and fill slopes should be graded at 2 horizontal to I vertical or flatter and protected against erosion by revegetation or other means. The risk of slope instability will be increased if seepage is encountered in cuts and flatter slopes may be necessary. If seepage is encountered in permanent cuts, an investigation should be conducted to determine if the seepage will adversely affect the cut stability. This office should review site grading plans for rhe projecr prior to construction. SURFACE 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 and underslab areas should be avoided during construction. H.PVKUMAR Project No. 17-7-697 -8- 2)Exterior backfìll should be adjusted to near optimum moisture and compacted to at least 957a of the maximum standard Proctor density in pavement and slab areas and to at least 907o of the maximum standard Proctor density in landscape areas. The ground surfacc 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 10 feet in paved areas. Free-draining wall backfill should be covered with filter fabric and capped with about 2 feet of rhe on-site soils to reduce surface water infiltration. Roof downspouts and drains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy inigation should be located at least 10 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. 3) 4) 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 warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings drilled at the locations indicated on Figure l, 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 perf'ormed. 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 intcrprctations by others of our infomntiou. As the prujeut evolves, we should provide continued consultation and fielcl services during construction to review and 5) H-PùKUMAR Project No. 17-7-697 -9- 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 ofexcavations and foundation bearing strata and testing ofstructural fill by a representative of the geotechnical engineer. Respectfully Submitted, H-PtKUMAR Steven L. Pawlak, P Reviewed by: Dan P.E SLP/kac H.PVKUMAR Project No. 17-7-697 ;: :ì i.j :, :i il 1 h{ f oÀãirì¡a!z, II q o BENCHMARK: SEWER ¡¡ÀtnOlE .RlM EL. = 100' ASSUMED äfi=r',.rlF.riï v- #'i. f"f !æ,; ¿ Rrltc !i I- t * a 'fi Þ :l t f t"*= a-- *1 t {3 3 ! ahn*- ,,rfiñT r.l , #,ì If ê .}?: 'tì I i Ë ft TYtf'r t'I t i',,r {4 üi ,Dir I .å mt¡ri 25A2550 ÀPPRÔXIMÀTT qCAI F_TFF'f 17 *7 -697 H-PryKUMAR LOCATION OF IXPLORATORY BORINGs Fi-o. 1 BORING 1 EL. 1 I 1.5' BORING 2 EL. 104.5' 115 115 110 110 11 /12 105 36/ 12 !YC= 10.3 DD= 1 20 105 28/ 12 14/ 12 WC=8.3 DD=95 t-l¡J L¡ll! Iz.It-- l¡,J LJ 100 100 Ft!l!1! Iz,o F f¡JJ Li, 20/12 95 47/12 WC=13.0 DD=1 t6 95 32/12 WC= l2.f DÐ=112 90 18/6,5a/4 WC=12.9 DD=l16 -200=93 90 27 /12 \'lC=12,7 DD='l 13 -200=67 50/ 4 8s 85 18/6,40/5 47/12 80 80 17 -7 -697 H-PVKUMAR LOGS OF EXPLORATORY BORINGS Fig. 2 I E ? ; LEGEND TOPSOIL; ORGANIC SANDY SILTY CLAY, F|RM, MOIST, DARK BROWN. 9!.IY.-(9!)i I4'!q!, VERY STIFF TO HARD, SLIGHTLY MOIST, BROWN, MEDIUM PLASTICIÏY,SLIGHTLY CALCAREOUS. 9låY:!.lfl.-c_LAY (g_ç-g!)i ,s¡Ngy1 coBBLEs,_ posstBlE BoULDERS, DENsE/vERy sTtFF,SLIGHTLY MOIST, MIXED BROWN, SASALT ANO 'SITOSTONE ROCK. RELATIVELY uNDlsruRBED DRtvE SAMpLE; 2-tNCH t.D. cALtFoRNtA LTNER sAMpLE. 1 1/12 PXIvLEN;g!'-.i'-.1.'Ê'#'liåi?J?å'iã i#J"irF'3Lì,3å-â LXä?H*?,*,î,TU[S. I enlcrrcll AUGER REFUsAL. NOTES 1r40) N n w F 2. 3. 4. 5. 6. 7. THE EXPLORATORY BORINGS WERT ORILLED ON SEPTEMBER 20,2017 WITH À 4-INCH DIAMETTRCONTINUOUS FLIGHT POWËR AUGER. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASUREÐ APPROXIMATELY BY PACINGFROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFERTO THE BENCHMARK ON FIG. I. THE EXPLORÂTORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATEONLY TO THE DEGREE IMPLIED BY THE METHOD USED. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THEAPPROXIMATE BOUNDARIES BETwEEN MATERTAL Typrs AND rHE rnÀñsrrroHs u¡1 eÈ cRloLiÃ1. GROUNDWATER WAS NOT ENCOUNTEREO IN THE BORINGS AT THE TIME OF DRILLING. LABORATORY TEST RESULTS:wc = WATER CONTENT (%) (ASTM o zzro);DD = DRY DENSITY (PCf) (ASTM D ZZIA):- -200= PERCENTAGE PASSTNG NO. 200 STEVE (ASTM D 17 -7 *697 H-PryKUMAR LËGEND AND NOTES Fig. 3 SAMPLE OF: Sondy Cloy FROM:Boringl@5' WC = 1O.3 %, DD = 120 pcl \\ I,4- 1 ! , EXPANSION UNDER CONSTANT PRESSURE UPON WETTING t I I \¡ rÈd. br olut.PPlt ont b ú.úhÞld t.dd. ñ6 l..li¡c r6Fd ¡hol¡ not b ñpßd!Êd, ã..Þt ,nfùf, ritoú b! r¡fiãn lptrmt .t Kcnor ond kcl¡tE, Inc. Sr?ll Canælldotloñ l.llng p6lomd lnocsdıÉ. *iU & D-4518- 5 4 ñ JJl¡l =an I zotr o Jovtzo() 3 2 1 0 -1 -2 1 t.0 0 t00 17 -7 -697 H-PryKUMAR SWILL-CONSOLIDATION TIST RTSULTS Fig. 4 ¡ SAMPLE OF: Sondy Cloy FROM: Borlng t @ 15' WC = 13.0 "Á, DD = 1 16 pcf 2 ìs JJl¡l =tt1 I zotr ê =o(nzo(J 1 o -1 -2 -5 t.0 t-. EXPANSION UNDER CONSTANT PRESSURE UPON WETTING I F\- I )- , I 1 I rñü. cn nrur o¡Þy oñt b ù.&mtla tdd. lì. b.t¡ñc r.FdrþU not b n¡duê.4 æ.Þl int!ll, iüoul |fi. rrltl$ ô!frñt ot X0mor cñd leciot6, l^c. Srlllhrdldotlon t.dlñg ldomd l¡d.nc. *ft SU L4546. 17 -7 -697 I.I-PryKUMAR SWELL-CONSOLIDATION TEST RESULTS Fis. 5 xj()3qoU'(rs':oäoProoqJo)AIàllËogNıtnı'. C o\oãrl¡¡¡o€d+lUlu-=l_ZUôlñfr,h) æ.2.f.F.¿t-u8ã=drPã8Ebo¿oc) [¡,ô(:<2.ÞI¿., ^!ooôUÈÀc\¡It+(O0OÕll'îrt3¡^s - NolrvorlosNoJNI{IN(f(z)r\o¡(.oIl\INu-)V-¿¿o-I-IUIt-J=tnt4JÉt--V'l¡Jt--z.of-c)Jc)V'z.o()IJJLrJ=an(.oCt)l! SAMPLE OF: Sondy Cloy FROM: Boring 2 @ 10' WC = 12.1 7", ÐÐ = 112 pcl N JJ l¡,1 =Ø I zo F o3ov,zo(J 2 1 0 1 2 - XSF I EXPANSION UNDER CONSTANT PRESSURE UPON WETTING ,7 \) \ ftd. bd nrùlL opt onlr b û¡þmplu tdd. û. bünq r.FÉ rhqll ñot h ñpEducd. dc!¡t lnrull. r¡üoul tì. rrltø oÐrffil olúnor ond bcìol*, lnÊ, Srcllbñdldollon l.dìnq tdomd ln !.Êod6ñ€6 rlh ¡fl D-4S. 17-7 -697 H-PryKUMAR SWTLL"CONSOLIDATION TEST RESULTS Fis. 7 H-PVKUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProjectNo. I7-7-697SOILTYPÊSandy ClaySandy ClaySlightly Sandy ClaySlightly Organic SandyClaySandy ClaySandy Clay with GravelUNCONFINEDCOMPRESSIVESTRENGTHfPSFIATTERBERG LIMITSGRAVELSANDPERCENTPASSINGNO.200SIEVELIQUIDLIMIÏPLASTICINDEX(vù(V'l9367NATURALMOISTURECONTENTNATURALDRYDENSlTYna1161169511211310.313.01,2.98.312112.7BORINGDEPTHI51520'tt/L/2I0I52