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Home My WebLink AboutSubsoil Study for Foundation Design 06.30.17H.PVKUMAR 5020 County Road 154 Glenwood Springs, C0 81601 Phone: (970) 945-i988 Fax: (970) 945-8454 Email: hpkglenwood@kumarusa,com Geotechnical Engineering I Engineering Geology Materials Testing I Environmental Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 62, FILING 2, PINYON MESA TBD PAINTBRUSH \ryAY GARFIELD COUNTY, COLORADO PROJECT NO. 17-7-388 JUNE 3O,2OI7 PREPARED FOR: INTEGRATED MOUNTAIN DEVELOPMENT, INC.. ATTN: JIM GORNICK P.O. BOX 908 GLENWOOD SPRINGS, COLORADO 81602 @ RECEIVBD i¡ov 2 7 t0l7 GARFIELD COUNTY ]MIJIUNITY DEVELOPMENT TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SME CONDITIONS SUBSIDENCE POTENTIAL............ FIELD EXPLORATION SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS FOUNDATION AND RETAINING V/ALLS 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 1 I a _') _ -3- a-J ,,,..,.'','..'.','..- 4 .'......,......'..'. - 4 .................... - 5 .................... - 6 _'7 ...,'..'..''.'.'''.. - 8 -8- H.P\KUMAR Project No. 17-7-388 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at Lot 62, Filing 2, Pinyon Mesa, TBD Paintbrush Way, Garfield County, Colorado. The project site is shown on Figule 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 Integrated Mountain Development, Inc. dated May 1I,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 foundation types, depths and allowable pressut'es 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 two-stoly structure above a basement and with an attached gange. Basement and garage floors will be slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 10 feet. 'We assume relatively light foundation loadings, typical of the proposed type of construction. If building 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 Thc propcrty is rracant ond vegetatecl r,vith sago bnrsh, grass ancl rveorlç, Vegetation in the front part of the lot has been removed duling the subdivision development. The ground surface in the H-PÈKUMAR Projeci No. 17-7-388 a-L- building envelope is relatively flat with a slight slope down to the west. The building envelope is about 4 feetbelow the roadway grade. A deep gully is located in the rear of the lot beyond the building envelope line. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the Pinyon Mesa Development. These rocks are a sequence of gypsiferious shale, fine-grained sandstone/siltstone and limestone with some massive beds of gypsum. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the property. Dissoiution of the gypsum under ceftain conditions can cause sinkholes to develop and can produce aleas of localized subsidence. During previous work in the area, sinkholes have been observed scattered throughout the lowel Roaring Fork River valley. No evidence of subsidence or sinkholes was observed on the property or encountered in the subsurface materials, however, the exploratory boring was relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The lisk of future ground subsidence at the site throughout the service life of the proposed sttttcture, in our opinion is low, however the owner should be aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted, FIELD EXPLORATION The field exploration for the project was conducted on May 16, 2017. One exploratory boring was drilled at the location shown on Figure 1 to evaluate the 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 a 2 inch LD. spoon sampler. The sampler was driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This H-P\KUMAR Project No. 17-7-388 -3- test is similar to the standard penetration test described by ASTM Method D-1586. The penelration resistance values ars an indication of the relative density or consistency of the subsoils. Depths at which the sarnples wele 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 ploject engineer and testing SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The subsoils, below about 6 inches of topsoil, consist of sandy clay to 1 1 feet and sandy silt and clay to 22 feet underlain by meclium dense, silty to very silty sand and gravel with silt zones. The deeper gravelly soils ale possibly weathered formation rock but are logged as soil from a foundation support viewpoint. Laboratory testing performed on samples obtained from the boring included natulal moisture content and density and percent finer than sand size gradation analyses. Results of swell- consolidation testing performed on relatively undisturbed drive samples, presented on Figure 3, indicate low to moderate complessibility under conditions of loading and wetting with a minol to low collapse potential (settlement under constant load) when wetted. The laboratoly testing is summarized in Table 1. No free water was encountered in the boring at the time of drilling or when checked on June 15, 2017 and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The upper sandy clay soils encountered at typical shallow foundation depth and the underlying sandy silt and clay soils mainly tend to settle when they become wetted. A shallow foundation placed on these soils will have a risk of settlement if the they become wetted and care should be taken in the surface and subsurface drainage around the house to prevent the soils from becoming wet. It will be critical to the long-term performance of the structure that the H-PIKUMAR Project No. 17-7-388 -4- recommendations for surface grading and subsurface clrainage contained in this lepolt be followed. The amouut of settlemeut, if the bealing soils becolre wet, will rnainly be rela[ed t-o the depth and extent of subsurface wetting. We expect initial settlements will be less than 1 inch. Wetting of the shallow soils could result in additional settlements of I to 2 inches which would tikely cause building distress. Mitigation methods such as a deep foundation (piles or piers extending down at least 30 feet below existing ground sulface) or lemoving ancl replacing the bearing soils as compacted structural fill should be used to support the proposed house with a lower risk of settlement. If a deep foundation is desired, we should be contacted to provide additional design recommendations. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the natule of the proposed construction, the building can be founded with spread footings bearing on compacted structural fill. The design and construction criteda presented below should be observed fol a spread footing foundation system. 1) Footings placed on compacted structural fill should be designed for an allowable bealing pressure of 1,200 psf. The basement and garage footing areas should be sub-excavated down about 6 to 10 feet below existing ground sulface and the excavated soil replaced with compacted structural fill back to design grade. The sub-excavated areas should extend down at least 3 feet below the footing bearing level. Based on experience, we expect initial settlement of footings designed and constn¡cted as discussed in this section will be about 1 inch or less. Additional settlements of about Vz to I inch could occul if the bearing soils are wetted. A % increase in the allowable bearing pressure can be taken for toe pressure of eccentrically loaded (retaining wall) footings. H-P\KUMAR Project No. 17-7-388 -5- 2)The footings shouid 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 offoundations at least 36 inches below exterior grade is typically used in this area. Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 feet. The foundation should be configured in a box like shape to help resist differential movements. Foundation walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining'Walls" section of this repolt. The topsoil, sub-excavation depth and any loose or distulbed soils should be removed below the foundation area. The exposed soils in footing areas after sub- excavation should then be moistened and compacted. Structural fill should consist of low permeable soil (such as the on-site sandy clay and silt soils compacted to at least 987o of standald Proctor density within 2To of optimum moisture content. The structural fill should extend laterally beyond the footing edges equal to at least Vz the fill depth below the footing. A representative of the geotechnical engineer should evaluate the fill placement for compaction and observe all footing excavations prior to concrete placement. 3) 4) FOUNDATION AND RETAINING V/ALLS 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 55 pcf for backfill consisting of the on-site fine-grained 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 45 pcf for backfill consisting of the on-site fine-grained soils. s) 6) H-PÈKUMAR Project No. 17-7-388 -6- All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressltres such as adjacent footings, traffic, constrttction 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 strLrcture. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts ancl compacted to at least 90Vo of the maximum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least 957o of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment neal the wall, since this could cause excessive lateral pÍessure 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 ealth pressttre 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 sides of the footings can be calculated using an equivalent fluid unit weight of 325 pcf. The coefficient of friction and passive pressure 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 resist lateral loads should be compacted to at least 95Vo of the 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 settlement risk similar to the foundation if the underlying soils are wetted. H-P\KUMAR Project No.'17-7-388 7- To reduce the effects of somc diffcrcntial movement, floot slabs should be sepalatcd 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 requilements 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 Iess than 2Vo passing the No. 200 sieve. All fill 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 soils devoid of vegetation and topsoil. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, 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 seasonal lunoff. Frozen ground during spring runoff can create a perched condition. We recommend below-grade construction, such as retaining walls and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. An underdrain should not be provided around slab-at-grade garage and crawlspace areas to help limit potential wetting of bearing soils from shallow water sources. The drains should consist of drainpipe placed in the bottom of the wall backfill surounded 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 zidjacent finish grade and sloped at a minimum IVo to a suitable gravity outlet or sump and pump. Free-draining granular material used in the underdrain system shor"rld contain less than ZVo 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 Ieast lVz feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. H-PÈKUMAR Project No. 17-7-388 -8- 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. 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 90Vo of the maximum standard Proctor density in landscape areas. 3) The ground surface 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 backfiil should be covered with filter fabric and capped with at least 2 feet of the on-site soils to reduce surface water infiltration. 4) Roof downsponts and drains should discharge well beyond the limits of all backfill. Graded surface swales should have a minimum slope o137o. 5) Landscaping which requires regular heavy irrigation 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 irrigation. LIMITATIONS This study has been conductecl in accordance with generally accepted geotechnical engineering principles and practices in this arca at the time of this study. We make no wananty either' express or implied. The conclusions and recommendations submitted in this report 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, preventioh 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 H-PVKUMAR Project No. 17-7-388 -9 - 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 fi'om those described in this report, we should be notified so that re-evaluation of the recommendations may be made. This leport has been prepared for the exclusive use by our client for design pulposes. 'We are not responsible for technical interpletations by others of our infolmation. As the ploject 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 interpleted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. We recommend on-site observation of excavations ancl foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, H-PÈ KU Louis E. Eller' Reviewed by: Steven L. Pawlak, P.E. LEE/ksw cc:Oddo Engineering - B H-PÈKUMAR Project No. 17-7-388 T LOT 62 BORING 1 a LOT 63 LOT 61 J I I I J -¿--'-------e- - -- -J---l_--ì--- PAINTBRUSH WAY 1 APPROXIMATE SCALE-FEET 17 -7 -388 H.PryKUMAR LOCATION OF TXPLORATORY BORING Fig. 1 gORING I EL.6193,7' LEGEND 0 ñ n n t% frl h I loPsolt; oRcANlc 5ANDY SlLf AND CLÄY, SLICHILY l¡0lST, BRoWN. 47 /12 crÂY (cL); PLÄsIlctTY, SILIY, SANDY. SÍIFF TO VTRY SfII', sLIGNTLY MOISI, BROWN, LOIV CALCARTOUS IRACES. 1o/12 WC:5.3 cLÂY ÁND S|LT (Ct-ilt"); SANDY, VERY SftFF, SLtCHlty MOtSt, LrcHt BRoWN, CÀLCARTOUS, SOIJE GYPSUM. SAND ÂN0 cRAvEL (sM-oM); srLly to vrRy stlry, sol¡tE GRAvEtLy stLT zoNrs, M€OIUM DTNSE. SLIGHILY IJOISI, MIXIO 8ROWN. SILTSÍONE TRÁCI¡TNIS. DRIVÊ SAMPLE, z-INCH I.O. CÁLIFORNIA LINER SAMPLT. D0"102 10 26/12 ¡:rrr DRIVE SÂMPIE BLoIV CoUNÍ. INoICATES lHÀl 17 8t0WS 0F Á 110-P0UN0 HAI'IMER"" '' rÀ[LrNc ¡0 fNcHEs wERt RtoutRto to oRtvt THt sÁMpttR t2 tNcHEs. 21/12 WC=1.3 00=99 -200=79 ,^ NOTES I. 'IHT EXPTORAIORY SORING WAS DRII-LIO ON IIÁY 16,2017 WTH Ä 4.INCH DIÂMEIER CONÍINUOUS fLIGHT PO',YER ÁUGIR. 22/12 WC=3.d 2. THT LOCATION OF IHT EXPLORÀTORY BORING WAS MEASURED APPROXIMÁÍTLY BY PACING ÍROM FIÂIURTS SHOI¡/N ON THT SIÍT PI-ÄN PROVII)ED.DD=1 04 3. fHE TTTVATIOI{ OF IHE EXPLORAÍORY EORING WÂS MEÁSUREO ST HÀNO I.TVEL ÁNO RETÉfis TO GRÄDE SIAKE EI€VÀTION ON PÁINT ERUSH I¡TÂY. 5?/12 WC=3.3 4. THE EXPTORAÏORY SORING LOCAIION ÄNO ELEVÀIION SHOULO SE CONSIOERTO ÂCCURATE ONLY fO ÌHE OECRÊE IMPLIEI] BY IHE METHOD USTD. 00=12s 5. fHI LINES BETITEEN IIAIERIALs SHOl|lN ON THT EXPLORAIORY BORINC LOC REPRESENT THE APPROXIIJÁÏT SOUNDARITS BTIIYETN MATERIÄL IYPTS AND THI TRÀNSITIONS MÅY BE CRAI)UAL, 6. CROUNDVIÂI€R WÁS NOI ENCOUNTEREO IN TH€ BORINC ÂT fHE IIMI OF DRILI.ING. 7. TÂBORATORY ÍIST RESULTS: Wc = vlAÍER coNIENf (,¿) (ÂsTM 0 22f6): DD = oRY o€NsllY (pcf) (ÀsT}r 0 2216); -200 = PtRctNTACt PÄSS|NC N0. 200 SttVE (ASTM 0 il40). 50 5s/12 J5 40 s3/12 WC=2.7 D0=l l5 -2o0=62 45 50 81/12 55 N o L c5z. oo Éots ÉoJÈxu o ØUts()z oz ôz (JUJ dI u ¿¿ÈI 6æ rO IÈ- IN E: 6 r SAMPLE OF: Sondy Silly Cloy FROM:Boringl@5' WC = 5.3 %, DD = 102 pcf ADDIÏIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING { às ) -Jt¡J =tn I zotr É)loØzo() àe J)t! =tn I z.otr ê =o U1zoO 1 0 -1 -2 -3 -4 1 0 -t -2 -3 -4 -5 1.0 APPLIED PRESSURE - KSF RE- 10 f00 SAMPLE OF: Sondy Silt ond Cloy FROM:Boringl@20' WC = 5.4 %, DD = 104 pcf ADDITIONAL COMPRESSION UNDTR CONSTANT PRESSURE DUE TO WTTTIUC ---"-- L '''1 n.r. lclt r.lulb opplt ont lo b. þmÞh¡ t.¡tcd, l¡. t.ling ñport lholl not bn Fprcduc.d. lx€pt in rull, rftout ü. rrltt.ñ oppdol of <umor ond kFíqt.¡. lnc. Srrll lonsolidst¡on tEsting Ffoñld ln rccoddnc! ith m 0-66. 17 -7 -388 H-PryKUMAR SWELL-CONSOLIDATION TEST RESULTS Fis. 5 H.P*IruMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 17-7-388 .SAMPLE LOCATIONNATURALMOISTURECONTENTNATURALDRYDENSITYGRADATIONATTERBERG LIMITSUNCONFINEDCOMPRESSIVESTRENGTHGRAVELSAND(%\PERCENTPASSINGNO.200SIEVELIQUIDLIMITPLASTICINDEXSOIL TYPEBORINGDEPTH(%t55.3t02Sandy Silty Ciay154.39979Sandy Siit and Clay203.4104Sandy Silt and Clay25J.J125Very Silty Sand withGravel402.711562Gravelly Sand and Silt