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Home My WebLink AboutSubsoil Study for Foundation Design 06.24.2021rlftcnar,& rlçsûGidc$ llm. " Geoeahnrc¡il and rMatetlials Er,gineers ar¡d lEnúir.onÍnerüül $ciie¡'if i$ts SCIZ0C,oumgRoad il5'41 Glmrwood,$¡Nrmge.,C() I il60[ ¡ftome: i(970) 945-7988 tux.t('9V{x)945&45t4 ermiai[: nia,gfiemmøood@tummusa.,ooma www.kurnarusa. comAn fufr¡f¡c ûrr¡cd Aoûtpff'y $ñise ll¡oodims: iDe¡nvm iG[Q), ]Fa&m, {}dlondo $pnings, Fc,ntt .cc$,I,ì¡rs, Glem*iocrd ;Sþirys, mil ÍSnmmiit Ooruúy,, 'Onil'oadlo Jluu¡'e 24,2021 Red House Architecture Attn: Bruce Barth 815 Blake Avenue Glenwood Springs, Colorado 81601 bruceØredhousearchitecture. com Project No. 2l-7-455 Subject: Subsoil Study for Foundation Design and Septic Disposal Soils, Proposed Residence, Lot RR3, Filing 8, Elk Springs, 620 Juniper Drive, Garfield County, Colorado Gentlemen: As requested, Kumar & Associates, Inc. performed a subsoil study for foundation design and septic disposal soils at the subject site. The study was conducted in general accordarice with our agreement for geotechnical engineering services to Red House Architecture dated ìll4ay 13,202I Subsoil evaluation in the proposed septic disposal area was added to our scope of services. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Evaluation ofpotential geologic hazard impacts on the site are beyond the scope of this study. Proposed Construction: The proposed residence will be a one- and two-story wood-frame structure with detached garage located on the site as shown on Figure 1 Ground floors are assumed to be structural over crawlspace or slab-on-grade. Cut depths are expected to range between about 2 to 5 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. The septic disposal area is proposed to be located southeast ofthe proposed residence. If building conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presetrted in this report. Site Conditions: The subject site was vacant at the time of our field exploration. The ground surf'ace was sloping down to the south/southeast at a grade of around I 0 to 1 5 percent in the proposed building area. The overall terrain is variable with moderately steep hillsidc slopes northeast and southwest of the building area. Vegetation consists of grass and sagebrush wrth Juruper and pinyon trees outside of the building area. Basalt cobbles and boulders were present on the surface in the steeper sloping lot areas. ., Subsidence Potential: The Elk Springs subdivision is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution and plastic flow of the evaporite can Çause sinkholes to develop, localized subsidence and ground faults. During the geologic assessment for the subdivision development, linear faults were identified along the southwest perimeter of the proposed development which appear to cross through the proposed building site of Lot RR3. The two faults are separated by a graben which was formed by ground subsidence and more recently infilled by alluvial deposited soil. The faults appear to be associated with evaporito flow deformation. It is uncertain if this deformation is still an active geologic process or if deformation has stopped. To our knowledge, there have not been reported ground fault problems with gypsum deformation in the Roaring Fork valley in areas underlain by Eagle Valley Evaporite. If broad regional gypsum deformation is still occurring, it is likely the deformation is at a very slow rate and should not be a potential hazwd. Based on our present knowledge of the site, it cannot be said for certain that ground movement and sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot RR3 is low and similar to other lots in the area but the owner should be aware of the potential for ground movement and sinkhole development. Differential fault creep if occurring at the site, would tend to be localized along the fault escarpments (the transition to steep uphill and do'¡¡nhill slopes) Because of this, we recommend the building not be located across these faults. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits in the building area and two profile pits in the designated septic disposal area at the approximate locations shown on Figure l. The logs of the pits are presented on Figure 2. The subsoils encountered, below about I foot of topsoil, consist of silty sandy clay. Basalt boulclers were encountered in Profile Pit I below about 5 feet. Results of swell-consolidation testing performed on a relatively undisturbed sample of sandy silty clay, presented on Figure 4, inciicate iow compressibiiity uncier existing iow moisture conciition anci iight ioaciing, a iow collapse potential u¡hen wetted under constant light loading and moderate to high compressibility potential under increased loading. The laboratory test results are summarizedinTable 1. No free water was observed in the pits at the time of excavation and the soils were slightly moist to moist. X'oundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, spread footings placed on the undisturbed natural soil designed for an allowable bearing pressure of 1,500 psf can be used for support of the proposed residence. The soils tend to colnpress after wetting under load and there could bc somc post-construction foundation scttlement. Continuous footings and foundation f(umar & Aseoci&s, Fms. o PrqúÞd ltlo- 21-7'155 aJ- walls are preferred over isolated pads to better resist differential settlement and limit building distress. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. The topsoil and loose disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended dorm to the undisturbed natwal soils. The exposed natural soils should be moisture conditioned to near optimum and compacted to at least 95 percent of maximum standard proctor density. We should observe the completed foundation excavation prior to forming footings to confirm suitable bearing conditions. Exterior footings should be provided with adequate æver above their bearing elevations for frost protection. Placement of footings at least 36 inches belowthe 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. 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 55 pcf for the on-site soil as backfill, excluding organics and rock larger than 6 inches. X'loor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade 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 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 relatively well graded sand and gravel, such as road base, should be placed beneath slabs for subgrade support. This material should consist of minus Z-inch aggregate with less than 5AYo passing the No. 4 sieve and less than l2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least95Yo 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. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the area and r¡¡here clay soils are present that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. We recommend below-grade construction, such as retaining walls, 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 wall backfill surrounded above the invert level with free-draining granular material. The drain should be placed at each level of l{r¡r¡rar I Åssosiates, [nc. io F,roidNo'2I-741i5 -4- excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum 17ó to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2o/opassingthe 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 least lYz 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. Sur{ace Drainage: Providing proper surface drainage will be critical to the long-term performance of the residence. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation of the 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 95%o 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 covered with filter fabric and capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. 3) The ground surface surounding 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 l0 fcct in unpaved areas and a minimum slope of 3 inches in the first 10 feet in pavement and walkway areas. 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 l0 feet from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the building caused by irrigation. Septic System Suitability: The USDA gradation testing results presented on Figures 5 and 6, indicate a soil type of 2A (Loam or Silt Loam) for the samples taken from Profile Pits 1 and 2 A civil engineer should design the infiltration septic disposal system. 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 bascd upon the data obtained from the exploratory pits excavated at the locations indicated on Figure 1, the proposed type of construction and our expericncc in thc arca. Our services do not include dctcrmining the presence, prevention or possibility of mold or other biological contanrinants |ftnnar &.Àasoollilcs, tnc. 0 tuiætilo"2î-l-{56 5- (MOBQ developir:g in the future. If the client is corrcemed about MOBC, then a profbssional in this special fieid of practice should l:e consultetl. Our findings include inte4rolation and extrapoiation of the subsurfäce conditions ídentifietl at the exploratory pits and variations in the subsurface conciitir:rrs may not become evident until excavation is performetl. If conditions enccuntered during construction appear diffçrent frorn those describeci in tliis report, we should be no¡ified at once so re-evaiuation of the recommenclations mav be made. This leport has beet prepared for the exclusive use by our client for clesigr purposes. We are not responsible for technical interpretations by others of our information. As the prcrject evolves, rve shouid provicle continued consultation artì field services during construction to review and tnonitor the irnplen:entation of our recommendations" and to veriÛ tirat tlie recomrxendations have been appropriately interpreted. Significant design changes may require adclitional analysis or-rnodifications to the reçommenclations presented herein. We recomrnend on-site obselvaticn of excavations ancl foundation bearing stlata and testing of structurai fìI1 by a representative of the geotechnical engineer. lf you have any questions or if we may be oflfurther"assistance, pleasc iet us know. Respectfully Sutrmitted, Kutr¡er CÈ ;'\ix¡r¡ti;r1r"" Ir¡f. Steven L. Pawlak, P Reviewed by: Þ f)aniel E. Hardin, P.E. SLPlkac Attachments: Figure I - Location of Expioratory Pìts Figure 2 -Logs of Expioratory Pits Figure 3 - Legend and Notes Figure 4 - Swell Co¡rsolidation Test Results Figures 5 and 6 - USDA Gradation Test Results Table 1 - Sumrnary of Laboratory Test Resuits 7, <,,1 5222 Kumar & Arsociatec, lnc.'Project N0.21-7-455 -1 ,, -- to JUNIPER DRIVE., n%* .I 2 P IT S¡TEIFLAN t5 U 30 APPROXIMATE SCALE-FEET oNNo ìr-a - P ..a715 21 -7 -455 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1 E ¡ PIT 1 EL. 6724' Pll 2 EL. 6721' PROFILE PIT 1 PROFILE PIT 2 0 0 WC=6.9 DD=94 ¡-t! L¡lL IIt-fL l¡Jâ 5 - WC=6.6'-2oo=84 LL=3 I Pl='l 3 - J WC=6.6I GRAVEL=0 SAND=29 5 SILT=57 CLAY=14 t-t¡J l¡JL Ift--(L tiJôWC= 10.8I GRAVEL=O -l snND=37 SILT=45 CLAY= 1 I -J l0 10 /V9:'/,/ Fig. 2LOGS OF EXPLORATORY PITS21 -7 -455 Kumar & Associates I E ? I T f.EqEtrD ToPSolL; CLAY, SANDY, ORGANICS, MEDIUM STIFF To STIFF, MOIST, MEDIUM BROWN CLAY (CL); SANDY, SILTY, MEDIUM STIFF TO STIFF, MOIST TO SLIGHTLY MOIST, MEDIUM BROWN, SLIGHTLY CALCAREOUS WITH DEPTH, LOW PLASTICITY. CLAY (CL); SANDY, SILTY, SCATTERED BASALT BOULDERS, VERY STIFF, SLIGHTLY MOIST, BROWN, LOW PLASTICITY. F t HAND DRIVEN 2_INCH DIAMETER LINER SAMPLE I I I I DISTURBED BULK SAMPLE. PRACTICAL DIGGING REFUSAL ON A BOULDER. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MAY 18,2421 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND TI{E TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PIÏS AT THE TIME OF EXCAVATION. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7. LABORAÏORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENS|TY (pct) (asrv D 2216): _ZQO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 11AO); GRAVEL = PERCENT RETAINED ON NO. 10 SIEVE; SAND = PERCENT PASSING N0.10 SIEVE AND RETAINED ON N0.525 SIEVE; SILT = PERCENT PASSING NO. 325 SIEVE TO PARTICLE SIZE .002MM; CLAY = PERCENT SMALLER THAN PARTICLE SIZE .002MM. 21-7-455 Kumar & Associates LEGEND AND NOTES Fig.3 F I 1 0 -1 ^-2àq j-s L¡l =U' t_4 z.otr OE Jo U)z.o<J -6 -7 -8 -9 -10 1 1.0 APPLIED 100 SAMPLE OF: Silty Sondy Cloy FROM:Pit1E^2' WC = 6.9 %, ÐÐ = 94 pcf Kumr ond ÆÐcldé, lnc. Ss.ll bnslldoilon t€dñs Fdomd lndæ*ñc. wnh AS D448. i ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE IO WETTING _ -___: t-i i t I :i it : I .li 21 -7 -455 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 02. ?el - rrircftCt,rrrrz-CÐmo-utr=o(oËÕ5-aæ,qaIPERCENT RETAINEDo!ñôôoi-oFmã--tmÐoþ3J3IEorma-f r.)m--lmJJØÀlloç;f2lI=l1elÉ:lËlçlïil_l-T l.=lËi*l;tEFu!JÐmf-OñzoOJ-J\oo\CNr--15('¡\ÔÕ\C)f-co\Ôô\c(nUU)(JÊJ{-!ITT-Oj=-n:D1.ì=-U-Ð@*.tcoTtrTCrrrzro:C]:\\\PERCENT PASSINGf.;'I!IÈUì(-'ìxc3ß)aAo(hînoo.ß,(DÎncLNCG:T,cız-rrLft---.17r¡VtCr--iVtTl(o(¡ t t n HYDROl\/lETER ANALYSIS SIEVE ANALYSIS I I I I / I / I / READINGS U.S, STANDARD it140 #60 #35 CLEAR SOUARE OPENINGS 24HR. /HÊ 1 MIN, #325 #4 3 5'6" B" 045 [ltN. 15 100 '10 00 20 BO 30 70 o t¡Jz.aF l¡J É. l---z. UJOú, l¿Jo- 40 60 (, z. u't(n fL l---z.l¡lOÉ. t¡JL 50 50 40 70 30 g0 20 90 t0 100 0 ,001 .002 .005 .0c9 .019 .0.15 .106 -A25 .500 1.00 2,c0 4.75 9.5 19.0 37.5 76,2 152 243 DIAMETER OF PARTICLES IN MILLIMETERS CLAY ÓBALES GRAVEL O %SAND 29 %SILT 57 %CLAY 14 % USDA SOIL TYPE: Silt Loam FROM: P?-2 @ 4'-4.5' S¡]]V FINÊ FINE MEDIL]I,./ 21 -7 -455 Kumar & Associates USDA GRADATION TEST RESULTS Fig. 6 lGrt[ffiifi*ifffiiiyå*"::TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo, 2l -7.455SOIL TYPESilty Sandy ClaySil5z Sandy ClayLoamSilt LoamPLASTIC INDEX(/"1JIATTERBERG LIìIITSLIQUID LIMIT(%)IJCLAY(:/"18I4ISILT(%)4557SANDf/"'l5t29USDA SOIL TEXTUREGRAVELl'/ù00l'/ùSILT&CLAY6.99484SAND("/ùGRADATIONGRAVEL(/,1NATURALDRì'DENSITY(pcf)NATURATMOISTURECONTENT("/ù6.610.86.6DEPTHttl25to5%7to84to4v,SAIIPI.E LOCATIONPIT12ProfilePit IProfilePit 2