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HomeMy WebLinkAboutSubsoil Study for Foundation Design 02.13.2017H.PVKUMAR 5020 Comty Road 154 Glenwood Spings, C0 81601 Phone: (970) 945-7988 Far (970) 945.8454 Email: hpkglenwood@kumarusa.com Gaolschnlcel Engherfig I Enghcoilrg Gedogy ilblcdalr Tcrhg I Erlllonmental Olfice Localions: Pafier, Glanwood Spilngs, and Summlt Counly, Cdoado February l3,20l7 Heidi Beattic 109 Valley Court Basalt, Colorado 8 162 l-7303 (lrr"iclil:cutt if & :: rnitil.cot tt) $t&CHllV[1Ei JUL 1 ? ?0r7 6ARFI[I,11 COLJi'IiY )MfillilNll} I}F\l[:l 0FiJIN i Project No.l7-7-147 Subject:Subsoil Study for Foundation Design and Percolation Test, Proposed Residence, l-at22, Callicotte Ranch, Garfield County, Colorado Dear Ms. Bcattie: As requested, H-P/Kumar performed a subsoil study and percolation test for foundation and septic disposal dcsigns at the subject site. The study was conducled in accordance with our proposal for geotechnical engineering services to you dated January 25,2O17. The data obtuined and our recommendations based on the proposed construction and subsurface conditions encountered arc presented in this report. Hepworth-Pawlak Geotechnical, Inc. (now H-P/Kumar) previously performed a preliminary geotechnical study for Callicotte Ranch and reported their findings April 19, 2002, Job No, l0l 821. Propored Constructlon: The proposcd residence will be one and two story wood frame construction above a crawlspace or basemenl and with an attuched garage, The house will be located on the site as shown on Figuro L Garage and basement floors will be slabon-grade. Cut depths are expected to range between about 3 to 5 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of cqnstruction. The septic disposal system is proposed to be located downhill and southeast of the house, If buitding conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluale the recommendations presented in this report. Site Conditlons: The property was vacBnt and snow cever was about 18 inches at the lime of our field exploration. Vegctation consists of pinion and juniper forcst in the western portion of the lot and scattered sage brush, grass and weeds in the eastern and southern part of the lot, The ground surface slopes down to the southcast at t grade of l5 to 20 percent in the building area at\ $ \^ -7 - and bccomes less steep below. A natural drainage swale is locnted belorv the septic disposal orea. Subsurface Conditions: The subsurface conditions at the site werc evaluated by excavating two exploratory pits in the building area and two profile pits in the 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 one foot of topsoil, consist of one to three feet of sandy silty clay overlying basalt cobbles and boulders in sand, silt and clay matrix. Results of swell- consolidation testing performed on a relatively undisturbed sample of the matrix soils, presented on Figure 3, indicate low compressibility undEr existing moisture conditions and light loading and a low collapse potential (settlement under constant load) when wetted. The sample was moderately compressible under increased loading after wetting. Results of a gradation analysis performed on a sarnple of silty sandy gravel with cobbles (minus 5 inch fraction) obtained from the site are presented on Figure 4. The laboratory test results are summarizcd in Table I. No free water was observed in the pits at the time of excavation and the soils were slightly moist to moist. Foundation Recommcndations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on the undisturbed natural granular basalt rock soil designcd for an allowablc soil bearing pressure of 2,000 psf for support of the proposed rcsidence. The matrix soils tend to compress after wctting and there could be some posl-construction foundation settlement. Footings should hc a minimum width of 16 inches for continuous walls and 2 fect for columns. l,oose and disturbed soils and sandy silty clay encountEred at thc foundation bearing level within the excavation should be removed and thE footing bearing level extended down to the undisturbed natural granular basalt soils. [t is our experience in the basall rock soils that a conventional large excavalor can dig about 2 feet deeper in a house excavation than the refusul depths encountered in our pirs. Deeper excavations and narrow utility trench excavations may require rock excavation techniques such as chipping or blasting. Exterior footings should be provided rvith adequate cover above their bearing elevations for frost protection. Placement of footings at lesst 42 inches below the exterior grade is typically used in this area. Continuous foundation wnlls should be reinforced top and botlom to span local anomalies such as by assuming an unsupported length of at least l0 feet. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressurc based on an equivalent fluid unit weight of ut lesst 50 pcf for the on-site soil as backfill. Floor $labs: The natural on-site soils, exclusive of topsoil, are suitable to support lighrly loaded slabon-gradc construction. To reduce tte effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joint.s which allow H.PtKUMAR Projecl No 17.7-147 -?- unrestrained vertical movernent. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirernents 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 less than SOVI passing the No. 4 .sieve and less than 27a passing the No. 200 sieve, All fill materials for support of floor slabs should be compacted to at learl9SVo 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 mountainous :ueas that local perched grourtdwater can develop during tirnes of heavy precipitation or seasonal runoff, Frozen ground during spring runoff can also creBte a perched condition. We recommend below-grade construction, such as retaining walls, basements and crawlspace areas, be protected from wetting and hydrostatic pressurc buildup by an underdrain system, The drains should consist of drainpipe placed in the bottom of the wall backfill sunounded 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 slopcd at a minimum l9o to a suitable gravity outlet. Free-draining granular material used in the underdrain systern should contain less than 27c passing the No. 200 sieve, lEss than 507c passing the No. 4 sieve and have a maximum size of 2 inches. The drain gruvel backfill should be at least l/r feet deep. Surface Drainage: The following drainage precautions should be ohserved during construction and maintained at all times after the residence has been compleled: l) lnundation of the foundation excavatiorts and underslab areas should be avoided during construction. 2) Exterior backfill should be adjustcd to near optimum moisture and compacted to at least 95lo 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 capped with about 2 feet of the on-site, finer graded soils to reduce surface water inftltration. 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 l2 inches in the first l0 fcet in unpaved area.s and a minimum slope of 3 inches in the first l0 feet in pavement and walkway areas. A swole may be needed uphill to direct surface runoff around the residence. H-PTKUMAR Prolect No 17-7-147 -4- 4J Roof downspouts and drains should discharge well beyond the limits of all buckfill. Landscaping which requires regrrlnr henvy inigntion shonlrl be located at lenst 5 feet from the building, Consideration should be givcn to the use of xeriscapc to limit potential wetting of soils below tho building caused by irrigation. Percolallon Testing: The soil texture and structure conditions in the proposed septic disposal area were evaluated by excavating two profile pits at the approxirnate locations shown on Figure I and performing percolation testing. The logs of the profile pis are presented on Figure 2. The subsoils encountered consist of topsoil and sandy silty clay overlying basalt cobbles and boulders in a sand, silt and clay matrix. The upper two feet of the granular soil contained less cobbles and boulders. Results of a USDA grodation analysis performed on a samplc of gravelly loamy sand with cobbles (minus 5 inch fraction) obtained from the site are presented on Figurc 5. The soil type based on gradation analysis is 0 due to the rock conteni, No free water or evidence of scasonal perched water was observed in the pits at the time of excavation and the soils were slightly moist to moist. Percolation tests were conducted on February l,2Ol7 to further evaluate the feasibility of an infiltration septic disposal system at the site. Three percolation holes were dug at the locations shown on Figure l. Test holes rvere hand dug at the bottom of shallow backhoe pits aod were soaked with water one day prior to testing. The soils exposed in the percolation holes are similar to those exposed in the Prolile Pits. The tests were conducted in thc granular soils below the topsoil and sandy silty clay soils. The percolation t€st results are presented in Table 2. Based on the subsurface conditions encoun(ered in the profile pits and the percolation test results, the tested area and subsoils should be suitable for a septic disposal system. A civil engineer should design the infiltration scptic disposal sysrcm. Limltations: This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no waffanty either expressed or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory pits excavated al the locations indicated on Figure l, the proposed typE of construction and our experience in the area. Our serviccs do not include determining the presence, prevention or possibility of mold or other biological contominants (MOBC) developing in the future. lf the client is concerncd about MOBC, thcn a professional in this special field of practice should be consulted, Our findings include interpolation and extrapolalion of the subsurface conditions identified at thc exploratory pits ond variations in the subsurface conditions msy not become cvident until excavation is pcrformcd. If conditions encounterEd during construclion appear different from those describcd in this report, we should be notified rt once so re-evaluation of the recommendations may bc made. s) H-PtKt MAll Progect No 17-7-147 -5- 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 informntion. 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 interprcted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. We recommend on-site observation of cxcavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, H-P*KUMAR Eller Reviewed by: (l 4 L : DanielE. Hardin, P.E. LEE/ksw attachments tbof,1 Figure I - Location of Exploratory Pits and Percolation Test Holes Figure 2 - Logs of Exploratory Pits Figure 3 - Swell-Consolidation Test Results Figure 4 - Gradation Test Rssults Figure 5 - USDA Gradation Test Results Table I - Summary of Laboratory Test Results Table 2 - Summary of Percolation Test Results cc:DGP Structural - Don Pettygrove (rlgprgj!*b1qy!:I1,tg1) H-P*KJlvlAll Proiect No. 17.7-147 dls BUILDING SETBACK "s IIt I t PIT 1 PIT 2 PA I PHOFIIEI PIT 1 PA 2 P3 A I PROFILE PIT 2 "s APPROXIMATE SCALE.FEET PROPOSED RESIDENCE 17-7-147 H-PryKUMAR LOCATION OF EXPLORATORY PITS Fig. I PIT I EL. 5688' ?lf 2 EL. 6684' PROFI EL. LT PIT I PROFILE PIT 26579' EL. 6676' 0- blrl I L h-lr,a :! +4=55 -2OO=21 GRAVEL=53 SAIID=32 SILT='l 3 CI.AY=2 I!lrlb- I IFu.tr,it -5 5- - l0 10- LEGENO N ToPSOIL; ORGANIC SANDY slLT AND CLAY' wlTH coBBLEs AND EOULOERS lN BUILOING ARSA, FIRM, MO|5T, DARK 8ROW. CLAY (CL)i SANDY. SILTY. sTlFF, SLIGHTLY MO|ST, REDDISH BBOWN. EASALT C0EBLES ANo EoULDERS (cM)t lN A SAND, slLT AND CLAY MATRlx, DENSE, SLIGHTLY MOIST, LIGHT BROWN, CALCAREOUS, UPPER t' TO 2. LESS ROCKY IN PROFILE PITS. F [_l t HAND ORIVEN LINER SAMPLE. DISTURBED BULK SAMFLL. PRACTICAL OIGGING REFUSAL. NOTES I. THE EXPLORATORY FITS WERE EXCAVATED $/ITH A BACKIIOE ON FEBRUARY 1, 2017, 2. THE LOCAIIONS OF THE EXPLORATORY PITS WERE MEASURED AFPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED AND GPs. 3. THE ELEVATIONS OT THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN CONIOUFS ON THE SITE PI-AN PROVIDEO. 4. THE EXPLORATORY PIT LOCAIIONS AND ELEVATION5 SHOULD BE CONSIDERED ACCURATE ONLY IO THE DECREE IMPLIED EY THE METHOD USED. 5, THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PlT LOCS REPRESENT THE APPROXIMATE SOUNDARIES BETWEEN MATERIAL IYPES AND THE TRANSITIONS MAY Ef GRADUAL. 5, GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATING. PITS WERE BACKFILLED SUBSEOUENT TO SAMPLING. 7. I.ABORATORY TEST RESULTS: WC = WATER GONTENT (r() (ASTM D 22ta)t DD = DRY DENSITY (pcf) (ASTM D 2216); +4 = FER8ENTAGE RETAINED ON NO. 4 SIEVE (ASTM D AZZ)i -200 = PERGENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140); Grovcl = Pcrcsnl relolned on No. lo Slova Sond = Psrtenl posslng No. l0 sleve ond relolncd on No.325 sleveSlll = Pprcanl posslng No. 325 slave to porllclc sl:c .002mm Gloy = Percanl gmqller lhon porllcla slze ,002mm Itl/C=1O.4 DA=77 -200=29 17-7-147 H.PryKUMAR LOGS OF EXPLORATORY PITS Fig. 2 OFt Colonrantm Sllly Olnyny 5o = 10.48, DO = 77 pcl :Borlng2O2' - z9rl COMPRESSION UNOER CONSTANT PRESSURE UPON WETTING t 0 lt j-z lr,-tn r_3 zo F $-ro,hzou-5 17 -7 -147 H-PV(UMAR STVELL.CONSOLIDAIION TEST RESULT Flg. 3 lrcv€ AXlLYstSIlYOFOMEIEF A}IAL SAflO GRAVEL FINI MEOIUM JCOANSE FINE coARS€ t E E t00 a0 t0 ?0 to lo .g !0 t0 t0 , o l9 :o l0 .0 ID t! 30 t! to! i E EI CIAY TO SILT COSBLES cRAVtL 55 X 5Atl0 2l X TIQUID IIMII PLASTICIIY INDEX sAMPlg or: SltU Sondy Ctov.l wllh cobbl.t SILT ANO CI.AY 2,1 Z FROMi Borlng2O3-3.5' fh.r. l.rl ?6ullt oppl, Dnlt lo li. tamplat rhich ra4 tailrd. lht larllnt raFotl tholl ocl ba raprcduc.d..r(rtl ln lsll. ritholl lha rtllla^ opproYgl ol Xgme' | furcCl.l.t, lnc Sl!r. onoltrlt llalliB h pl?lomtd lnoc.ldqita rlrh rsru 0j22. r5rr cl16 and/!, t51U glll0, GRADATION TEST RESULTS Fig. 417 -7 -147 H-PryKUMAR 3t: IIj tI t?:i 71.{R T|MEREA0IN{3g 1 15 MlN, 60MtNtgMtN.4 MtN. U,E. STAAIDARD SEHIES ir60 #alg #18 #10 CLEAR SOUAFE OFENINSS 0 *4 3/4', I 3.5.6.8. o UJz Flrj(r Fzul(J Et!o- l0 20 30 40 50 60 J00 so 80 70 60 50 {0 30 20 10 oz6 u1 o- Fzt!(Jctll 0- r0 80 90 r00 o081 .002 .005 .o{xl ,019 ,(x5 .106 .0?5 500 t-00 ?00 DAMETER OF PARNCLES IN MILUMEIEFS {,75 95 190 375 76.2 152 203 UJ r:{DgUt I COBBLES 33 % GRAVEL 34 OA SILT i3 % USDA SOIL TYPE: Gravelly Loamy $and wilh Cobbles SAND 18% ct-AY 2 % FROM: Prcfile Pit r @ 3-4' --------{-F --------ts-l- ._-l- -#.- t-=--.----H- -::-=F=. -t-.-- t ----f--_-{-- 4 ----..t__ ---l- "...... {----,.- =:-a=-- _t._-__. -{- *. f- *- {-. 5tt 17 *1 -147 H-PTKUIV1AR USDA GRADATION TIST RESULTS Fig. 5 H.P*KUMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-',47 NATUFAL uotsTunE comENt &t NATURAL DRY DENSITY lpc0 GRAN PEFCENT PAS3l1{G NO.20o SIEVE SOILIYPE PtT DEPIH {nl GRAVEL ftl SAND t%l GFAVEL And COBBLES (ri) SAI{D (%l SILT (%t CLAY (%) 2 2 lo.4 77 29 Calcareous Silty Clayey Send (mrtrix) 3 to3th 55 2l 24 Silty Sandy Gravel with Cobbles Profile Pir I 3to4 4 67 r8 l3 7 Gravelly l-oamy Sard with Cobbles H.P\KUMAR TABLE 2 PERCOLATION TEST RE$ULTs PROJECT NA.17-7-147 HOLE NO. HOLE DEPTH (rNcHES) LENGTH OF INTERVAL (MrNl WATER DEPTHAT START OF INTERVAL (rNcHES) WATER OEPTH AT END OF INTERVAL (rNcHEs) OROP IN WATER LEVEL (rNcHES) AVERAGE PERCOLATION RATE (MlN.flNCHl P1 67 t5 WaterAdded WaterAdded 6U.8%% 15t1 714 6r/t 1Y. I 6r/t 11/t 6t/t $r/t I 8A 4'A I 4t/t gt/.I P2 s2 15 WaterAdded 9Ya 5 % 30rl 5 AtA 1t- 4Y.4 % 5t/.5 ,/t 5 4rA % 4rA 4 ,/t P3 4A 15 WaterAdded WatcrAdded WaterAdded I 5 ,l 30/1 7 6Y2 1v, 7Yt 8%2 tyz $r/t % 8t/t 6Y.Y2 5%4%Y2 Note: Percolatlon test holes wsre hand dug ln the bottom of backhoe plts and soaked on January 31,2017. Percolation tests were aonducted on February 1,2A17. The average percotatlon rates wer€ based on the lasttwo readings of each test.