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HomeMy WebLinkAboutSubsoil Study5020 County Road 154 Glenwood Springs, CO 81601 Phone: (920) 945-798S Fax (970) 94S-84S4 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit Counly, Colorado November 13,2018 Uriel Mellin 144 Cliffrose V/ay Glenwood Springs, Colorado 81601 uriel.mellin @hotmail.iom Subject: Project No.18-7-635 subsoil study for Foundation Design and Percolation Testing, proposed Residence, Lot23, callicotte Ranch, callicotte Ranch Drive, Garfield county, Colorado Dear Uriel: As requested, H-P/Kumar performed a subsoil study and percolation testing for foundation and septic disposal designs at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to you dated October 17,201.8. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construcfion: The proposed residence will be a one story wood fame structure over a partial basemenlpartial crawlspace located in the area of Pits 1 and 2 as shown on Figure l. Ground floors are proposed to be structural over crawlspace or slab-on-grade. Cut depths are expected to range between about 4 to 8 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 system is proposed to be located to the north ofthe residence. Ifbuilding conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: The site was vacant at the time of our site visit. The lot slopes gently to moderately down to the north. There is a dry drainage swale along the northern property line. The lot is vegetated with grass, weeds and sagebrush. Subsidence Potential: Callicotte Ranch is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum under H.PVKUMAR Geotechnlcal Enginearing I Engineerlng Geology Materiels Testing I Environmental - a çeffain conditions cân cause sinkholes to develop and can produce areas oflocalizecl subsidence. During previous work in the area, a sinkholc was observed about t/q ol amile to the no¡th- northeast of Lot 23, outside the Callicotte Ranch development. Sinkholes were not observed in the immediate area of the subject lot. Based on our present knowledge of the site, it cannot be said for certain that sinkholes will not develop. Tn our opinion, the risk of ground subsidence at Lot 23 is .low throughout fhe service life of the residence and similar to other lots in the area but the owner should be awa¡e of the potential for sinkhole development. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits in the general building area and two profile pits in the designated septic clisposal area at the approximate locations shown on Figure 1. The logs of the pits are presented on Figurc 2. The subsoils ettr.;uurttererl, below about I to Lr/zfeet of topsoil, consist of 7 feet of stiff, silty sandy clay to clayey sandy silt in Pit I and 2 feet of basalt gravel and cobhles in a sandy silt matrix in Pit 2' Reftisal to backhoe digging was encounte¡ed at 3 feet in pit 2. Results of swell- consolidation testing performecl on a relatively undisturbed sample of the sandy silty clay, 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 highly compressible under increased loading after wetting. The laboratory test results are summarized in Table 1. No free water was observed in the pits at the time of excavation and the soils were slightly moist. Foundation Recommendations: Considering the subsoil conditions cncountered in the exploratory pits and the nature of the proposed construction, spread footings placed on the undisturbed natural soil designed for an allowable soil pressure of 1 ,500 psfcan be used for support of the proposed ¡esidence. The soils tend to compress after wetting and there could be post-construction foundation settlement. Due to the variable subsurface conditions, settlements are expected to be differential especially if the bearing soils are wetted. Footings should be a minimum width of l8 inches for continuous walls and? feetfor columns. l,oose and disturbed soils and existing fill encountered at the foundation bearing level within the excavation snouls De removed and tne toCItlng bearing level extendecl down to the undisturbed natural soils. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Contittuous foundation walls should be ¡einforced top and bottom to span lrr:al atto¡rtalics such as by assuming an unsupported length of at least 12 feet. Foundation walls H.PtKUMAR Project No. 18-7-635 -3- acting as retaining structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for rhe on-site soii as backfill. Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade construction with a differential settlement risk. 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 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 507o passing the No. 4 sieve and less than2%o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at leasr. gíVo of maximum standard Proctor density at a moisture content near optimum. Required filI can consist of the on- site soils devoid ofvegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in mountainous areas 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 excavation and at least I foot below lowest adjacent finish grade and sloped at a minimuml7o ta a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain iess than 2Vo passingthe 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 LVzfeetdeep. 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. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: H-PVKUMAR Project No, 18-7-635 2) 1) 3) 4) -4- Inundation of the foundation excavations and underslab areas should be avoided during construction. Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum standard Proctor density in pavement and slab areas and to at Ieast 9O7o of the maximum standarcl Procfor clensity in landscape areas. Free-draining wall backfîll should be capped with about 2feet of the on-site, finer graded soils to reduce surface water infiltration. The ground surface sunounding 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 fust r0 feet in unpaved areas Rncl a minimum slope of 3 inches in the fîrst 10 feet in pavement and walkway areas Roof downspouts and drains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy inigation should be located ar least 10 feet from the building. Consider¿tion should be given to the use of xeriscape to limit potential wetting of soils berow the building caused by inigation. 5) Percolation Testing: Percolation tests were conducted on October 23,Z0Ig to evaluate the feasibility of an infiltration septic disposal system at the site. Two profile pits and three percolation holes were dug at the locations shown on Figure L The test holes (nominal 12 inch tliatrteter by 12 inch deep) were hand dug at the bottom of shallow backhoe pits and were soaked with watcr prior to testing. The soils exposed in the percolation holes are similar to those exposed in the Profile Pits shown on Figure 2 and consist of sandy clay loam. Results of a gradation analysis performed on a sample of the sancly clay loam (minus s/¿-inchfraction) obtained from Profile Pit I are presented on Figure 4. The percolation test results are presented in Table 2' Based on the subsurface conditions encountered and the percolation test results, the tested area should be suitable for a conventional infiltration septic disposal system. A civil engineer should design the infiltration septic clisposal system. tiuút¿tiu¡rs: This study has been conducted in accordance with generaliy accepted geotechnical engineering principles and practices in this area atthis time. We make no warranty either expressed or implied. The conclusions and recommendations submitted in this report are based upon the data obtained frolli the exploratory pits excavated at the locations indicated on Figure l, the proposed type uf constmction and our experience in the area. Our services do not include deterrnining the presence, prevention or possibility of mold or other biological contaminants H-P*KUMAR Project No. 18-7-635 5 (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 pits and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction'appear different from those described in this report, we should be notified at once so 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 recommenclations, 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 strucfural fill by a representative of the geotechnical engineer. ff you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, I{-P* KU Daniel E. Hardin, P.E Reviewed by: %T.QJL Steven L. Pawlak, P.E DE[Vkac attachments Figure 1 - Location of Exploratory Pits Figure 2.- Logs of Exploratory Pits Figure 3 - Swell-Consolidation Test Results Figure 4 - USDA Gradation Test Results Table 1 - Summary of Laboratory Test Results Table 2 - Percolation Test Results cc:Patrick Stukey stuarch @) comcast.net H.PVKUMAR Project No. 18-7-635 r9 I ! I E \\ I¡ \\ I \P\t LOT 25 P-lta AA i'.p-2 FnqflLE PtT 'ta \.' ,/ I \PROFILE PIT 2 ) \ ¡ PITPIT 2 1 /'^,,' oa,/ / *G1," '(":7' \I \ \\ I \ \ \/" LEGEND I EACKHOE PIT A PERCOLATION PITAPPROXIMATE SCALE-FEET r 8-7-63s H-PryKJMAR LOCATION OF IXPLORATORY PITS Fig. 1 r I I Ê PIT 1 EL.100'Ptl 2 EL. 95' PROFILE PIT 1 EL. I I'PROFILE PIT 2tL. 94' 0 Ful UJ Irt-o- t¡Jô q WC=8.6 DD=86 WC= 10.4 DÐ=80 -200=6 1 WC= 1 4.4 DD=64 -200=6 1 GRAVTL:8 SAND=30 SILT=30 CLAY=32 U q 10 ¡-LJ LiJ L I :Ê,-fL Lltô 'lo LEGEND ToPSolL; oRcANlC SANDy StLTy CLAY, FtRM, MOtsT. DARK BRowN. 991_ (9t)l ,sllrY, sANDy ro cLAyEy sANDy stLT, SCATTERED GRAVEL, sÏFF, sLtGHTLyMO'ST, LIGHT BROWN, CALCAREOUS. BASALT cRAvEL AND COBBLES (cp-GM); ¡N sANDy srLT MATRrx, DENsE, slrcHrly Morsï,WHITE. CALCAREOUS. HAND DRIVEN LINER SAMPLE. DISTURBED BULK SAMPLE I PRACTICAL DIGGING REFUSAL. NOTES F I ¿. 3. 4. ç 6. 7. THE EXPLORATORY PIÌS WERE EXCAVATED WITH A BACKHOE ON OCTOBER 22, 2018, ÏHE LOCATICINS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROMFEATURES SHOWN ON THE SITE PLAN PROVIDED. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TOPIT 1 GROUNÐ SURFACE AS ELEVATION IOO.O FEET. THE EXPLORATORY PIT LOCATIONS ANÐ ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLYTO THE DEGREE IMPLIED BY THE METHOD USED. THE LINES BETWEEN MATERIALS SHOWN ON lHE EXPLORATORY PIT LOGS REPRESENT îHEAPPR0XIMATE BOUNDARIES BETWEEN MATERIAL TYPÈs AND lle rñ¡NslloNs MAy BE cRADUAL. GROUNDWATER WAS NOT ENCOUNTEREO IN THE PITS AT THE TIME OF DIGGING. PITS WEREBACKFILLED SUBSEQUENT TO SAMPLING. LABORATORY TÊST RÊSULTSI wc = WATER CONTENT (%) (ASTM D 2216\; DD = DRY DENSTTY (pcr) (lsru D 2216); -2Qo = PERCENTAGE PASSTNG NO. 200 STEVE (ASTM D 1t4o);GRAVEL = PERCENT RETATNED ON NO. 10 STEVE; SAND = PERCENT PASSING NO. 10 SIEVË AND TiEÌAIN¡O ON N0.325 SIEVE;SILÏ = PERCENT PASSING NO. 325 SIEVE TO PARTICLE SIZ¡ .óbZVU;CLAY = PERCENT SMALLER THAN PARTICLE S'ZE .002MM. 1 8-7-635 H-PVKUMAR LOGS OF TXPLORATORY PITS lis. 2 3 E SAMPLE OF: Sondy Si$y Ctoy FROM:Pit1@3' WC = 86 %, D0 -- 86 pcf ADDITIONÀL COMPRESSION UNDER CONSTANT PRESSURT DUÊ TO WTTTiNC ) --z \ \ I ìq JJ 3 U1 I () Ë lf:() Øz. 0 _a _? *7 D PRE5SURE - KST IO r00 1 8-7-635 H.PVKUMAR SWELL_CONSOLIDATION TTST RTSULTS Fig. 3 t d -9 !:I I tj à 6 SIEVE U.S, 24H8. 7HR ' MIN- ^45 MIN,MIN,4 MIN,#140 460 *35 #18 *4 318"1 112" 3'.8"100 '10 90 20 s0 30 70 OLJ7a t!u F- soz L¡.j() &. t¡J o- w {I 60 zal/) 0_ Fz IlJ u llj o- 70 30 10 100 .001 .002 .005 .009 .01e .045 .106 .025 .500 1.00 2.00 47s 9.5 190 37.5 76.2 152 203 0 DIAMËTER OF PARTICLËS IN MILLIMETËRS CLAY co88r¡s GHAVTL 8 %SAND 30 %SILT 30 %CLAY 32 % FROM: Profile Pit 1 €) 2,-3, SILT USDA SO¡L TYPE: Sandy Ctay Loam 1 8-7*635 H-PryKUMAR USDA GRADATION TTST RTSULTS Fig. 4 H-P*KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.18-7-635Sandy Silty ClaySandy Silty ClaySandy Silty ClayClay Loam32SILT(%)30SAND(rol30GRAVEL(w8PERCENTPASSINGNO.200SIEVE6861SAND(vùGRAVEL0çtNÀTURALDRYDENSITY(pc0868064NATUIRALMOls']TUREcoNl'EN1(v,ù8.1610,4t4.4T'EPTH(ft)3J72to3PtlIProfilePir I H-P*KUMAR TABLE 2 PERCOLATION TEST RESULTS PROJECT NO. l8-7-635 HOLE NO.HOLE DEPTH (rNcHES) LENGTH OF INTERVAL (MrN) WATER DEPTH AT START OF INTERVAL (rNcHES) WATER DEPTH AT END OF INTERVAL (rNcHES) DROP IN WATER LEVEL (rNcHES) AVERAGE PERCOLATION RATE (MrN./tNCH) P-1 24 15 Water added 7%7 4/o 26 7 6%E/o 61A 5s/"Y" 5%5Y4 Y2 I 8%% 81/+7e/¿Yz P-2 32 15 Water added 7%6%1 23 6%57s t/o 5?/8 5Y4 % 5%4%% 8%7%% 7%7%3t P-3 36 l5 Water added 6%5%1% 16 5%4 1% 4 3 1 3 21A % 7%6 1% 6 5%7/" Note: Percolation test holes were hand dug in the bottom of backhoe p¡ts. percolation tests were conducted on October 23,2018. The average percoiation rates were based on the last three readings of each test.