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Home My WebLink AboutSubsoil Study for Foundation Design 09.23.08IIe¡rn'oltlr-Pau lak (ìe,¡,ttchnicaI, Irtc 1010 C-ì,rrnLy lìeracl I51 Lìlenti'r'o¡l Sl.r'illgs, Col,'r¡tlrr Nl (r(1 I Phone: 970-945-79iìE HEPWORTH - PAWLAK GEOTECHNICAL Fax,9/0-945-8-154 er-nail, hpgeo@hpge,,tecl-r.cc'n.t September 23,2008 Character Builders Attn: Steve Maznio P.O. Box 680 New Castle, Colorado 81647 Job No.108 5054 Subject:Subsoil Study for Foundation Design and Percolation Test, Proposed Residence and Future Shop, Parcel3, Simmons Subdivision Exemption, Canyon Creek, Garfield County, Colorado Dear Mr. Maznio: As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study and percolation test for foundation and septic disposal designs at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to Character Builders dated September 2,2008. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Evaluation of potential geologic hazard impacts on the site are beyond the scope of this study. Proposed Construction: The proposed residence will be a two story timber frame structure constructed with SIP panels above a walkout basement and will have a footprint of 45' by 36' . The future shop will be a two story structure. The residence and shop locations are shown on Figure 1. Ground floors are proposed to be slab-on-grade. Cut depths are expected to range between about 3 to 10 feet for the residence. 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 below the residence site. H Parli.-r l0l-B4l-71 l9 o (-'olor;r.lo Spr ings 7 19'611-5562 o 5ìilvcrthornc t)J¡l'{(i8- I 9ii!) a If building 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 property is located approximately 1.8 miles north of Highway 6 on the west side of Canyon Creek Road. Two abandoned county roads across the property are shown on Figure 1. Vegetation consists of sc rttered pinion and juniper trees, scrub oak, brush, grass and weeds. The residence and shop buildings are located at the base of a steep hillside and the building areas are relatively flat. The V/illiams Canal crosses the lower part of the property. Bear Wallow Creek bisects the property from the northwest to the southeast. A domestic well is proposed near the northeast corner of property. The future shop has been partially excavated. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits in the.building area, one exploratory pit in the future shop area and one profile pit in the septic disposal area at the approximate locations shown on Figure 1. The logs ofthe pits are presented on Figure 2. The subsoils encountered, below about one foot oftopsoil, consist of clayey to silty sandy gravel with cobbles and boulders. Three feet of gravelly sand clay was encountered in the Profile pit overlying the gravel. Results of a gradation analysis performed on samples of slightly silty sandy gravel with cobbles (minus 5 inch fraction) obtained from the site are presented on Figure 3. The laboratory test results are sufirmarized n Table L No free water was observed in the pits at the time of excavation and the soils were slightly moist to moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recornmend spread footings placed on the undisturbed natural soil designed for an allowable soil bearing pressure of 2,000 psf for support of the proposed residence and future shop. The soils tend to compress after wetting and there could be some post-construction foundation settlement if wetting were to occur. Footings should be a minimum width of 16 for continuous walls and 2 feel. for columns. Loose and disturbed soils and existing fill Job No.108 5054 cåFtecrr -J- encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended 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. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 10 feet. Foundation walls acting as retaining structrrres sha"l,{ be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 45 pcf for the on-site soil as backfill. Floor Slabs: The natural on-site soils, exclusive oftopsoil, 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 free-draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 nch aggtegate with less than 50o/o passing the No. 4 sieve and less than2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95%o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist ofthe 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 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 retanng walls and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. Job No.108 5054 c&Ftecrr 4 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 1 foot below lowest adjacent finish grade and sloped at a minimum ITo to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2o/o passngthe 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 I% feet deep. Surface l)rainage: The following drainage precautions should be observed during construction and maintained at all times after the residence and future shop have 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 95o/o of the maximum standard Proctor density in pavement and slab areas and to at least 90o/o of the maximum standard Proctor density in landscape areas. Free-draining wall backfill should be capped with about 2 feet" ofthe on-site, finer graded soils to reduce surface water infiltration. 3) The ground surface surrounding the exterior of the buildings should be sloped to drain away from the foundation in all directions. 'we recornmend 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 pavement and walkway areas. A swale may be needed uphill to direct surface runoff around the buildings. 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 5 feet from the building. Consideration should be given to the use of Job No.108 5054 cåBtecr' -5- xeriscape to limit potential wetting of soils below the building caused by irrigation. Percolation Testing: Percolation tests were conducted on September 3, 2008 to evaluate the feasibility of an infiltration septic disposal system at the site. One profile pit and three percolation holes were dug at the locations shown on Figure 1. The test holes (nominal 12 nchdiameter by 12 inch deep) were hand dug at the bottom of shallow backhoe pits and soaked with water one day prior to testing. The soils exposed in the percolation holes are similar to those exposed in the Profile Pit shown on Figure 2 and consist of one foot oftopsoil overlying sandy clay to 4 feet and silty sandy gravel with cobbles and boulders to the bottom pit depth of 7 feet. Results of a USDA gradation analysis performed on a sample of sandy loam (minus 5 inch fraction) obtained from the site are presented on Figure 4, Practical digging refusal was encountered in the gravel deposit. The percolation test rates varied from 20 minutes per inch to 40 minutes per inch. Test holes P2 and P3 were dug just below the upper clay soils and some infiltration of the clay soils may responsible for the slower percolation rates. 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. Limitations: This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. Vy'e make no warranty either expressed or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory pits excavated at the locations indicated on Figure 1, 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 ofpractice should be consulted. Our findings include interpolation and extrapolation ofthe 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 Job No. I 08 5054 cåEtec¡ -6- construction appear different from those described in this report, we should be notified at once so re-evaluation of the recoÍtmendations 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 recommendations, and to verifu 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 structural fill by a representative of the geotechnical engineer. If you have any questions or if we may be of fuither assistance, please let us know Respectfully Submitted, HEPWO PATVLAK GEOTE INC. E. Eller Reviewed by: Daniel E. Hardin, P.E. LEElvam attachments Figure I - Location of Exploratory Pits and Percolation Test Holes Figure 2 -Logs of Exploratory Pits Figure 3 - Gradation Test Results Figure 4 - USDA Gradation Test Results Table 1 - Summary of Laboratory Testing Table 2 - Percnlation Test Results Job No.108 5054 cåEtecr, PARCEL 3 SIMMONS EXEMPTION ,"'l I I PROPERry BOUNDARY //// APPROXTMATE ,/,/ HOUSL / t LocAIoN ì5(*1 pr I// \ ././ a Ptr 2/ / P1// a// A I PROFILE,/ P2 aPlT P3 *vLut C) Èo -J-Js Þ ABANDONED FUTURE GARAGE/SHOP AREA I PIT 3 q ,Í a3COUNTY ROADS /---- /tt - o PROPOSED WELL\ 2ul UJ U) ul \ APPROXIMATE SCALE 1" : '150' 'J4-z4o \ 1 08 5054 LOCATION OF EXPLORATORY PITS AND PERCOLATION TEST HOLES Figure 1 PIT 1 PIT 2 PIT 3 PROFILE PIT 0 ry 0 WC:5.9 t +4:54 - r -200:12 WC=3.3 - - +4:40 t,-2oo:29 q''LL:zz Pl:4 d)q) LL I -c o_ o)o 5 _ _ wc:3.6 r +4:56 - r -200:10 q) 0) LL I -c o_oo 10 10 LEGEND: TOPSOIL; organic sandy silt and clay, scattered gravel, firm, slightly moist, dark brown. CLAY (CL); sandy, silty, scattered gravel and cobbles, stiff, slightly moist, brown ffi 1,..t:.QI ffi t: T GRAVEL (GM); silty, clayey, sandy, with cobbles and boulders, dense, slightly moist, brown, subrounded rock. GRAVEL (GP-GM); silty, sandy, with cobbles and boulders, dense, slightly moist, brown, subrounded rock. Disturbed bulk sample Practical digging refusal. NOTES: 1. Exploratory pits were excavated on September 3, 2008 with a Yanmar VIO 45 mini excavator. 2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory pits were not measured and the logs of exploratory pits are drawn to depth. 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 materialtypes and transitions may be gradual. 6. No free water was encountered in the pits at the time of excavating. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: WC : Water Content (%) *4 : Percent retained on the No. 4 sieve -200 : Percent passing No. 200 sieve LL: Liquid Limit (%) Pl : Plasticity lndex (%) 108 5054 LOGS OF EXPLORATORY PITS Figure 2 SIEVE ANAL TIME BEADINGS U,S. STANDARD SERIES CLEAR SQUARE OPENINGS ?'df;¡1ru. rËT¡n.60MrNieMrN.4 MrN. 1 MrN. #2oo #1oo #50 #30 #16 #B #4 3/8' s/4' 1 112' 3' 5'6' 8" o LUz F- t-uEt-z LU()E LU a_ 0 10 20 30 40 50 60 70 BO 90 100 100 90 80 70 60 50 40 30 20 10 0 oz U) U) o_t-z u-l() E- LU o_ .001 .002 .005 .oo9 .019 .037 .074 .150 .300 ,600 1.18 2.36 4.75 9.U ,r.u 19.0 37.5 76.2 152 203 127 DIAMETER OF PARTICLES IN MILLIMETERS TIME READINGS7HB 15 MlN.60MtN1gMtN.4 MtN. 1 MtN. #200 #100 U.S. STANDARD SERIES #50 #30 #16 #8 COBBLES CLEAR SQUARE OPENINGS 3/8. s/4, 1 112" 3" 5'6' CLAYTO SILÍ GRAVEL 56 "/o SAND 34 "/" SILTANDCLAY 10 % LIQUID LIMIT % PLASTICITY INDEX % SAMPLE OF: Slightly Silty Sandy Gravelwith Cobbles FROM: Pit 2 at 4 to 5 Feet 24 45 0 #4 ar 80 CI ,OZ CN U) OUL F-"" z. () ooffi o_ oulz F LU E. t--zlrlOÉ LU o_ 10 20 30 40 50 60 70 80 90 100 100 90 20 10 0 30 .001 .002 .005.009 ,019 .OS7 .074 .tSO .300 .600 1.18 2.36 4.75 DIAMETER OF PARTICLES IN MILLIMETERS 9.512 519.0 37.5 76.2 pr52 203 --+--- * ----r---IlI----------- I- III- l- I- IIt-¡- ------1 -E---t III-III -I---II IIII-I -r-----------r-E--rr-¡----- FINE COAFSE = 1 ---I---n ---- ---- n - I - ---I---- I- -I---- ------ ----- --II --IT --------n--- ---E CLAY TO SILT I eÁNñ I êÞ^vFr I I FINE I MEDIUM I COARSE I FINE I COARSE I COBBLES GRAVEL 54 % SAND 34 % SILTANDCLAY 12 % LIQUID LIMIT % PLASTICITY INDEX O/O SAMPLE OF: Sliohtlv Siltv Sandv Gravelwith Cobbles FROM: Pit 3 at2fo 3 Feet 108 51 1A & Heoworth-Powlok Geotechnlcol GRADATION TEST RESULTS Figure 3 TIME READINGS U.S. STANDARD SERIES #50 #30 #16 #B CLEAR SQUARE OPENINGS 24 HR. 7 HR 0 45 MlN. 15 MIN 60MlN1gMlN.4 MtN. '1 MtN. #200 #100 #4 3/B' 3/4', 1 112" 3" 5u6' 8',100 t0 90 20 80 30 70 ôlJ 40z. t-lrl É. t- 50zIJ(J É. UJÈ60 60 50 40 30 20 C'z6Ø À t-z. l¿J C) É. bJÀ 70 80 90 10 100 0 .001 .002 .005.009 .019 Og7 .OT4 .1 50 .OOO .600 1 . 18 2.36 4.75 9.5 12.5 DIAMETEB OF PARTICLES IN MILLIMETERS 19.0 37.5 76.2 152 203 127 CtAY COBBLES Cobbles 10 % GRAVEL 34 %SAND 27 %SILT and CLAY 29 o/o LIQUID LII'/IT 22 "/O PLASÏICITY INDEX 4 % FROM:Profile Pit at 4 to 5 Feet SILT USDA SOIL TYPE: Sandy Loam 1 08 5054 USDA GRADATION TEST RESULTS Figure 4 H EPWORTH-PAWLAK GEOTECH NICAL, INC.TABLE 1SUMMARY OF LABORATORY TEST RESULTSJob No. 108 5054SOIL ORBEDROCK TYPESlightly Silty Sandy Gravelwith CobblesSlightly Silty Sandy Gravelwith CobblesSandy LoamUNCONFINEDCOMPRESSIVESTRENGTHATTERBERG UMITSPLASTCINDEX(o/o\4LIQUIDLIMIT(o/o)22NATURALDRYDENSITYGRAVEL(%)SAND(vo)PERCENTPASSINGNO. 200SIEVE341012293431565440SAMPLE LOCANATURALMOISTURECONTENTPITDEPTH3.6s.9J.J4to52to34to52JProfilePit H EPWORTH-PAWLAK GEOTECH NICAL, INC. TABLE 2 PERCOLATION TEST RESULTS JOB NO. 108 5054 Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked on September 2,2008. Percolation tests were conducted on September 3, 2008. The average percolation rates were based on the last two readings of each test. HOLE NO.HOLE DEPTH (rNcHES) LENGTH OF INTERVAL (MrN) WATER DEPTH AT SÏARÏ OF INTERVAL (INCHES) WATER DEPTH AT END OF INTERVAL (INCHES) DROP IN WATER LEVEL (rNcHES) AVERAGE PERCOLAÏON RATE (MrN./rNCH) P1 60 10 Water added 4 Ll4 3 rl2 314 20lr 3 rl2 3 r/2 3 2 L/2 Ll2 2 r/2 2 Ll2 2 L 314 Ll4 5 4 L/4 3/4 4I/4 3 3/4 L/2 3 3/4 3 Ll4 3 Ll4 2 314 Ll2 Ll2 P2 42 10 7 6 L/4 3/4 40lr 6 r/4 s Llz 3/4 s rl2 5 rl2 5 4 rl2 tl2 4 L/2 4 r/2 4 3 rl2 3 r/2 3 L/2 Llz 3 2 314 Ll4 2 314 2 Llz rl4 P3 36 10 7 6 L/4 314 40lr 6 rl4 s rl2 314 s Llz 5 r12 5 4 3/4 L/4 4 314 4 rl4 tl2 4 Ll4 3 314 rl2 3 314 3 Ll4 r12 3U4 3 rl4 3 2 314 r/4 T* a, 5