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Home My WebLink AboutSubsoils Report for Foundation DesignH-PVKUMAR 9eotechnlcal Engineering I Engineerlng GEology Materlals Testlng I Environmental 5020 County Road 15¿Í Glenwood Springs, CO gf 60f Phone: (920) 945-7989 Fax (970) 945-8454 Email: hpkglenwood@kumârusa.com Office Locations: Denver (HQ), Parke¡ Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado December ll,2Ol7 ay 630 East Hyman Avenue, Suite 101 Aspen, Colorado 81611 j ay.wl'i ght @ qllipan,cpm Project No.17-7-787 Subject:subsoil study for Foundation Design and Percolation Testing, proposed Residence, Lot23, stirling Ranch, skipper Drive and schooner Lane, Missouri Heights, Garfield County, Colorado 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 20,2017. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: This report was for the purchase/sale of the property in which the Clary's are the buyers. Design plans for the residence have not been developed. rüy'e assume that the proposed residence will be a one to two story wood frame structure over a basement or crawlspace and located on the site in the area of Pits I and2, shown on Figure L Ground floors will be slab-on-grade or structural over crawlspace. Cut depths are expected to range between about 2 ta7 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 south of the residence in the area of the profile pits and percolation test holes shown on Figure 1. 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 lot was vacant and the topography appeared to be natural at the time of our field work. An existing fence line runs north to south through the eastern portion of the lot. There are pinon and juniper trees to the west of the fence and sage brush to the east. There is an -2- understory of grass and weeds across the lot. The lot slopes gently to moderately down to the southwest. Scattered basalt cobbles and boulders were observed on the ground surface. Subsidence PotentÍal: The lot is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas oflocalized subsidence. During previous work in the area, sinkholes were observed in the lower Roaring Fork Valley. Sinkholes were not observed in the immediate area of the subject lot. The pits were relatively shallow, for foundation design only. Based on our present knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot23 throughout the service life of the residence is low and similar to other lots in the area but the owner should be aware of the potential for sinkhole development. 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 septic disposal area at the approximate locations shown on Figure l The logs of the pits are presented on Figure Z. The subsoils encountered, below about I to lVz feet of topsoil, consist mainly of dense, basalt cobbles and boulders in a sandy clayey silt matrix. About lr/zfeetof sandy silty clay with basalt rocks was encountered between the topsoil and mostly basalt rocks in Profile Pit 2 in the southe¡n part of the septic area. Results of swell-consolidation testing performed on relatively undisturbed samples of sandy clayey silt matrix soils, presented on Figures 3 and 4,indicate low compressibility under existing moisture conditions and light loading and no to low collapse potential when wetted. The samples were moderately compressible under increased loading after wetting. Results of a gradation analysis performed on a sample of gravelly sandy loam (minus 3 inch fraction) obtained from the site are presented on Figure 5. 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: Development of a residence on the lot should be feasible from a geotechnical point of view. Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recorlmend spread footings placed on the undisturbed natural basalt rock soil designed for an allowable soil bearing pressure of 2,000 psf for support of the proposed residence. The matrix soils tend to compress after wetting and there could be some post-construction foundation settlement. Footings should be a minimum width of 16 inches for continuous walls and2 feet for columns. Loose and disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing H.P!KUMAR Proienl Nô 17-7-7R7 -3- 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 structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcffor the on-site soil as backfill excluding topsoil and rock larger than about 6 inches. Excavation below about 5 feet at this site will be difficult. Our experience in the Missouri Heights area is that a typical good-sized trackhoe excavator used for residential construction should be capable of excavating about 2feet deeper in a foundation excavation than the depth where refusal to digging was encountered in our pits. Nanow excavations such as utility trenches and tight excavation corners may only be able to be excavated to the depth of our pits. Deeper excavations will likely require rock excavation techniques such as chipping or blasting. Floor 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 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 than 27o passingthe 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, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the area that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also 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 sumounded above the invert level with free-draining granular material. The drain should be placed at each level of H.PèKT,,MAR Project No.17-7-787 -4- excavation and at least I foot below lowest adjacent finish grade and sloped at a minimu m l7o to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less 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 172 feet deep. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: l) 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 957a 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. Free-draining wall backfill should be capped with about 2 feetof the on-site, finer graded soils to reduce surface water infiltration. 3) The ground surface surounding the exterior of the buitding 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 pavement and walkway areas, A swale may be needed uphill to direct surface runoff around the residence. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. Percolation Testing: Percolation tests were conducted on November 13, Z0l7,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 1. The test holes (nominal 12 inch diameter by 12 inch deep) were hand dug at the bottom of shallow backhoe pits and were soaked with water 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 gravelly sandy loam to sandy loam. 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. We recommend the infiltration area be oversized due to the variable percolation rate. 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 wananty either expressed or implied. The conclusions and recommendations submitted in this report are based H.P€KUIVIAR Project No. 17-7-787 -5- upon the data obtained from the exploratory pits excavated at the locations indicated on Figure l, 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 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 recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recomrnendations 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 further assistance, please let us know. Respectfully Submitted, H.P+KUMAR Daniel E. Hardin, P Reviewed by: **,/- Steven L. Pawlak, P.E DEH/kac attachments Figure I - Location of Exploratory Pits Figure 2 * Logs of Exploratory Pits Figures 3 and 4 - Swell-Consolidation Test Results Figure 5 - USDA Gradation Test Results Table I - Summary of Laboratory Test Results Table 2 -Percolation Test Results H.PæKUfVIAR Project No.17-7-787 t Yì ii lr LOCATION OF EXPLORATORY PITSH-PVKUITVIAR t- \{I I I ( I I I O ¡t5E-4¡$ tr ¡fh-rl¡n A -:.bc-r r trD 05t {ü LlttÈ alb +*,tÈ¡¡ -r_b APPROXIMATE SCALE-FEET r 60 0 60 120 I I *l¡e I I \I \ / E \ ¿ t'-*a- b II I\\I -tslU-/ P-3 I I I II I\ I 4---Ä\ P-2 A PROFILE PIT r-î t I I I ì I t I PITI tA I t ^l A \ I I I 4 2 / À I{tT23fiIr¡7E I PIT 2 \ \ 17 -7 -787 € I I I ^\-^.\- 'r/= PIT 1 PIT 2 PROFILE PIT I PROFILE PIT 2 t- L¡J tÀJl¡ IIl-Lt¡o t- ÙJ l¡J LL I :Et--(L l¡JÕ 0 5 WC='t 1.4 tD=77 -240=7O WC=13.1 DD=74 -2O0=79 -l WC=7.4 -t GRAVEL=ZO SAND=34 SILT=29 CLAY=17 WC=6.5 -200=76 LL=54 Pl=14 -t 0 5 ToPSolL; oRGANlc SANDY CLAY AND stLT, wtTH GRAVEL AND coBBLEs, F|RM, MotsT, DARKBROWN. BASALT COBBLES AND .BOULDERS (GM): IN SANDY CLAYEY SILT MATRIX, DENSE, SLIGHTLYMOIST, WHIÏISH BROWN. CLAY (CL): SANDY, SILTY, WITH BASALT GRAVEL, VERY STIFF, SLIGHTLY MOIST, BROWN. z_INCH DIAMÊTER HAND DRIVEN LINER SAMPLE. DISTURBED BULK SAMPLE. I PRACTICAL DIGGING REFUSAL. NOTES þ 2, 3. 4. 5. 6. 7. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON NOVEMBER 13,2017. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROMFEATURES SHOWN ON THE SITE PLAN PROVIDED. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THEEXPLORATORY PITS ARE PLOTTED TO DEPTH. THE EXPLORATORY PIT LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREEIMPLIED BY THE METHOD USED. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THEAPPRoXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIoNs MÃi-BE öneoual. GROUNDWATER WAS NOT ENCOUNTEREO IN THE PITS AT THE TIME OF ORILLING, PITS WEREBACKFILLED SUBSEQUENT TO SAMPLING. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM O 2216)I DD = DRY DENSITY (pcf) (ASTM A 2216)t -200 = PERCENTAGE PASSTNG N0. 200 StEvE (ASTM D il40);LL = LIQUID LIMIT (ASTM D 431S);Pl = PLASTICITY INDEX (ASTM D atl8); GRAVEL = PERCENT RETAINED ON N0. 10 SIEVE sAND = PERCENT PAsstNG No. t0 stEVE AND RETAINED oN No. g2s stEVESILT = PERCENT PASSING NO. 3ZS STEVE TO PART|CLE S|ZE .002mm CLAY = PERCENT SMALLER T|{AN PARTTCLE S|ZE .002mm oz 17 -7 -787 H-PryKUMAR LOGS OF EXPLORATORY PITS Fi1. 2 È I SÂMPLE OFr Sondy Cloyey Sill Matrix FROM:Pil 1@3' WC = 11.4 %, ÐÞ = 77 pef *2tÇ = 7t % NO MOVEMENT UPON WFTTING I \ I ¡êt bå r¿lrodûrën, lh6 rdlten oÞgrrvol ôltusr.;€i.!. ¡rô. ssÊl¡ bs JJItl3 v') I z Ë4 ¿f =ÐtnzÕ CJ o *2 *4 _'7 1,0 ÅPFLIIT P l0 r00 17 *7 *787 H-PryKUMAR SWTLL-CONSOLIDATION TEST RISULTS Fig. 3 È € Ií SAMPLE ûFr Sondy Clcyey Sift Molrix FROM:Pit2@3' WC = 13.1 %, DD = 74 pcf ^2AO = 79 % I ADDITIONAL CCIMPRESSION UNOER CCINSTANT PRESSURE DUE TÛ WETTING I ) lh6 0 JJ L¡J I IÕË Õ C) lr1 o -l *2 a_J 4 -*¡i -6 *7 t.0 ÂPPLIEO - KSF l0 10û 17 -7 -787 H.PryKUMAR SWELL-CONSOLIDATION TTST RESULTS Fig. 4 .¡ ı b E 24Hff, 7HR I MIN. #325045 #60 +35 #18 #4 sle 1 5'6', 8' "t /-.: 100 10 90 20 80 3û 70 c)t!Z F LiJv. F-z lJJ(J E LrJ o_ 40 60 (J z. U) U) Õ- F-ztdO E. L¡.j& 50 50 60 40 70 30 20 90 10 100 -001 .002 .005 00s .0rs 045 106 .025 .500 f.@ 2_00 4.7s 9.5 19.0 37.5 76.2 152 æ3 0 DIAMETËR OF PARTICLES IN MILLIMETERS ÔLAY coEBtËS GRAVEL 20 %SAND 34 O/"SILT 29 %CLAY 17 % USDA SOIL TYPE: Gravelly Sandy Loam FROM: P¡t1 @1,5,-2.S' sÂNOslltv FINE I F|NE I MËDruM I COAFTS€ lv. coÆsFl ! 17 -7 --"787 H-PryKUMAR USDA GRADATION TIST RISULTS t'ig. 5 H-P*KUMAR TABLE I SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-787 SOILTYPE Sandy Clayey Silt Matrix Sandy Clayey Silt Matrix Gravelly Sandy Loam Sandy Loam CLAV (r"l 1 7 (LL = 34) (PI = 14) SILT (%'t 29 SAND (v", 34 GRAVEL (1") 2A PERCENT PASSING NO.200 SIEVE 70 79 76 SAND l%l GRAVEL (%) NATURAL DFV DENSITY {pc0 77 74 NATURAL MOISTUFE CONTENT (v., tt.4 I 3.I 7.4 6.5 )CATION T}EPTH (ft) 3 3 IVz-ZVz lY2-2Y2 PIT t 2 Profile Pir 1 Profile Pit2 H:P*KUMAR TABLE 2 PERCOLATION TEST RESULTS PROJECT NO. l7-7-787 Note: Percolation test holes were hand dug in the bottom of backhoe pits. percotation tests were conducted on November 13,2017. 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 START OF INTERVAL (rNcHES) WATER DEPTH AT END OF INTERVAL (rNcHES) DROP IN WATER LEVEL (rNcHES) AVERAGE PERCOLATION RATE (MtN./tNCH) P-1 26 30 7 5Y"13/t 60 51 41/4 1 4v,3Y4 1 31/o 23/*% 2t/c 2%1/2 P-2 25 30 9s/t I 1% 40 I 71h 4/¿ 7Y1 6'ta 1 6Y4 5%% 5Y2 4a/q E/q P-3 28 30 81/A 7%Yz 34 7%6 1E/t 6 4t/¿11 43/a 4 % 4 3 1