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HomeMy WebLinkAboutSoils Report for Foundation Design and Perc Test 10.15.2018cl^ - r--, Geotechnical Engineering 1 Engineering Geology Materials Testing 1 Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwood©kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado October 15, 2018 Ralph Delaney 203 Haystack Road Glenwood Springs, Colorado 81601 (drdelaney53 @ gmail.com) Project No. 18-7-558 Subject: Subsoil Study for Foundation Design and Percolation Testing, Proposed Cabin, 131 Black Bear Road, West of Lot 17, Mountain Springs Ranch, Garfield County, Colorado Dear Ralph: 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 general accordance with our agreement for geotechnical engineering services to you dated August 31, 2018. 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 cabin will be a 11/ story log structure over a walkout basement located on the site as shown on Figure 1. The basement floor will be slab -on -grade. Cut depths are expected to range between about 2 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 downhill to the west of the cabin. 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. We also excavated a profile pit for a proposed shop building and performed percolation testing near an existing hunting cabin located on the property about 500 feet to the west and downhill of the proposed new cabin. 2 Site Conditions: The site of the proposed cabin is located on a southwest -facing slope which varies from about 10% grade in the building area to 40% grade below the building area. Vegetation consists of oak brush and scattered pine trees with an understory of grass and weeds. Basalt cobbles and boulders were observed on the ground surface. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits in the proposed cabin area and two profile pits in the septic disposal area at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about 1h to 11/2 feet of topsoil, consist of relatively dense, basalt cobbles and boulders in a sandy clay matrix down to the Pit 1 depth of 8 feet. Refusal to backhoe digging was encountered in Pit 2 at 6 feet. Approximately 60% of the basalt rock material was greater than 3 inches in size. Results of swell -consolidation testing performed on relatively undisturbed samples of the clay matrix soils, presented on Figure 4, indicate low compressibility under existing moisture conditions and light loading and a low to moderate expansion potential when wetted. The samples were moderately 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. The subsoil conditions encountered in Profile Pit 3, located about 35 feet southeast of the existing hunting cabin, consisted of about 1 foot of topsoil and 2 feet of stiff, silty sandy clay overlying 5 feet of medium dense silty sand with scattered cobbles. Results of swell - consolidation testing performed on a relatively undisturbed sample of the silty sand soils, presented on Figure 5, indicate low compressibility under existing moisture conditions and light loading and a minor collapse potential when wetted. The sample was moderately compressible under increased loading after wetting. No free water was observed in Profile Pit 3 at the time of excavation. Foundation Recommendations (Proposed Cabin): 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 soil designed for an allowable soil bearing pressure of 3,000 psf with a minimum dead load pressure of 800 psf for support of the proposed H-P%'KUMAR Project No. 18-7-558 -3 - cabin. The matrix soils tend to expand after wetting and there could be some post -construction foundation movement. Footings should be a minimum width of 16 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 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 42 inches below the exterior grade is typically used in this area which is at about 8,100 feet elevation. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 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 pcf for the on-site soil as backfill. Foundation Recommendations (Proposed Shop): The proposed shop near the existing hunting cabin can be supported on spread footing foundations placed on the silty sand soils designed for an allowable soil bearing pressure of 2,000 psf. Floor Slabs (Proposed Cabin): The on-site soils at the proposed cabin site possess an expansion potential and slab heave could occur if the subgrade soils were to become wet. Slab - on -grade construction may be used provided precautions are taken to limit potential movement and the risk of distress to the building is accepted by the owner. A positive way to reduce the risk of slab movement, which is commonly used in the area, is to construct structurally supported floors over crawlspace. To reduce the effects of some differential movement, nonstructural floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Interior non-bearing partitions resting on floor slabs should be provided with a slip joint at the bottom of the wall so that, if the slab moves, the movement cannot be transmitted to the upper structure. This detail is also important for wallboards, stairways and door frames. Slip joints which will allow at least 11/2 inches of vertical movement are recommended. Floor slab control joints should be used to reduce damage due to shrinkage cracking. Slab reinforcement and control joints should be established by the designer based on experience and the intended slab use. H-PKUMAR Project No. 18-7-558 4 - We recommend vapor retarders conform to at least the minimum requirements of ASTM E1745 Class C material. Certain floor types are more sensitive to water vapor transmission than others. For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum requirements of ASTM E1745 Class A material. The vapor retarder should be installed in accordance with the manufacturers' recommendations and ASTM E1643. Floor Slabs (Proposed Shop): The natural on-site soils at the proposed shop area, 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 slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% 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 areas 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. We assume that the proposed shop building will have a slab -at -grade floor and should not require an underdrain. 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 H-PkiKUMAR Project No. 18-7-558 -5 - excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular material used in the underdrain system should contain less than 2% passing the 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 11/2 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. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the proposed cabin has been completed: 1) Inundation of the foundation excavations and underslab areas should be avoided during construction. Drying could increase the expansion potential of the soils. 2) 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 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 infiltration. 3) The ground surface surrounding 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 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 cabin. 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 10 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. Percolation Testing: Profile Pits 1 and 2 were dug near the proposed cabin site as shown on Figure 1. The soils encountered in the pits, below about 1/2 foot of topsoil, consisted of extremely gravelly loamy sand, see gradation shown on Figure 6. H-PMKUMAR Project No. 18-7-558 -6 - Profile Pit 3 and two percolation holes were dug near the proposed shop location. Percolation tests were conducted on September 11, 2018 in the proposed shop area to evaluate the feasibility of an infiltration septic disposal system at the site. 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. The soils exposed in the percolation holes are similar to those exposed in Profile Pit 3 and consist of slightly clayey, silty sand, see gradation shown on Figure 7. The percolation test results are presented in Table 2. Based on the subsurface conditions encountered and the percolation test results, the tested areas should be suitable for a conventional infiltration septic disposal system. A civil engineer should design the infiltration septic disposal systems. 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 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 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 recommendations presented herein. We recommend on-site observation H-PtKUMAR Project No. 18-7-558 -7 - 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; KUMAI Daniel E. Hardin, P.E. Reviewed by: Steven L. Pawlak, P.E. DEH/kac attachments Figure 1 — Location of Exploratory Pits Figure 2 — Logs of Exploratory Pits Figure 3 — Legend and Notes Figures 4 and 5 - Swell -Consolidation Test Results Figures 6 and 7 — USDA Gradation Test Results Table 1 — Summary of Laboratory Test Results Table 2 — Percolation Test Results H-P%KUMAR Project No. 18-7-558 PROFILE PIT 1 ■ 10 0 10 20 APPROXIMATE SCALE—FEET PIT 1 0 ■ 0 - -,__ \PROFILE PIT 2 0 / ~ -- - PIT 2 �t / Pine 10' Radius Drip Line — Found Rebar NOTE: PROFILE PIT 3 AND PERCOLATION TESTS ARE LOCATED NEAR EXISTING CABINS ABOUT 500 FEET DOWNHILL AND WES1OF THIS PROPOSED CABIN. 18-7-558 H -P- KUNIAR LOCATION OF EXPLORATORY PITS Fig. 1 0 0 5 - 10 0 5 10 PROFILE PIT 1 EL. 8104' PIT EL. 8110' GRAVEL=78 _I SAND=5 SI LT=9 CLAY=8 WC=17.8 DD=95 PROFILE PIT 2 EL. 8105' PIT 2 EL. 8105' WC=16.6 DD=98 PROFILE PIT 3 WC=15.6 DD=91 0-- 5 10 GRAVEL=1 SAND=55 SILT=37 CLAY=7 1- w w 0_ w 0 0 5 10 18-7-558 H -P KUMAR LOGS OF EXPLORATORY PITS Fig. 2 LEGEND TOPSOIL, ORGANIC SANDY SILTY CLAY WITH BASALT COBBLES, FIRM, SLIGHTLY MOIST, DARK BROWN. BASALT COBBLES AND BOULDERS (GC): IN SANDY CLAY MATRIX, DENSE, SLIGHTLY MOIST, DARK BROWN. CLAY (CL): SILTY, SANDY WITH SCATTERED COBBLES, STIFF, MOIST, BROWN, SLIGHTLY / ORGANIC. PROFILE PIT 3 ONLY. SAND (SM): SILTY, WITH COBBLES, SLIGHTLY CLAYEY, MEDIUM DENSE, MOIST, BROWN. PROFILE PIT 3 ONLY. SI HAND DRIVEN 2—INCH DIAMETER LINER SAMPLE. DISTURBED BULK SAMPLE. 1 PRACTICAL DIGGING REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON SEPTEMBER 11, 2018. 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 THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF DIGGING. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); GRAVEL= PERCENT RETAINED ON No. 10 SIEVE SAND= PERCENT PASSING No. 10 SIEVE AND RETAINED ON NO. 325 SIEVE SILT= PERCENT PASSING No. 325 SIEVE TO PARTICLE SIZE .002mm CLAY= PERCENT SMALLER THAN PARTICLE SIZE .002mm 18-7-558 H -P KUMAR LEGEND AND NOTES I Fig. 3 CONSOLIDATION - SWELL CONSOLIDATION - SWELL 0 2 1 0 —2 —3 SAMPLE OF: Sandy Clay Matrix FROM: Pit 1 ® 5' WC = 17.8 %, DD = 95 pcf 1,0 APPLIED PRESSURE — i(SE EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 10 100 SAMPLE OF: Sandy Clay Matrix FROM: Pit 2 0 4' WC = 16.6 %, DD = 98 pcf thf.a l..l rein. tippy Iffy if the sonspl4s iniad the 14.j1 n9 rtport .,roll OI M nprOdeled, ...pi in NU, .010L.r the .r.Ii1n egpev j 01 Winer end Anacin, Inc S.e'r Cpn.N{delien p.riprrn.d In OCCOMMp. .11,s A$1Y R-4$46 1.0 APPLIED PRESSURE - KSF ID EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 100 18-7-558 H-PtiKUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 4 1 .. 0 — CONSOLIDATION - SWELL – 2 – 3 -4 – 5 Irmo toll vemWta apply , 1y p, th. remyes tested. The leaf:nq raper! Map .01 be r.producea, e.C.p! :. fuer, .01,evl IM ml ten approval of Kum., and Outeoc.olrt. Inc. 5aee Ce..elideren lied p n.e in ncaaAv le..11h 76111p, Q-.516 SAMPLE OF: Clayey Silty Sand FROM: Profile Pit 3 0 5' WC = 15.6 %, DD = 91 pcf 1.0 APPLIED PRESSURE - KSF ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 10 101 8-7-558 H-PWIJMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 5 PERCENT RETAINED 10 20 30 40 50 70 BO 100 24 YR 45 MAI. HYDROMETER ANALYSIS f TIME READINGS SIEVE ANALYSIS 7 R9 114N. 15 YAW. 006TH. 1514E IINkL 0325 U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS 140 #60 035 118 #10 .001 .002 .005 .009 .019 .045 .106 .025 .500 1.00 2.00 4 3/4' 11/2' 3' 5' 6' 4.75 9.5 19.0 37.5 76 2 152 203 DIAMETER OF PARTICLES IN MILLIMETERQ CLAY SILT SAND VANE 1 F11.4 1 MEOW 1 cOArISE• SMALL 1 MEDIUM GRAVEL 78 % SAND 5 % LARGE COBBLES SILT 9 % CLAY 8 % USDA SOIL TYPE: Extremely Gravelly Loamy Sand FROM: Profile Pit 1 @ 2-3' 100 90 80 70 50 40 30 20 10 0 PERCENT PASSING 18-7-558 H -P KUMAR USDA GRADATION TEST RESULTS Fig. 6 PERCENT RETAINED HYDROMETER ANALYSIS f TIME READINGS 241111. 71111 o45 AM ISAIN_ 10 20 30 40 50 60 70 80 90 100 SIEVE ANALYSES U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS 1 MRN. 60M8L 0049L 4M. 9325 9140 #60 #35 #18 910 #4 318' 3/4' 1 1.? 3' 5' 6' .001 .002 .005 .009 .019 .045 .106 .025 .500 1.00 2.00 4.75 9.5 19.0 37.5 76.2 DIAMETER OF PARTICLES IN MILLIMETERS SILT GRAVEL 1 % V. FINE satin MEM =Eli GRO11. SAND 55 % SILT 37 % USDA SOIL TYPE: Very Sandy Loam URGE 100 90 80 70 60 50 40 30 20 10 0 152 203 COBBLES CLAY 7 % FROM: Profile Pit 3 @ 4-4.5' PERCENT PASSING 8-7-558 H -P KllMAR USDA GRADATION TEST RESULTS Fig. 7 TABLE 1 SUMMARY OF LABORATORY TEST RESULTS SAMPLE LOCATION j NATURAL NATURAL GRADATION I PERCENT USDA SOIL TEXTURE MOISTURE DRY PASSING PIT DEPTH CONTENT DENSITY GRAVEL SAND NO. 200 GRAVEL SAND SILT CLAY SIEVE (ft) l (%) J (Pcf) (%) (%) I (%) (%) (%) (%) Project No.18-7-558 SOIL TYPE 1 5 17.8 95 Sandy Clay Matrix 2 4 16.6 98 Profile Pit 1 2-3 Profile 4-41/2 Pit 3 5 15.6 91 Sandy Clay Matrix 78 5 9 8 Extremely Gravelly Loamy Sand 1 55 37 7 Very Sandy Loam Clayey Silty Sand i HP1(UMAR TABLE 2 PERCOLATION TEST RESULTS PROJECT NO. 18-7-558 HOLE NO. P-1 P-2 HOLE DEPTH (INCHES) 28 33 LENGTH OF INTERVAL (MIN) 10 WATER DEPTH AT START OF INTERVAL (INCHES) 91/4 WATER DEPTH AT END OF INTERVAL (INCHES) 9 9 8% 8% DROP IN WATER LEVEL (INCHES) AVERAGE PERCOLATION RATE (MIN./INCH) 1/4 3/B 81/4 3 81/4 8 8 73/4 1/4 1/4 73/4 10 8 71/2 1/4 40 71/4 3/4 71/4 63/4 6% 61/4 6% 53/4 1/2 1/2 1/2 5% 5' 3 5' 4% 1/2 22 Note: Percolation test holes were hand dug in the bottom of backhoe pits and percolation tests were conducted on September 11, 2018. The average percolation rates were based on the last three readings of each test.