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HomeMy WebLinkAboutSoils Report for Foundation Design & Perc Testing 10.12.2018PKUMAR 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 12, 2018 Tito Montes c/o Palomino Design Build Attn: Jack Palomino 919 Palmer Avenue Glenwood Springs, Colorado 81601 jackpalomino55@gmail.com Subject: RECEIVED NAR ;12 2019 CIVGARFIELD cOMMlJNITY DEVELOPMENT Project No.18-7-532 Subsoil Study for Foundation Design and Percolation Testing, Proposed Residence, TBD Highway 6, Canyon Creek, Garfield County, Colorado Dear Mr. Montes: 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 August 15, 2018. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. We previously reviewed potential geologic hazard impacts on this site as described in our letter report dated August 27, 2018, Project No. 18-7-532. Proposed Construction: The proposed 1,900 square foot residence will be located on the site in the area of Pits 1 and 2, shown on Figure 1. There will be an attached 500 square foot garage. Ground floors are proposed to be slab -on -grade. Cut depths are expected to range between about 2 to 5 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 in the eastern part of the site. 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 site is mostly open grass field with apple trees along the northern property line. There are reeds and cattails along the ditch at the south property line. The lot is moderately sloping at about 10 percent down to the southwest. A drainage ditch is located along the western -2 - property line. There is an existing water well in the northwest corner of the lot. There is an existing shed in the northeast corner of the property. 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 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about 1/2 to 1 foot of topsoil, consist of mostly medium dense, silty sand with gravel and cobbles down to the maximum depth explored, 8 feet. Dense, sandy gravel with cobbles was encountered at 3 feet in Profile Pit 2 on the east side of the site. Refusal to backhoe digging was encountered in the dense gravel at 5 feet. Results of swell -consolidation testing performed on relatively undisturbed samples of the silty sand, presented on Figures 3 and 4, indicate low compressibility under existing moisture conditions and light loading and a moderate collapse potential (settlement under constant load) when wetted. The samples were moderately compressible under increased loading after wetting. Results of a gradation analysis performed on a sample of silty gravelly sand (minus 3 -inch fraction) obtained from the house 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 to moist. Foundation Recommendations: A low settlement risk foundation would be to extend the bearing level down to dense river gravel which is expected to underlie the alluvial fan soils at this site. If a deep foundation is desired, additional subsurface exploration will be needed to develop design recommendations. Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, spread footings placed on the undisturbed natural soil designed for an allowable soil bearing pressure of 1,500 psf can be used for support of the proposed residence with a risk of settlement. The soils tend to compress after wetting and there could be post -construction foundation settlement of around 1 to 2 inches depending on the depth and extent of wetting. Care should be taken to prevent wetting of the subgrade soils as described in the Surface Drainage section of this report. Footings should be a minimum width of 20 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. The exposed undisturbed natural soils should then be moistened and compacted. 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 heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls H-Pk4KUMAR Project No. 18-7-532 -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 the on-site soil 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 risk of settlement if the bearing soils are wetted. 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 relatively well graded sand and gravel such as road base 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 12% 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 this 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. underdrain system. The proposed slab -on -grade main floor level should not require an If installed, 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 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. H -P: KUMAR Project No. 18-7-532 -4 - Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation of the 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 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 (if any) 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 residence. 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: Percolation tests were conducted on September 4, 2018, 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 and the USDA gradation test results shown on Figures 6 and 7 and consist of gravelly loamy sand. 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 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 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, H-P�KUMAR Project No. 18-7-532 5 - 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 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 11411111,_ Danie E. ardin, Reviewed by: Steven L. Pawlak DEH/kac attachments 24 • Figure 1 — Location of Exploratory Pits Figure 2 — Logs of Exploratory Pits Figures 3 and 4 - Swell -Consolidation Test Results Figure 5 — Gradation 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. 18-7-532 ± 500' TO __ LEWIS LOOP co I z GRAVEL DRIVEWAY PIT 2 PROPOSED RESIDENCE AREA 1 BENCHMARK ELEVATION TOP i OF WELL CASING = 100' i I PIT 1 1 e PRCIFII F Pr I L-1 PERC 1 PERC 2 ' PERC 3 I , PROFILE PIT 2 20 0 20 40 APPROXIMATE SCALE—FEET EXISTING SHED 18-7-532 HH-P-v5KUMAR LOCATION OF EXPLORATORY PITS Fig. 1 1- w LJ L_ d LJ 0 0 5 10 LEGEND PIT 1 EL. 99' WC=3.2 DD=98 WC=6.9 DD=89 -200=18 PIT 2 EL. 93.5' WC=6.6 DD=97 1 WC=9.5 I +4=18 -200=33 PROFILE PIT 1 EL. 95' PROFILE PIT 2 EL. 97' GRAVEL=23 --1 SAND=48 SILT=19 CLAY=10 GRAVEL=51 -I SAND=38 SILT=8 CLAY=3 TOPSOIL; ORGANIC SAND, SILTY, CLAYEY, LOOSE, SLIGHTLY MOIST, DARK BROWN. SAND (SM): SILTY WITH GRAVEL AND COBBLES, MEDIUM DENSE, SLIGHTLY MOIST TO MOIST, REDDISH BROWN, SUBANGULAR ROCK. GRAVEL (GM): SANDY, SILTY, WITH COBBLES, DENSE, SLIGHTLY MOIST, RED. HAND DRIVEN 2 -INCH DIAMETER LINER SAMPLE. DISTURBED BULK SAMPLE. t PRACTICAL REFUSAL TO DIGGING WITH BACKHOE. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON SEPTEMBER 4, 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 MEASURED BY HAND LEVEL AND REFER TO THE BENCHMARK ON FIG. 1. 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); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); -200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140); 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 0 5 10 - 18-7-532 H -P- I<UMAR LOGS OF EXPLORATORY PITS Fig. 2 —12 —14 Puma left results appy. only to Me Ipmpfe> tested. The teltioq ,oilerl Ince not Ce repedJCed, e.Cepl �n lull, .ilhoul I. written opprorol of Kutner old Hseeieles, SIC. Sr.N Calselidafen tell;nQ pefforrned in oecadtnce Lin ASTM D-4546 1 SAMPLE OF: Silty Sand FROM: Pit 1 0 2' WC = 3.2 %, DD = 98 pcf 1.0 APPLIED PRESSURE - KSF 10 ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 100 18-7-532 H-PtiKUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 3 —6 z 0 1- a J —8 0 V) z 0 —10 —12 —14 trete teat results copy PAII, CO Vitt samaras tested The lest0h report 'holt not he reproduced, ss -sal m fall. without the written approval of Sumo. and Associates, Inc. Swell Caneoydoilee ternTpe worried m accardence we[h ASAH 0-4546. SAMPLE OF: Silty Sand FROM: Pit 2 0 2.5' WC = 6.6 %, DD = 97 pcf 1.0 APPLIED PRESSURE - 10 ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 100 18-7-532 H-PtiKUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 4 GRAVEL FINE 1 COARSj GRADATION TEST RESULTS H -P- KUMAR HYDROMETER ANALYSIS SIEVE ANALYSIS TINE READINGS 24 HRS 7 HRS /.� 40 100 i5 MIN 15 PAIN SOWN 19NIN 1PAIN IINN /200 1100 i „IR ___j. �._/,1,�lIZ.._�4——..?/01-.3�( II fP U.S. STANDARD SERIES CLEAR SQUARE QPSNINGS 90 T" 80 70 i 60 P. 50 8 IC 40 30 20 10 I 0 1 I 111 t 1 1 1 .1...1 111.L— 1_._L.A. 1111 —_J.. 1�._1j..u.iJ I._..1 t I .1.I.t11 1 too .001 .002 .005 ,004 .019 .037 .075 .155 .300 i1 .600 1.16 212 .36 4.78 9 4 19 36.1 76.2 727 204, 152 DIAMETER OF PARTICLES IN MILLIMETERS ii707.0.0 10 20 30 ro 30 S` 8 60 70 90 1 CLAY TO SILT SAND FINE MEDIUM COARSE GRAVEL 18 % LIQUID LIMIT SAMPLE OF: Silty Gravelly Sand SAND 49 % PLASTICITY INDEX SILT AND CLAY 33 % FROM: Plt 2 0 4-5' COBBLES These 1651 results apply only to the samples which were tested. The Inslln5 report shall not be reproduced, except In full, without the written approval of Kumar & Associates, Inc. Slave analysis texIing Is perfarmnd In accordance with ASWM D422, ASTM C136 and/or ASTM D1140. 18-7-532 Fig. 5 PERCENT RETAINED 10 20 30 4U 50 60 70 60 90 100 .001 .002 .005 .009 .019 .045 .106 .025 .500 1.00 2.00 4.75 9.5 19.0 37.5 76.2 152 203 DIAMETER OF PARTICLES IN MILLIMETERS CLAY I SILT SWJ0 V. FINE FINE J ME[IRiM 1 COARSE 1V. COARSE GRAVEL 23 % SAND 48 % GRAVEL I SMALL 1 MEDIUM 1 LARGE iE COBBLES SILT 19 % CLAY 10 % USDA SOIL TYPE: Gravelly Loamy Sand FROM: Profile Pit 1 @ 2-3' 100 90 80 70 GO 50 40 30 20 10 0 PERCENT PASSING 18-7-532 H-P%-KUMAR USDA GRADATION TEST RESULTS Fig. 6 ' HYDROMETER ANALYSIS J SIEVE ANALYSIS1 TIME READINGS U.S. STANDARD SERIES CLEAR SOUAAE OPENINGS 14 HR. 7 H 1MIN. 5 MIN. 15 MIN. 56MIi1. MIN. 4 MK 4200 4100 #50 #30 416 #8 #4 3/8' 3/4' 1 l/2' 3' 5' 6' 8 /".............1 . I .002 .005 .009 .019 .045 .106 .025 .500 1.00 2.00 4.75 9.5 19.0 37.5 76.2 152 203 DIAMETER OF PARTICLES IN MILLIMETERS CLAY I SILT SWJ0 V. FINE FINE J ME[IRiM 1 COARSE 1V. COARSE GRAVEL 23 % SAND 48 % GRAVEL I SMALL 1 MEDIUM 1 LARGE iE COBBLES SILT 19 % CLAY 10 % USDA SOIL TYPE: Gravelly Loamy Sand FROM: Profile Pit 1 @ 2-3' 100 90 80 70 GO 50 40 30 20 10 0 PERCENT PASSING 18-7-532 H-P%-KUMAR USDA GRADATION TEST RESULTS Fig. 6 PERCENT RETAINED f 24H0. 045 AWL 10 20 30 40 50 60 70 80 90 HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS 7 HR 15 MN1. 61MN. f91AIN. 4 MIN. U.S, STANDARD SERIES 1 CLEAR SQUARE OPENINGS 1 MIN. #325 #140 #60 #35 #18 #10 #4 318' 3/4' 1 1 ? 3' 5' 6' 8" 100 100 .001 .002 .005 .009 .019 .045 CLAY SILT .106 .025 .500 1.00 2.00 4.75 9.5 19.0 37.5 76.2 152 203 DIAMETER OF PARTICLES IN MILLIMETERS SAND GRAVEL V. FIRE FRJE M€OLIM i COARSE IV. COARSE SMALL MEDIUM LARGE COBBLES GRAVEL 51 % SAND 38 % SILT 8 % CLAY 3 % USDA SOIL TYPE: Very Gravelly Sand FROM: Profile Pit 2 @ 3-4' 90 60 70 60 50 40 30 20 10 0 PERCENT PASSING 18-7-532 H-PMKIJMAR USDA GRADATION TEST RESULTS Fig. 7 H-P�KUMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS SAMPLE LOCATION PIT 1 2 Profile Pit 1 DEPTH (ft) 2 6 2'/2 4-5 2-3 NATURAL MOISTURE CONTENT (%) 3.2 6.9 6.6 9.5 NATURAL DRY DENSITY (pcf) 98 89 97 Project No.18-7-532 GRADATION GRAVEL (%) 18 SAND (%) 49 PERCENT PASSING NO. 200 SIEVE 18 33 Profile Pit 2 3-4 USDA SOIL TEXTURE GRAVEL (%) SAND (%) SILT (%) CLAY (%) 23 48 19 10 51 38 8 3 SOIL TYPE Silty Sand Silty Sand Silty Sand Silty Gravelly Sand Gravelly Loamy Sand Very Gravelly Sand JI1,7d/....IN TABLE 2 PERCOLATION TEST RESULTS PROJECT Nn 11:1_7_5R9 HOLE NO. Perc 1 HOLE DEPTH (INCHES) Perc 2 Perc 3 32 311/2 28 LENGTH OF INTERVAL (MIN) 10 10 10 WATER WATER DROP IN DEPTH AT DEPTH AT WATER START OF END OF LEVEL INTERVAL INTERVAL (INCHES) (INCHES) (INCHES) 5 AVERAGE PERCOLATION RATE (MIN./INCH) 41/2 1/2 41/2 41/8 41/ 33/4 3% 31/2 1/4 31/2 31/4 31/4 3 1/4 1/4 Water added 5 41/2 1/2 41/2 41/ 41/ 3'/8 1/4 3'/3 35/ 1/4 35/ 31/4 3 31/4 5 3 41/4 1/4 3/4 41/4 35/ 5/5 3% 3%3 1/2 53/4 53/8 ' 5' 43/4 43/4 5/8 41/4 1/2 40 34 20 Note: Percolation test holes were hand dug in the bottom of backhoe pits. Percolation tests were conducted on September 4, 2018. The average percolation rates were based on the last three readings of each test.