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HomeMy WebLinkAboutSoils Report 05.23.2017H 'KUMAR 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: Parker, Glenwood Springs, and Silverthorne, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 19, CEDAR HILLS 4261 COUNTY ROAD 214 GARFIELD COUNTY, COLORADO PROJECT NO. 17-7-327 MAY 23, 2017 PREPARED FOR: GABE BRUBACHER 516 HONEYSUCKLE DRIVE NEW CASTLE, COLORADO 81647 (gbrubachergmail.com) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 FOUNDATION AND RETAINING WALLS - 4 FLOOR SLABS -5- UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 6 - SEPTIC DISPOSAL AREA - 6 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4, 5 AND 6 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS H-P-KUMAR Project No. 17-7-327 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on lot 19, Cedar Hills, 4261 County Road 214, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Gabe Brubacher dated April 18, 2017. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification, compressibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recommendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION iciA4 acfuA I I A wawl Spa 6e. ovw The proposed residence will be a two story structure above a basement. Ground floor will be slab -on -grade. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 8 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS There is an existing shed on the property located as shown on Figure 1. Vegetation consists of grass and weeds. The ground surface slope is moderate down to the south. A pond is located east of the building area and an irrigation ditch is located to the northeast. H-P-KUMAR Project No. 17-7-327 -2 - FIELD EXPLORATION The field exploration for the project was conducted on April 21, 2017. Two exploratory borings were drilled in the building area and one profile boring was drilled in the general septic disposal area at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4 inch diameter continuous flight augers powered by a truck -mounted drill rig. The borings were logged by a representative of H-P/Kumar. Samples of the subsoils were taken with a 2 inch I.D. spoon sampler. The sampler was driven into the subsurface materials at various depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the. standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils and hardness of the bedrock. Depths at which the samples were taken and the penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils, below about 6 inches of topsoil, consist of sandy to very sandy silty clay overlying claystone/sandstone bedrock at depths of about 16 to 18 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density, percent finer than sand size gradation analyses, Atterberg limits and unconfined compressive strength. Results of swell -consolidation testing performed on relatively undisturbed drive samples of the sandy clay, presented on Figures 4, 5 and 6, indicate low to moderate compressibility under conditions of loading and wetting. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist to moist. H -P- KUMAR Project No. 17-7-327 -3 - DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, on the natural soils. we recommend the building be founded with spread footings bearing The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural soils should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. There could be about 1/2 to 1 inch of additional settlement if the bearing soils are wetted and precautions should be taken to prevent wetting. 2) The footings should have a minimum width of 18 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this area. 4) 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 also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) The topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the undisturbed natural soils. The exposed soils in footing area should then be moistened and compacted. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. H-PvKUMAR Project No. 17-7-327 -4 - FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting of the on-site soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least 95% of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 300 pcf. The coefficient of friction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will H-PvKUMAR Project No. 17-7-327 -5 - occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. 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 at least 50% retained on 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 the area and where there are clay soils 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 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 or sump and pump. Free -draining granular material used in the H-P-KUMAR Project No. 17-7-327 -6- 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/ feet deep and covered by filter fabric. SURFACE DRAINAGE Positive surface drainage is an important aspect of the project to prevent wetting of the bearing soils. 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. 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 paved areas. Free -draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site soils to reduce surface water infiltration. 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 foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by irrigation. SEPTIC DISPOSAL AREA Soils encountered at the Profile Boring indicate they should be feasible for an onsite wastewater treatment system. Site specific testing should be conducted for the disposal system design. KUMAR Project No. 17-7-327 -7 - 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 express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings drilled 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 borings 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 so that 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. Respectfully Submitted, H -P KUMA 41. i J.rt o"ca n o . k ma :2i [;.iPI ; Zt David A. Young, P.E. ' — -'-- 4.60 # * ' '01 A'! :.... Lip.zb Reviewed by: ` 9'du 4'4441 0. 04 Steven L. Pawlak, P.E. A—y/kac H-PKUMAR Project No. 17-7-327 r;1_ \4y 1 i i Ditch Easement f/ / /f ?0' Wide , r' 1 f'� 1 / / Lot 19 50° E +L 531.53' GP+L 55 L .,L r L Well Access Easement 2D' YVide +� *OK r L 552.51' Plat Plan Stale:1 •20' Existing YVeI :arL .,L��• L r!L .!L NlL. °a L 0 rL rL O APPROXIMATE SCALE -FEET rn LOCATION OF EXPLORATORY BORINGS 17-7-327 ✓ - w w w a w w 0 BORING 1 BORING 2 PROFILE BORING -ter � •• -1/ / // // 9/12 /•. /.. / 17/12 / DDW8.0 = =105 / / 5 //I 7/12 //7 8/12 /--• •1 WC=13.2 / WC=11.1 f / DD=113 // DD=113 / / -200=50 / / / / / / / / 10 f/,• 6/12 /�J 7/12 WC=14.7 WC=12.6 // DD=109 // DD=113 / -200=62 / // UC=1,300/ / / // / / 15 //I 6/12 //114/12 / � / r f / / �/ Pi / f —20 20/6, 50/2 50/1 9/12 WC=15.9 DD=107 -200=63 LL=28 PI=12 0 5- 10 — 10 — 15 20 -- 25 25 •----- 1- w 0 w w 17-7-327 H -P KUMAR LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND f TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN. CLAY (CL); SANDY TO VERY SANDY, SCATTERED GRAVEL, SILTY, MEDIUM STIFF TO STIFF, MOIST TO VERY MOIST WITH DEPTH, BROWN. CLAYSTONE/SANDSTONE BEDROCK; HARD TO VERY HARD, MOIST, GRAY. RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE. 7/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 7 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 21, 2017 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM BUILDING CORNERS STAKED BY OTHERS. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF THE EXPLORATORY BORINGS ARE PLOTTED TO DEPTH. 4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140); LL = LIQUID LIMIT (ASTM D 4318); PI = PLASTICITY INDEX (ASTM D 4318); UC = UNCONFINED COMPRESSIVE STRENGTH (psf) (ASTM D 2166). 17-7-327 H-P%KUMAR LEGEND AND NOTES Fig. 3 CONSOLIDATION - SWELL 0 — 2 — 3 — 4 — 5 17-7-327 10 APPLIED PRESSURE - KSF H-P�KUMAR 10 SWELL -CONSOLIDATION TEST RESULTS 100 Fig. 4 3u SAMPLE OF: Sandy Silty Clay FROM: Boring 1 (D 5' WC = 13.2 %, DD = 113 pcf � ,-- �'-- ADDITIONAL UNDER DUE CONSTANT TO COMPRESSION WETTING PRESSURE .. _.__,...—...�— rt •. .. _ ... _ _ - _ -_ .... _.. —..— _ .. -i... - l— Those teat raaune oPapplyh to the !ample. NSW. the Noting report red shall not he repi.ced, cpt in ilia without the written approval of Kumar and Aeeoclatoa, Inc. Swell Consolidation testing performed in !accordance with ASM 0-4546. 17-7-327 10 APPLIED PRESSURE - KSF H-P�KUMAR 10 SWELL -CONSOLIDATION TEST RESULTS 100 Fig. 4 3u 1 0 1 J —2 W rn 3 z 0 O —-4 J O to z 0 o —5 — 6 — 7 17-7-327 1.0 APPLIED PRESSURE - i(SF H -P- KU MAR 10 SWELL—CONSOLIDATION TEST RESULTS 100 Fig. 5 SAMPLE OF: Sandy Silty Clay FROM: Boring 2 © 2.5' WC = 8.0 %, DD = 105 pcf y �--'1 ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING __ _�...._ l upe oPPWY Y to Theo lnrea .rrpt.. (eged. The tooting report ehoO net be rep W ood....Ft re tutl. a thout the written Oppro.ul of Komar end M.oelnl... Inc. ..If ZZolOUOM1 I..b pOriprmed in pccordonc..kh AS[Y O-40$ 17-7-327 1.0 APPLIED PRESSURE - i(SF H -P- KU MAR 10 SWELL—CONSOLIDATION TEST RESULTS 100 Fig. 5 2 1 S n� a. a€ CONSOLIDATION - SWELL 0 — 2 3 — 4 — 5 — 6 17-7-327 1.0 APPLIED PRESSURE -- ILSF H-P-KUMAR I0 SWELL—CONSOLIDATION TEST RESULTS Fig. 6 SAMPLE OF: Sandy Silty Clay FROM: Boring 2 ® 10' WC = 12.6 %, DD = 113 pcf ,..— EXPANSION UNDER CONSTANT PRESSURE UPON WETTING _ _ __ _ J.. _ _ __ t .__..__..— ____ - -.__-- ____..i._ - -- .... w — -'^ - — --• - - a..— ._._. }hen telt rrnlla .ppy .ny to Ab. . 4SM.p np.r! aempl.� S..I. - 'I.' ,hotl no! M ,...,,tz • ..uyt In Ku waneut (4, rttten Inc 5..i oT Yuen. and N,odeln• k, .Sod Connfd(Yee I.rtinp rye•rk,rn0 in od.no..1th xSThI o -00 -spa. �.. 17-7-327 1.0 APPLIED PRESSURE -- ILSF H-P-KUMAR I0 SWELL—CONSOLIDATION TEST RESULTS Fig. 6 H-P�INMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-327 SAMPLE LOCATION NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITY (Pef) GRADATION PERCENT PASSING NO. 200 SIEVE ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (PSF) SOIL TYPE BORING DEPTH (ft) GRAVEL (%) SAND (%) i LIQUID LIMIT (%) PLASTIC INDEX {n4,) 1 5 13.2 113 Sandy Silty Clay 10 14.7 109 62 1,300 Very Sandy Silty Clay 2 21/2 8.0 105 Sandy Silty Clay 5 11.1 113 50 Very Sandy Silty Clay 10 12.6 113 Sandy Silty Clay Profile Boring 5 15.9 107 63 28 12 Silty Clay Loam