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HomeMy WebLinkAboutSoils Report 04.28.2017H-PKUMAR Geotechnical Engineering f 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 Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE 3808 DRY PARK ROAD GARFIELD COUNTY, COLORADO JOB NO. 17-7-201 APRIL 28, 2017 PREPARED FOR: CRYSTAL RIVER RANCH CO, LLP c/o WOODSTONE INC. ATTN: SHERRY WILLIAMS 6801 EAST SOPRIS CREEK ROAD SNOWMASS, COLORADO 81654 (sherry@woodstoneinc.net ) 4ECEIV )` JUL 2 4 2017 GAREIEW COUNTY )IMMUNITY DEVELOPMENT TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - I - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - FIELD EXPLORATION ... - 2 - SUBSURFACE CONDITIONS - 2 - FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS - 4 - FLOOR SLABS - 4 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 5 - LIMITATIONS - 6 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS H-PkKUMAR Project No. 17-7-201 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at 3808 Dry Park Road, 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 Crystal River Ranch Co, LLP dated February 22, 2017. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils and bedrock 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 The proposed residence will be one story wood frame construction above a crawlspace and with an attached garage. Garage floor will be slab -on -grade. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 4 feet. We assume relatively Tight foundation loadings, typical of the proposed type of construction. constructed in the same general area as the previous house. The residence will be 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 The building area is located on the west (uphill) side of Dry Park Road at a previously developed area. The previous residence has been razed. An existing agricultural barn is located north of H -Pk Kt1MAR Project No. 17-7-201 -2 - the site and a residence further north. Vegetation consists of a few willow trees, grass and weeds. Gravel has been placed in the previous building area. The site is located at the bottom of an east facing hillside. The ground surface is relatively flat in the building area. Bedrock outcrops are visible on the ridgeline to the northwest. FIELD EXPLORATION The field exploration for the project was conducted on April 3, 2017. Two exploratory borings were drilled 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 CME -45B 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 LD. spoon sampler. The sampler was driven into the subsoils 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 hardncss 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 one foot of topsoil at Boring I and 3 feet of fill at Boring 2 consist of 41 to 51/2 feel of sandy silt and clay with gravel overlying siltstone/sandstone bedrock down to the maximum depth explored, 21 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content, density, and percent finer than sand size gradation analyses. Results of swell - consolidation testing performed on relatively undisturbed drive samples of the clay soils, presented on Figure 4, indicate low to moderate compressibility under conditions of loading and wetting. The laboratory testing is summarized in Table 1. H-PKUMAR Project No. 17-7-201 -3 - No free water was encountered in the borings at the time of drilling the subsoils and bedrock were moist to slightly moist with depth. FOUNDATION BEARING CONDITIONS The existing fill material from previous site development is not adequate for foundation support and should be removed from beneath proposed foundations. The underlying clay soils are suitable to support the proposed house foundation. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural soils below topsoil and fill. 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 settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. 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 a lateral earth pressure corresponding to an equivalent fluid unit weight of at least 50 pcf. H-PkKUMAR Project No. 17.7-201 -4- 5) All existing fill, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively firm 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. FOUNDATION AND RETAINING WALLS All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressure recommended above assumes 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 al 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 Targe 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. 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. Any existing fill material should be evaluated at the time of excavation for slab support. 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 H-PkKUMAR Project No. 17-7-201 -5 - 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 Tess 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 granular 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 areas with clay soils and shallow bedrock 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 retaining walls, crawlspace and basement areas (if any), 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. Free -draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, Tess 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. 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. H -P KUMAR Project No, 17-7-201 -b- 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 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 5 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, 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 H-P*KUMAR Project No. 17-7-201 -7 - 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 t KU MAR Louis Eller Reviewed by: /Cc `ir • •• `el �? �� Daniel E. Hardin, P.E. LEE/kac 2. 443 W-PItKUMAR Project No. 17-7-201 NOT TO SCALE AG BARN FUTURE 3 -BEDROOM RESIDENCE P2 h BORING 2 P1 ti EXISTING SEPTIC— Ca, TANK TO BE BORINGTO BE ABANDONED ABANDONED J ovoif N2ivd AJC TO EXISTING STA 17-7-201 H-P4KUMAR LOCATIONS OF EXPLORATORY BORINGS Fig. 1 0 - 5 - 10 - 15 - 20 - 25 - 30 BORING 1 BORING 2 16/12 / WC=15.8 r DD=109 r / -200=60 / 20/6,50/4 WC=5.4 DD=121 50/0 50/0 12/12 14/12 WC=15.9 DD=112 -200=71 50/5 50/0 0 7 5 10 15 --- -- 20- 20- 25 25 30 17-7-201 H -PKU MAR LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND wiz R X 7 z TOPSOIL; ORGANIC SANDY CLAY AND SILT, F RM, MOIST, DARK BROWN. FILL; SANDY CLAY AND SILT, MEDIUM STIFF, MOIST, BROWN. CLAY (CL); SANDY, SILTY WITH GRAVEL, MEDIUM STIFF, MOIST, REDDISH BROWN. SILTSTONE/SANDSTONE BEDROCK; HARD TO VERY HARD WITH DEPTH, SLIGHTLY MOIST, RED. MAROON FORMATION. 7 RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE. 16/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 16 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALrFORNIA SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 3, 2017 WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 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 0 2216); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). 17-7-201 H-P1KUMAR LEGEND AND NOTES Fig. 3 1 J J fit —1 z 0 —2 J 0 z —3 z 0 U CONSOLIDATION - SWELL — 4 1 — 1 — 2 — 3 — 4 —5 SAMPLE OF: Sandy Silty Clay FROM: Boring 1 © 2.5' WC = 15.8%, DD = 109 pcf —200 = 60% ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 1.0 APPLIm PRESSURE — KV' 10 100 SAMPLE OF: Sandy Silty Clay FROM: Boring 2 @ 5' WC = 15.9%, DD = 112 pcf —200 = 71% b'... k.t naso. rout .ww''. mon 1n1nt. ti,. 1I.tM15 n.1:44 Il.ol bel M erpoduc.d, abaci b Iwo .111Nv1 the .ei{Iun'D0Jma1 e1 Keno and AI.NIelia. he. 5.11 remdlsetbn C,IU..a wAmmM I a[eelaalK� .IU ASU F.5yi6, 1.0 APPLIED PRESSURE — KSS' NO MOVEMENT UPON WETTING 10 100 17-7-201 H-P41KUMAR SWELL -CONSOLIDATION TEST RESULT Fig. 4 H-PKUMAR TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-201 ( SAMPLE LOCATION NATURAL i GRADATION { ATTERBERG LIMITS UNCONFINED SOIL TYPE BORING DEPTH (;t) MOISTURE CONTENT (%) NATURAL DRY DENSITY (ocfl 1 GRAVEL 06) SAND (%) PERCENT PASSING NO. 200 SIEVE LIQUID LIMIT (%1 PLASTIC INDEX INDEX (961 COMPRESSIVE STRENGTH (PSF) 1 21/ 1 15.8 109 60 Sandy Silty Clay 5 5.4121 Sandy Silty Clay with Gravel 2 5 15.9 112 71 Sandy Silty Clay 1