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HomeMy WebLinkAboutSoils Report 04.20.2017H-PKUMAR 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 Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 26, FOUR MILE RANCH 132 RED CLIFF CIRCLE GARFIELD COUNTY, COLORADO PROJECT NO. 17-7-259 APRIL 20, 2017 PREPARED FOR: JORDAN ARCHITECTURE ATTN: BRAD JORDAN P.O. BOX 1031 GLENWOOD SPRINGS, COLORADO 81602 (b radj ordanarc h itect @ g ma i t .co m) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS 2 - FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS . - 3 - FOUNDATION AND RETAINING WALLS - 4 - FLOOR SLABS -5- UNDERDRAIN SYSTEM - 6 - SITE GRADING - 6 - SURFACE DRAINAGE - 7 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 AND 5 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS H-Pk-KUMAR Project No. 17-7-259 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 26, Four Mile Ranch, 132 Red Cliff Circle, 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 Jordan Architecture dated March 27, 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 At the time of our study, design plans for the residence had not been developed. The building is proposed in the area roughly between the exploratory boring locations shown on Figure 1. We assume excavation for the building will have a maximum cut depth of one level, about 10 feet below the existing ground surface. For the purpose of our analysis, foundation loadings for the structure were assumed to be relatively light and 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. H-P%KUMAR Project No. 17-7-259 _2 - SITE CONDITIONS The lot was vacant and free of snow at the time of our field exploration. The site is vegetated with sage brush, grass and weeds. The ground surface slopes down to the west at a grade of about 7 percent in the building envelope. FIELD EXPLORATION The field exploration for the project was conducted on April 7, 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 drill rig. The borings were logged by a representative of H-P/Kumar. Samples of the subsoils were taken with 1% inch and 2 inch I.D. spoon samplers. The samplers were 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. 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 1/2 foot of topsoil consist of sandy clay to clayey sand and silt down to depths of 61 to 101/2 feet overlying relatively dense, silty sandy gravel with cobbles and boulders. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and practical drilling refusal was encountered in the deposit at Boring 2. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and finer than sand size gradation analyses. Results of swell -consolidation testing performed on relatively undisturbed drive samples of sandy clay, presented on Figures 4 and 5, generally indicate low to moderate compressibility under conditions of loading and H-P%KUMAR Project No. 17-7-259 -3 - wetting. The sample from Boring 2 at 5 feet showed a low expansion potential when wetted under light loading. 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. FOUNDATION BEARING CONDITIONS The upper sandy clay sand and silt soils generally have low bearing capacity and variable settlement heave/potential, mainly when wetted. The underlying relatively dense silty sandy gravel and cobble soils have relatively high bearing capacity and low settlement potential. A shallow foundation placed on the clay, sand and silt and soils will have a risk of movement if the soils become wetted. Extending the bearing level down to the relatively dense granular soils, such as with a basement excavation or piers should achieve a low settlement risk foundation. Care should be taken in the surface and subsurface drainage around the house to prevent the soils from becoming wet. It will be critical to the long term performance of the structure that the recommendations for surface grading and drainage contained in this report be followed. The amount of settlement, if the bearing soils become wet, will mainly be related to the depth and extent of subsurface wetting. Presented below are recommendations for shallow spread footings. If a deep foundation such as piers is proposed, we should be contacted for additional recommendations. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the assumed construction, we recommend the building be founded with spread footings bearing on the natural soils with a risk of settlement and distress as described below. 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 H-Pk-KUMAR Project No. 17-7-259 -4 - settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Additional settlements of to 1 inch could occur if the bearing soils are wetted. Footings that extend down to the relatively dense granular soils can be designed for an allowable soil bearing pressure of 3,000 psf with a low settlement potential. 2) The footings should have a minimum width of 16 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 heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 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 undisturbed natural soils or the relatively dense granular soils. Expansive clay soils may need to be removed down to granular 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 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. H-Pt-KUMAR Project No. 17-7-259 -5 - 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. Use of a relatively well graded granular soil such as road base as backfill will help to reduce the settlement potential. 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 325 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 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. There is a potential for differential settlement of the slab if the bearing soils become 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 H-P-KUMAR Project No. 17-7-259 -6 - 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 granular soils devoid of vegetation, topsoil and oversized rock. The clay soils could be expansive when compacted and should not be used as backfill below slabs. 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 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. 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. SITE GRADING We assume the cut depths for a basement level or site grading will not exceed about 8 to 10 feet. Embankment fills should be compacted to at least 95% of the maximum standard Proctor density near optimum moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing all vegetation and topsoil and compacting to at least 95% of the maximum standard Proctor density. The fill should be benched into slopes that exceed 20% grade. H-P%KUMAR Project No. 17-7-259 -7 - Permanent unretained cut and fill slopes should be graded at 2 horizontal to 1 vertical or flatter and protected against erosion by revegetation or other means. 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. 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 finer graded 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. 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 H-P%KUMAR Project No. 17-7-259 -8 - 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 KUMAR •G�� Louis Eller Reviewed by: Steven L. Pawlak, 22 2 LEE/ksw H-P%KUMAR Project No. 17-7-259 BUILDING ENVELOPE 50 0 50 100 APPROXIMATE SCALE -FEET 17-7-259 m4ROON DRIVE H-P:k4KUMAR LOCATION OF EXPLORATORY BORINGS Fig. 1 0 5 10 - 15 - 20 17-7-259 BORING 1 EL. 100' t 18/12 WC=12.1 DD=115 40/12 WC=4.7 DD=104 -200=58 15/6,37/6 28/6,50/6 H-P%-KUMAR BORING 2 EL. 105' 28/12 , WC=12.0 D0=105 34/12 WC=5.6 DD=111 LOGS OF EXPLORATORY BORINGS 5 10 15 20 w w x 1- w Fig. 2 LEGEND -z- TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN. / FI CLAY (CL); SANDY, VERY STIFF, SLIGHTLY MOIST, DROWN, SLIGHTLY CALCAREOUS, LOW TO SII MEDIUM PLASTICITY. SAND AND SILT (SM -ML); SLIGHTLY CLAYEY, SLIGHTLY GRAVELLY, MEDIUM DENSE, SLIGHTLY MOIST, BROWN. SAND, GRAVEL AND COBBLES (SM -GM); BASALT BOULDERS, SILTY, DENSE, SLIGHTLY MOIST, MIXED BROWN. RELATIVELY UNDISTURBED DRIVE SAMPLE; 2 -INCH I.D. CALIFORNIA LINER SAMPLE. n DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/B INCH I.D. SPLIT SPOON SAMPLE, ASTM D-1586. 18/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 18 BLOWS OF A 140 -POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES. PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 7, 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 MEASURED BY HAND LEVEL AND REFER TO BORING 1 AS 100' ASSUMED. 4. THE EXPLORATORY BORING 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 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). 17-7-259 H -P-' KUMAR LEGEND AND NOTES Fig. 3 1 ... lad ,..It, apply pny I U. Imola* SI*t, Sha Iaandi npa.I s nal M rapradwnad. •, *p1 in Irk vr} aI yl •rNlaa apprarpV D< Inane, rad Arraaklaa. Inc. Srd COngcdation I..t pulprmld In CMWrtan •'l I 17+4a/0. 17-7-259 SAMPLE OF: Sandy Clay FROM: Boring 1 ® 2.5' WC = 12.1 %, DD = 115 pcf 4.0 APPLIED PRESSURE -- KSF H -P UMAR EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 10 - T00 SWELL -CONSOLIDATION TEST RESULT Fig. 4 CONSOLIDATION - SWELL CONSOLIDATION - SWELL 1 0 — 1 — 2 —3 }h... Inlu OO' Way 1.0 wripkt I ..le4. fi. ktl:y r.p.N O., nsl b. npod.4. naWk fLIL .Mocl t...dgm 1ppaN of K.tngr any ll. .aU.. Fx. S..A Cenw:dyfinn (.31 O afi.dd in emereene. riu 17-7-259 SAMPLE OF: Sandy Clay FROM: Boring 2 @ 2.5' WC = 12.0 %, DD = 105 pcf NO MOVEMENT UPON WETTING 1.0 APPLIED PRESSURE — KSF 1 10 I00 SAMPLE OF: Sandy Clay FROM: Boring 2 © 5' WC = 5,6 %, DD = 111 pcf • lam— EXPANSION UNDER CONSTANT PRESSURE UPON WETTING L0 APPLIED PRESSURE — KSF 10 100 H-PtiKUMAR SWELL -CONSOLIDATION TEST RESULT Fig. 5 TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 17-7-259 SAMPLE LOCATION NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITY (pcf) GRADATION PERCENT PASSING NO. 200 SIEVE ATTERBERG LIMITS SOIL TYPE BORING DEPTH (ft) GRAVEL (°%) SAND (%) — LIQUID LIMIT (%) UNCONFINED PLASTIC 1 COMPRESSIVE INDEX STRENGTH (%) (PSD 1 21/2 12.1 115 Sandy Clay 5 4.7 104 58 Very Sandy Silt 2 21/2 12.0 105 Sandy Clay 5 5.6 111 Sandy Clay