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HomeMy WebLinkAboutSoils Report 05.22.2019K+A Kumar & Associates, Inc.® Geotechnical and Materials Engineers and Environmental Scientists An Employee Owned Company 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado Jai y ASSa[iatas, i4 c, 30 Y"m' 89 20 SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 54, FILING 4B OAK MEADOWS 358 SILVER KING COURT GARFIELD COUNTY, COLORADO PROJECT NO. 19-7-271 MAY 22, 2019 PREPARED FOR: IAN YOUNG 442 SILVER KING COURT GLENWOOD SPRINGS, COLORADO 81601 ityoungpainting(a�yahoo.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - GEOLOGY -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 - 8 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS FIGURE 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc. Project No. 19-7-271 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 54, Filing 4B, Oak Meadows, 358 Silver King Court, 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 proposal for geotechnical engineering services to Ian Young dated April 19, 2019. 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 were conceptual. In general, the residence will be located in the downhill, eastern part of the lot roughly between the exploratory borings shown on Figure 1. We assume excavation for the building will have a maximum cut depth of one level, up to about 10 feet below the existing ground surface. For the purpose of our analysis, foundation loadings of 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. SITE CONDITIONS The lot was vacant at the time of the field exploration. The terrain across the majority of the lot was moderately sloping down to the northeast at about 5% to 10% and was steeply sloping to the Kumar & Associates, Inc. ® Project No. 19-7-271 -2 northeast at about 25% to 30% in the uphill western part of the lot. The elevation difference across the building site is about 6 feet. Vegetation consisted of grass, weeds, and oak brush. Two story residences are north and south of the site, Silver King Court and a playground are east, and vacant land is to the west. GEOLOGY The lot is located near the lower limit of a mapped, very large, dormant landslide complex. Hepworth-Pawlak Geotechnical, Inc. evaluated the overall stability of the landslide as part of the subdivision approval by Garfield County in 1999. The evaluation included depth to bedrock and depth to groundwater level, both being relatively deep. The conclusion was that the landslide complex was not near critical stability condition and moderate cut and fill depths made for subdivision infrastructure and individual lot development should not affect the overall stability of the landslide. FIELD EXPLORATION The field exploration for the project was conducted on May 7, 2019. 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 Kumar & Associates. 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 consist of about 1'/z to 2 feet of topsoil overlying very stiff silty, sandy clay and/or Kumar & Associates, Inc. Project No. 19-7-271 -3- medium dense to dense, clayey, sandy gravel with basalt cobbles and probable boulders. Drilling in the coarse granular soils with auger equipment was difficult due to the cobbles and boulders and 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 gradation analyses. Results of swell -consolidation testing performed on relatively undisturbed drive samples of the clay and sand soils, presented on Figure 4, indicate low to moderate compressibility under conditions of loading and low expansion potential upon wetting. Results of gradation analyses performed on small diameter drive samples (minus 1 %2 inch fraction) of the coarse granular subsoils are shown on Figure 5. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of exploration and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The sandy clay soils and clayey sandy gravel and cobble soils encountered at typical shallow foundation depth have moderate bearing capacity and somewhat variable settlement/heave potential. A shallow foundation placed on the sandy clay and gravel soils should typically have a low risk of post -construction movement potential. It will be critical to the long-term performance of the structure that the recommendations for surface grading and subsurface drainage contained in this report be followed. The amount of settlement/heave, if the bearing soils become wet, will mainly be related to the depth and extent of subsurface wetting. Sub - excavation of expansive clay layers could be needed to help limit the movement potential and should be further evaluated at the time of excavation. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, the building can be founded with spread footings bearing on the natural sandy clay and gravel soils with a risk of movement. The more expansive clay soils should be sub -excavated and replaced with compacted structural fill. Kumar & Associates, Inc. Project No. 19-7.271 -4- 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 2,500 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. Additional differential movement up to about 1 inch could occur depending on the depth and extent of future wetting of the subgrade soils. 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 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 firm natural soils. Expansive clay soils should also be removed below footing bearing level as needed and replaced with structural fill such as CDOT Class 6 base course compacted to at least 98% of standard Proctor density. 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 Kumar & Associates, Inc. Project No. 19-7-271 -5- 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. Backfill should not contain topsoil or rock larger than 6 inches. 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 slightly above 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 0.40. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 350 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, can be used to support lightly loaded slab -on -grade construction with a risk of movement. The clay soils could exhibit expansion potential and Kumar & Associates, Inc. Project No. 19-7-271 6 heave the floor slab if wetted and may need to be sub -excavated at least 2 feet and replaced with compacted structural fill. If risk of movement cannot be tolerated, a structural floor over crawlspace is recommended. 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 should consist of predominantly granular soils devoid of vegetation, topsoil and oversized rock or CDOT Class 6 road base. 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 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 The risk of construction -induced slope instability at the site appears low provided the building is located in the less steep slope area as planned and cut and fill depths are limited. We assume the Kumar & Associates, Inc. Project No. 19-7-271 7 cut depths for the basement level will not exceed one level, about 10 feet. Fills should be limited to about 8 feet deep. 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 the portions of the hillside exceeding 20% grade. 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. The risk of slope instability will be increased if seepage is encountered in cuts and flatter slopes may be necessary. If seepage is encountered in permanent cuts, an investigation should be conducted to determine if the seepage will adversely affect the cut stability. This office should review site grading plans for the project prior to construction. 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 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. Kumar & Associates, Inc. ` Project No. 19-7-271 -8- 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, Kumar & Associates, Inc. Shane J. Robat, P.E. Project Manager Reviewed by: Steven L. Pawlak, P SJR/kac Kumar & Associates, Inc.. Project No. 19-7-271 LOT 55 N 87°21'16'. W 115.52` LOT 53 10 0 i 0 20 APPROXIMATE SCALE -FEET 5' Ut+fiiY OntenageW Lament; 88 19-7-271 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 EL. 6828' BORING 2 EL. 6823' n 10704V 97271-C2 Ec 0 5 10 15 20 13/12 /-/-- 18/12 / WC=16.7 DD=106 34/12 14/12 WC=12.3 DD=114 f�. 19/12 fo. 24/12 35/12 WC=9.0 +4=46 -200=26 14/12 WC=17.8 +4=15 -200=49 0 5 10 15 20 25 25 DEPTH —FEET 19-7-271 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 \locc:\?omp\Ac?ubilsh_10734\' 97271 —02 oo E LEGEND / fr TOPSOIL; ORGANIC, SILTY, SANDY CLAY WITH SCATTERED GRAVEL, STIFF, MOIST, DARK BROWN. CLAY (CL); SILTY, SANDY WITH SCATTERED GRAVEL, VERY STIFF, MOIST, BROWN. LOW TO MEDIUM PLASTICITY. GRAVEL AND COBBLES (GC—CL); SILTY, VERY SANDY CLAY MATRIX, BASALT AND SANDSTONE ROCKS, ANGULAR—SUBANGULAR, MEDIUM DENSE TO DENSE, MOIST, BROWN. DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE. IDRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST. 13/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 13 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON MAY 7, 2019 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 OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 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 D2216); DD = DRY DENSITY (pcf) (ASTM D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140). 19-7-271 Kumar & Associates LEGEND AND NOTES Fig. 3 CONSOLIDATION - SWELL CONSOLIDATION - SWELL 0 —4 0 SAMPLE OF: Sandy Clay with Gravel FROM: Boring 1 ® 2.5' WC = 16.7 %, DD = 106 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE - KSF 10 100 These test results apply only to the samples tested. The testing report shall not be reproduced. except in full. without the written approval of Kumar and Associates. Inc. Swell Consolidation testing performed in accordance with ASTM D-4546. SAMPLE OF: Clayey Sand with Gravel FROM: Boring 1 ® 10' WC = 12.3 %, DD = 114 pcf NO MOVEMENT UPON WETTING 1.0 APPLIED PRESSURE - KSF 10 100 19-7-271 Kumar & Associates SWELL —CONSOLIDATION TEST RESULTS Fig. 4 HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS 24 HRS 7 HRS 4S MIN 80MIN 19MIN 4A IN MIN 4200 U.S. /100 / STANDARD SERIES . Jr 430 / 6 41? /8 /4 CLEAR SQUARE OPENINGS 3/8" 3 4" 1 2" 3" 5"6" Iro 100 _UAW I 1 so -I--L I 10 _ 80 zo _I_- 1 r 70 I { 30 ---1I 2 60 — 40 2 p _--- — —I 1 —I_ L 50 — — -- I i r— E 40 I I -1 I 60 L_ I- I 30 1 I 70 f -I 20 I 80 11_ L — —1 10 90 —I —I _. ____ _{ o - T-T --T 7T T I 1 1 1 J-11_TI- - ItI 1 I 1 1 - A. "=J -I J 1.1.711 -_ -1 1_ I 11 J 111 100 .001 .002 .005 .009 .019 .037 .075 DIAMETER .150 .300 I .600 1.18 12.36 4.75 .425 2.0 OF PARTICLES IN MILLIMETERS __I- 9 5 19 38.1 76.2 127 152 - 200 SAND GRAVEL CLAY TO SILT FINE MEDIUM COARSE FINE COARSE COBBLES GRAVEL 46 % LIQUID LIMIT SAMPLE OF: Clayey Sandy Gravel SAND 28 % SILT PLASTICITY INDEX FROM: AND CLAY 26 % Boring 2 0 5' HYDROMETER ANALYSIS SIEVE ANALYSIS 24 HRS 45 MIN TIME READINGS 7 HRS 15 MIN 60MIN 19N N 4MIN WIN /200 U.S. STANDARD SERIES 4100 450 440 430 4 6 41? /8 / 3/8" CLEAR SOUARE OPENINGS 3 4" 1 1/2" 3" 5'6" /"0 100 -- 90 r �-- 10 I I I i 80 _ - -I I 20 1 { 70 i I 30 I I--- I B0I-.--40 I + 1 50 } - z 50 I Y I 1 I I E 40 I I I 30 --I t1T 1 70 _ 20 - - I - 80 - -I I 10 - 90 - _ -I-1 I_ I 0 - 1 1 1 17 I 1 1 1 IT 1TT - I _L- 1 T I -TT 1 - J 11 1 1T1T 1 —r—r 1 1 I I I I 1 100 .001 .002 .005 .009 _1_ .019 .037 .075 .150 .300 .425 DIAMETER OF PARTICLES .800 1.18 12.36 4.75 9 5 19 38.1 76.2 127 2.0 IN MILLIMETERS isz 200 SAND. GRAVEL CLAY TO SILT FINE MEDIUM COARSE FINE COARSE COBBLES GRAVEL 15 % SAND 36 % SILT AND CLAY 49 % LIQUID LIMIT PLASTICITY INDEX These test results apply only to the SAMPLE OF: Very Clayey Sand with Gravel FROM: Boring 2 0 10' samples which were tested. The testing report shall not be reproduced, except in full, without the written approval of Kumar & Associates, Inc. Sieve analysis testing Is performed In accordance with ASTM D6913, ASTM D7928, ASTM C136 and/or ASTM D1140. 19-7-271 Kumar & Associates GRADATION TEST RESULTS Fig. 5 C• _ C W uJ _a) co c 1.11 a co j m E v c ao c 2 N C W be 2 III Project No. 19-7-271 SOIL TYPE Sandy Clay with Gravel Clayey Sand with Gravel Clayey Sandy Gravel Very Clayey Sand with 11 Gravel UNCONFINED COMPRESSIVE STRENGTH (psf) ATTERBERG LIMITS PLASTIC INDEX (%) LIQUID LIMIT (%) PERCENT PASSING NO. 200 SIEVE N C> GRADATION a N M J g t- o .--' NATURAL DRY DENSITY (P) O '--i ---- .--i FNZ Z 0 0 5 (� vO •--� M N,—, •--, 9.0 1 00 •--� II SAMPLE LOCATION DEPTH (ft) O O BORING 4 -' N