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HomeMy WebLinkAboutSoils Report 10.18.2017H-P-� UM 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 CE GARFIELD COUNTY, COLORADO PROJECT NO. 17-7-722 OCTOBER 18, 2017 PREPARED FOR: MARY KOZIOL 2102 GRAND AVENUE GLENWOOD SPRINGS, COLORADO 81601 (info @ glenwoodsnrin gscedarlodge. com) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - SUBSIDENCE POTENTIAL 2 FIELD EXPLORATION -2- SUBSURFACE CONDITIONS- 3 DESIGN RECOMMENDATIONS - 3 FOUNDATIONS FOUNDATION AND RETAINING WALLS - 3 - 4 - FLOOR SLABS UNDERDRAINSYSTEM - 6 - SURFACE DRAINAGE - 6 - - 7 - LIMITATIONS -7- 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 H-P‘.KUMAR Project No. 17-7-722 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot A19, Aspen Glen, River's Bend, 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 Mary Koziol dated September 17, 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 expansion potential 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 Plans for the proposed residence have not been developed and we understand the findings of our study will be considered in the sale/purchase of the lot. We assume the residence will be typical of this area and consist of a 1 to 2 story structure with a basement or crawlspace and an attached garage. Ground floor could be slab -on -grade or structural above crawlspace. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 10 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. When building loadings, location and grading plans have been developed, 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 was gently sloping down to the south witharol�und 5 feet of elevation difference across the lot. Vegetation consisted of grass and weeds. H-PaKUMAR Project No. 17-7-722 -2 - SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. .+, Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, several sinkholes were observed scattered throughout the development, mostly east of the Roaring Fork River. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork River Valley. jThe closest mapped sinkhole is located about 150 feet northeast of Lot A194 Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities waencountered in the subsurface materials; however, the exploratory borings were relatively shall—oTv. for foundation design only. Based on our present knowledge of the subsurface conditions ons at the site, it cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence on Lot A19 throughout the service life of the proposed residence, in our opinion, is low; however, the owner should be made aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. FIELD EXPLORATION The field exploration for the project was conducted on October 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 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 H-P%KUMAR Project No. 17-7-722 -3 - 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'/ feet of topsoil overlying 31/2 to 6 feet of stiff, sandy silty clay with scattered gravel underlain by dense slightly silty sandy gravel and cobbles with small boulders to the maximum drille equipment was difficu borings. illing in the dense coarse granular soils with auger e cobbles and boulders with near auger drilling refusal in the Laboratory testing performed on samples obtained from the borings included natural moisture content and density and gradation analyses. Results of swell -consolidation testing, presented on Figure 4, indicate the upper clay soils have low to moderate compressibility under loading and variable minor to low settlement -heave potential when wetted under light loading. Results of gradation analyses performed on a small diameter drive sample (minus 11/2 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 drilling and the subsoils were slightly moist. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, - : •• -. , , the building be founded with spread footings bearing on the natural soils some settteme.nr nntenrtnl The expansion potential measured on the clay soil sample is conside -d an anomaly and footiugs do not need to be designed for expansive H-PtKUMAR Project No. 17-7-722 -4 - soils. Extending the bearing level down into the dense gravel soils will have a low settlement potential. 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. Footings extended down to bear entirely on the dense gravel soils can be designed for an allowable bearing pressure of 3,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less and mainly if the clay soils are wetted after construction. 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 abov earing elevation for frost protection. Placement of foundations at = oelow 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 or dense natural gravel 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. 36 inches FOUNDATION AND RETAINING WALLS Foundation walls, pool 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 H-P%KUMAR Project No. 17-7-722 -5 - 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. Backfill should not contain organics or rock larger than about 5 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 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 for clay and 0.50 for gravel. 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 H-PkKUMAR Project No. 17-7-722 -6 - 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. The clay soils should be evaluated for expansion potential at the time of excavation for possible sub -excavation and replacement with compacted granular structural fill. 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 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 the area 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 H-P%KUMAR Project No. 17-7-722 -7- a suitable gravity outlet, sump and pump or perforated sump/drywell. 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. SURFACE DRAINAGE Providing proper surface grading and drainage will be important to limiting wetting of the bearing soils below the structure. 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 5 feet from foundation walls. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at the time of this study. 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 H-P%KUMAR Project No. 17-7-722 -8- 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: KUMAR Steven L. Pawlak Reviewed by: Daniel E. Hardin, P.E. SLP/kac H-PVKUMAR Project No. 17-7-722 BUILDING ENVELOPE 0.215 ACRE BORING 1 20 0 20 40 APPROXIMATE SCALE -FEET 17-7-722 H -P- KUMAR LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 BORING 2 0 - 1 12/12 WC=16.7 50/3 13/12 DD=110 37/12 5 Li 90/12 10 WC=1.1 +4=65 I �i _ rl © -200=7 _ 15 ��JJ ` 15 0 17-7-722 H -P- KUMAR LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND -ti 7 7 • TOPSOIL; ORGANIC SANDY SILT AND CLAY, SLIGHTLY MOIST, BROWN. CLAY (CL), SILTY, SANDY, SCATTERED GRAVEL, STIFF, SLIGHTLY MOIST TO MOIST, STIFF, RED—BROWN. GRAVEL AND COBBLES (GM—GP); SLIGHTLY SILTY, DENSE, SLIGHTLY MOIST, BROWN, ROUNDED ROCK. RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE. IDRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON SAMPLE, ASTM D-1586. 13/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 13 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON OCTOBER 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 D 2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). 17-7-722 H-1)vKUMAR LEGEND AND NOTES Fig. 3 CONSOLIDATION - SWELL (%) CONSOLIDATION - SWELL 1 0 1 2 1 0 -1 -2 -3 4 SAMPLE OF: Sandy Silty Clay., FROM: Boring 1 0 2.5' WC = 12.1 %, DD = 104 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE - KSF 10 100 SAMPLE OF: Sondy Silty Clay FROM: Boring 2 0 2.5' WC = 16.7 %, DD = 110 pcf Thew bit mate a pod/ to Po ample. tested. The °tasting report Moll not 0' reproduced. except n m..alwt the unto) epprm- of Kumar p-0 Aexaulq. Im. Swll CeriN6.LLm I ..g Meme It eeee/aen0. +u APu o-.su. ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 1.0 APPLIED PRE 100 17-7-722 H P-. KUMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 4 SIEVE ANALYSIS Y5. STANDARD 5EmE2 CLEAR SQUARE OPEN0402 D 00 a 0 50 20 I0 000 .o zse �4, Is v s � 19 2'1 .425 DIAMETER OF PARTICLES IN MILLIMETERS CLAY TO SILT SAND GRAVEL FINE GRAVEL 65 X LIQUID UMIT SAMPLE OF: Slightly Silty Sandy Gravel SAND 28 X MEDIUM JCOARSE PLASTICITY INDEX FINE I COARSE SILT AND CLAY 7 X FROM: Boring 2 0 1D' 00 20 30 40 50 ea -Ll '>Q 1- 90 -- +00 127 200 52 CODDLES Thaw test results apply ny to Ih• samples widen were taste , The tenting report shall net b reproduced, except In full, without th written approval of Kumar it As isolates. Inc. Slave analysis lasting is ertonned In accordance with A311t 0422, ASPM 0136 and/or ASTM D1140. 17-7-722 H-PWUMAR GRADATION TEST RESULTS Fig. 5 Project No. 17-7-722 co ccW w W CC } r Q h W ^ E" J 0i 0 O } r 2 2 co SOIL TYPE Sandy Silty Clay Sandy Silt and Clay Sandy Silty Clay Slightly Silty Sandy Gravel UNCONFINED COMPRESSIVE STRENGTH (PSF) ATTERBERG LIMITS PLASTIC INDEX (A) LIQUID LIMIT (Vo) I PERCENT PASSING NO. 200 SIEVE N. 7 Z O Q 0 6 tr 0 0 Q ' W N y GRAVEL (%) in l0 NATURAL DRY DENSITY (pcf) 104 110 0 NATURAL MOISTURE CONTENT (%) N 8.3 N c6 z 0 Q 0 O J DEPTH (ft) 5 \ N O ^' SAMPLEI 0 2 ¢ 0 m .. N