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Home My WebLink AboutSubsoil StudyH G WAW# h HEPWORTH-PAWLAK GEOTECHNICAL Hepworth-Pawlak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970-945-798$ Fax: 970-945-8454 email: hpgeor?)hpgeorech.com SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT A5, ASPEN GLEN GARFIELD COUNTY, COLORADO JOB NO. 115 568A DECEMBER 24, 2015 PREPARED FOR: CARBONDALE GLEN LOT A5, LLC ATTN: RICK SALVATO 14225 VENTURA BOULDEVARD, SUITE 100 SHERMAN OAKS, CALIFORNIA 91423 (rjsaly@aol.cn' . ) Parker 303-841-7119 0 Colorado Springs 719-633-5562 ® Silverthome 974-468-1989 TABLE OF CONTENTS FIGURE PURPOSE AND SCOPE OF STUDY............................................................................- 1 - PROPOSED CONSTRUCTION.................................................................................... - 1 - SITE CONDITIONS - 2- SUBSIDENCE POTENTIAL - 2- FIELD EXPLORATION................................................................................................. - 3- -SUBSURFACE SUBSURFACE CONDITIONS......................................................................................- 3- -DESIGN DESIGN RECOMMENDATIONS 4- FOUNDATIONS........................................................................................................ - 4- FLOORSLABS .......................................................................................................... - 5 - UNDERDRAINSYSTEM..........................................................................................- 5- SURFACE DRAINAGE............................................................................................. - 6- -LIMILIMITATIONS ............................................................................................................... - 6- -REFETATIONS REFERENCES RENCES................................................................................................................ - - 8- FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - GRADATION TEST RESULTS PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at lot A5, Aspen Glen, 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 Carbondale Glen Lot A5, LLC dated December 8, 2015. Chen -Northern, Inc. previously conducted geotechnical engineering studies for the Aspen Glen development and presented their findings in reports dated December 20, 1991 and May 28, 1993, Job No. 4 112 92. 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 The proposed residence will be one and two story wood frame construction with an attached garage. Ground 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 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. Job No. 115 568A -2 - SITE CONDITIONS The vacant lot is located on River Bend Drive on the eastern end of the subdivision. Vegetation consists of grass and weeds. The site is located on a topographic bench just above the Roaring Fork River flood plain. The ground surface is relatively flat with a slight slope down to the south. The Roaring Fork River is located about 75 feet south of the building envelope. 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/siltstone and limestone with some massive beds of gypsum. 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 studies in the area, several broad subsidence areas and smaller size sinkholes were observed scattered throughout the Aspen Glen development (Chen -Northern, Inc. 1991 and 1993). These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork River valley. The lot is not located within a broad subsidence area and existing sinkholes were not observed in the immediate area of the subject lot. The nearest mapped broad depression is 1800 feet northwest and the nearest mapped sinkhole is 2200 feet west of the site. No evidence of cavities was encountered in the subsurface materials; however, the exploratory borings were relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence on Lot A5 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 Job No. 115 568A 011-M. t -3 - 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 December 9, 2015. 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 Hepworth-Pawlak Geotechnical, Inc. 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 6 to 12 inches of topsoil consist of 11/z to 2'/2 feet of gravelly silty sand overlying silty sandy gravel with cobbles and small boulders down to the maximum depth explored, 11 feet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of gradation analyses performed on Job No. 115 568A !L� small diameter drive samples (minus IV2 inch fraction) of the coarse granular subsoils are shown on Figure 4. The laboratory testing is summarized in Table 1. Free water was encountered in Boring 2 at 8 feet during the time of drilling and at 6 feet when checked two days later. No water was encountered in Boring 1. The upper subsoils were slightly moist to moist. 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 granular soils. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of 2,500 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 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 10 feet. Foundation walls acting as retaining structures should also be Job No. 115 568A -5 - designed to resist a lateral earth pressure corresponding to an equivalent fluid unit weight of at least 45 pcf. 5) All topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened and compacted. If water seepage is encountered, the footing areas should be dewatered before concrete placement. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. 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 granular soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM An underdrain should not be needed for the proposed slab -on -grade floor construction. Job No. 115 568A 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 6 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. LMTATIONS 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 Job No. 115 568A -7 - 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, HEPWORTH - PAWLAK GEOTECHNICAL, INC. Louis E. Eller Reviewed by: Daniel E. Hardin, P.E. LEE/ljf cc: KA Designworks - Ken Adler (ken@ka-designworks.com) KA Designworks - Carrie Miller (carrie@ka-designworks.com) Janckila Construction - Brett Byman (brett@janckilaconstruction.com) Job No. 115 568A REFERENCES Chen -Northern, Inc., 1991, Preliminary Geotechnical Engineering Study, Proposed Aspen Glen Development, Garfield County, Colorado, prepared for Aspen Glen Company, dated December 20, 1991, Job No. 4 112 92. Chen -Northern, Inc., 1993, Geotechnical Engineering Study for Preliminary Plat Design, Aspen Glen Development, Garfield County, Colorado, prepared for Aspen Glen Company, dated May 28, 1993, Job No. 4 112 92. Job No. 115 569A Gtech LEGEND: ® TOPSOIL; organic sandy silt and clay, firm, moist, dark reddish brown. SAND (SM); silty, gravelly, dense, slightly moist, brown. o GRAVEL AND COBBLES (GM -GP); sandy, slightly silty, probable small boulders, dense, slightly moist to wet with depth, brown. Relatively undisturbed drive sample; 2 -inch I.D. California liner sample. Drive sample; standard penetration test (SPT), 1 3/8 inch I.D. split spoon sample, ASTM D-1586. 49/12 Drive sample blow count; indicates that 49 blows of a 140 pound hammer falling 30 inches were required to drive the California or SPT sampler 12 inches. 0,2 Free water level in boring and number of days following drilling measurement was taken. IMIndicates slotted PVC pipe installed in boring to depth shown. TPractical drilling refusal. NOTES: 1. Exploratory borings were drilled on December 9, 2015 with 4 -inch diameter continuous flight power auger. 2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory borings were obtained by interpolation between contours shown on the site plan provided and checked by instrument level. 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 transitions may be gradual. 6. Water level readings shown on the logs were made at the time and under the conditions indicated. Fluctuations in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content (%) +4 = Percent retained on the No. 4 sieve -200 = Percent passing No. 200 sieve 115 568A�;� LEGEND AND NOTES Figure 3 Z-14.07 k-Z-:M