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Home My WebLink AboutSubsoil Study for Foundation Design 11.28.14H G< tech HEPWORTH-PAWLAK GEOTECHNICAL 16�-7 3 I lep�aorth-Pawlak GeoiechnicA' Inca 5020 County Road 154 Glei Iwo(d spiint!s, C._()]OIad') 51601 Phone: 970-945,7988 Fax: 070-945.8451 entail: SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT FW -6, THE FAIRWAYS ASPEN GLEN DEVELOPMENT GARFIELD COUNTY, COLORADO JOB NO. 114 516A NOVEMBER 28, 2014 PREPARED FOR: WOODBRIDGE MORTGAGE INVESTMENTS ATTN: RICK SALVATO 22 CENTER STREET, FRONT SUITE FREEHOLD, NEW JERSEY 07728 (risa1y(&,ao1.canx) Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1959 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY.........................................................................: 1 - PROPOSED CONSTRUCTION...................................:...........................:.................. - 1 - SITECONDITIONS....................................................................................................- 2 - SUBSIDENCE -SUBSIDENCE POTENTIAL......................................................................................- 2 - -FIELFIELD D EXPLORATION..............................................................................................- 3 - SUBSURFACE -SUBSURFACE CONDITIONS................................................................................... - 3 - FOUNDATION BEARING CONDITIONS.................................................................- 4 - DESIGN - DESIGN RECOMMENDATIONS..............................................................................: 4 - FOUNDATIONS.........:............................................................................................- 4 - FOUNDATION AND RETAINING WALLS............................................................ 6 - FLOORSLABS....................................................................................... - UNDERDRAINSYSTEM.......................................................................................: 8 - SURFACEDRAINAGE..........................................................................................- 8 - LIMITATIONS - LIMITATIONS............................................................................................._.............: 9 - REFERENCES - REFERENCES............................................................................................................ 10- FIGURE 0- 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 Job No. 114 516A C�1ech PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot FW -6, The Fairways, Aspen Glen Development, west of Highway 82, 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 Woodbridge Mortgage Investment Fund 2, dated November 17, 2014. 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 This study was performed to obtain data relevant to purchase of the lot. It is likely that a residence constructed on the lot will be a one or two story structure of wood frame construction with a basement or a crawlspace with a structural floor and an attached garage. Basement and garage floors will be slab -on -grade. 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. 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. 114 516A GLCPf�Cf 1 -2 - SITE CONDITIONS The site is currently an undeveloped lot in the Aspen Glen Development. The lot is bordered to the southwest by a golf course fairway, to the northeast by Golden Bear Drive, to the northwest by an existing two story residence and to the southeast by an undeveloped lot. The lot slopes slightly down to the southwest with an elevation difference of about 1 foot across the main portion of the lot. Vegetation on the lot consists of sparse grasses and weeds. 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 sinkhole areas were observed scattered throughout the Aspen Glen development, predominantly on the east side of the Roaring Fork River (Chen -Northern, Inc., 1993). These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork River valley. The nearest sinkhole was mapped about 800 feet to the north of Lot FW -6. Sinkholes were not observed in the immediate area of the subject lot. 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 FW -6 throughout the service life of the proposed residence, in our opinion, is low; however, the owner should be made aware of the Job No. 114 516A Gk�gtec:h -3 - 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 November 20, 2014. 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 I% 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 foot of topsoil overlying 6 to 7 feet medium stiff to stiff, sandy silty clay. The clay soils were underlain by dense to very dense silty sandy gravel with cobbles from 7 to 8 feet down to the maximum depth explored of 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 in both borings. Laboratory testing performed on samples obtained from the borings included natural moisture content and density. Results of swell -consolidation testing performed on Job No. 114 516A Gtech relatively undisturbed drive samples of the clay soils, presented on Figures 4 and 5, indicate low compressibility under conditions of light loading at existing moisture contents and low expansion to high collapse (hydro -compression) under light loading and wetting (the sample indicating high collapse may have been partially disturbed during sampling thus exaggerating the collapse indicated). 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 to moist. FOUNDATION BEARING CONDITIONS The upper clay soils are variable in consistency and not suitable for support of the proposed structure. The dense granular soils underlying the clay soils are suitable for support of the proposed structure on spread footings with low risk of movement. Removal of the upper clay soils and placement of the footings on the granular soils should be feasible if a basement level is constructed. Removal of the clay soils and placement of the footings on properly compacted granular fill bearing on the underlying granular, site soils should be feasible for support of the structure if a crawlspace is designed. 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 or properly compacted structural fill. The design and construction criteria presented below should be observed for a spread footing foundation system. Job No. 114 516A HF,tecn -5- 1) Footings placed on the undisturbed natural granular soils or properly compacted structural fill 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 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) All topsoil, clay 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. 6) Structural fill in foundation areas should consist of imported granular material such as CDOT Class 6 road base placed in 8 inch maximum loose lifts and compacted to a minimum of 100 percent of the standard Proctor value for the material at a moisture content near optimum. Structural fill should extend laterally beyond the edge of the footings 1 foot for every 2 feet of fill depth with a minimum of 2 feet. Prior to placement of structural fill, the excavation should be cleaned of any clay soil or loose material and compacted. The excavation should be observed prior to placement of structural fill and the structural fill should be tested for compaction by a representative of the geotechnical engineer. Job No. 114 516A - GEcPteCh 912 7) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions and test structural fill for compaction. 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 fine-grained soils and at least 45 pcf for backfill consisting of imported granular materials. Cantilevered retaining structures which are separate from the structure 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 50 pcf for backfill consisting of the on-site fine-grained soils and at least 40 pcf for backfill consisting of imported granular materials. 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 95% of the maximum standard Proctor density at a moisture content near optimum. Backfill 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 Job No. 114 516A e tech -7 - 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 0.50 on the granular site soils or properly compacted structural fill. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 400 pcf for imported granular material. 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 with some risk of movement if the shallow, garage sub -slab soils become wetted. If the risk of movement is not acceptable, over -excavation of the upper clay soils to a depth of 3 feet below the floor slab and placement of properly compacted structural fill is recommended. The structural fill will serve to reduce but not eliminate the potential for movement if the under -slab soils become wetted. The structural fill should be placed in maximum 8 inch loose lifts and compacted to at least 95 percent of the standard Proctor value at a moisture content near optimum. 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 - Job No. 114 516A Gtech 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 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 I% to a suitable gravity outlet or drywell based in the gravel soils. 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 1 %2 feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the structure has been completed: Job No. 114 516A Hph 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 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 and foundation areas. 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 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 Job No. 114 516A CACPtech -10 - 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. James A. Parker, P.E., P.G Reviewed by: Daniel E. Hardin, P.E. JAP/ksw 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. 114 516A --- C-teCh APPROXIMATE SCALE 1"=20' GOLDEN BEAR i BORING 2 1 LOT FW 7 • LOT FW 5 LOT FW 6 BORING 1 I • 1 I 2nd FAIRWAY Owl*114 516A H edh 1 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 1 HEPWORTH-PAWLAK GEOTECHNICAL BORING 1 BORING 2 ELEV. = 100' ELEV.= 101' 0 0 13/12 WC=10.5 WC=10.6 13/12 DD=98 DD=102 -200=92 5 9/12 5/12 5 WC=10.0 WC=14.7 DD=94 DD=80 L -200=90 LL o CL Q 0 10 0 =' 25/4 30/6 10 0 15 15 Note: Explanation of symbols is shown on Figure 3. H 114 516A C� LOGS OF EXPLORATORY BORINGS FIGURE 2 HEPWORTH•PAWLAK GEOTECHNICAL LEGEND: TOPSOIL; sandy clay, some roots, slightly moist, light brown. CLAY (CL); silty, slightly sandy, medium stiff to stiff, slightly moist to moist, brown. GRAVEL AND COBBLES (GM); silty, sandy, dense to very dense, slightly moist, brown. M Relatively undisturbed drive sample; 2 -inch I.D. California liner sample. Drive sample; standard penetration test (SPT), 1 3/8 inch 1. D. split spoon sample, ASTM D-1586. 9/12 Drive sample blow count; indicates that 9 blows of a 140 pound hammer falling 30 inches were required to drive the California or SPT sampler 12 inches. TPractical drilling refusal. NOTES: 1. Exploratory borings were drilled on November 20, 2014 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 measured by hand level and refer to Boring 1 as 1 00'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 transitions may be gradual. 6. No free water was encountered in the borings at the time of drilling. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: WC = Water Content (%) DD = Dry Density (pcf) -200 = Percent passing No. 200 sieve 114 516A LEGEND AND NOTES I FIGURE 3 Moisture Content = 10.6 percent Dry Density = 102 pcf Sample of: Slightly Sandy Silty Clay From: Boring 1 at 2 Feet 1 0 0 TFO z 1 O C/)z a 2 x w z 3 O U) Cn w a 4 m O U Expansion upon wetti g 5 0.1 1.0 APPLIED PRESSURE (ksf ) 10 100 114 516A H G�"tecdh SWELL -CONSOLIDATION TEST RESULTS FIGURE 4 -HEPWORTH-PAWLAK GEOTECHNICAL Moisture Content = 14.7 percent Dry Density = 80 pcf Sample of: Silty Clay From: Boring 2 at 5 Feet 0 2 Compression o upon z 4 O wetting U) U) � 6 q- 0 O U 8 10 12 14 16 18 20 22 0.1 1.0 APPLIED PRESSURE (ksf ) 10 100 114 516A G490'rtech SWELL -CONSOLIDATION TEST RESULTS FIGURE 5 HEPWORTH-PAWLAK GEOTECHNICAL Q co 0 z 0 n cd c� cd U U U W CL O >> N s Vi C/i v1 � En ry) rA V) w ZN� OwJu a IL M z0y mU . U � QO o J Jz IL W w LU v - J Q J C.) U) N > UJ Z U) CL IL0 z a O V) a 0 J CD W J y p 001\0� 00 �Z Z Z W w7W O �ajz<00 O O O d O W N N Q c U O J w 0. 0 z Q r .-a N N 0