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HomeMy WebLinkAboutSoils Report 01.16.2007JAN -18-2007 16:10 From:HP-GEOTECH 9709458454 Gtech HEPWORTH - PAWLAK GEOTECHNICAL_ To:9708760447 P.2'17 IIchu,i1 Lr 1, ( .'re tLLt.11,In 50't) (.t unt\ It ,:ul 144 l-ilCl•1tllnps,l Jlttt:it.tilt\'] rhorc V70 945.79titi I,a\ ');) c'45 N454 e m.td I r._;ocaL'liJ oN Irlh .t°in SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 15, BLOCK 7, THE RESERVE AT BATTLEMENT CREEK VILLAGE 0410 MEADOW CREEK DRIVE BATTLEMENT MESA, COLORADO JOB NO. 106 1042 JANUARY 16, 2007 PREPARED FOR: SANCHEZ DRYWALL, INC. ATTN: CARLOS SANCIHEZ P.O. BOX 209 SILT, COLORADO 81652 ParkQr- 303-841.7119 0 Cttlt>ricl<t Sirltli;i 719-613-5562 0 tilverdlo e 970-468-1989 JRN-16-2007 16:10 From:HP-GEOTECH 9709456454 To:9706760447 P.3'17 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS 2 - HELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS •• 4 - FLOOR SLABS - - UNDERDRAIN SYSTEM - 6 - SURFACE DRAINAGE • •• • r . • - 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 ]EST RESULTS TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS JAN -18-2007 16:10 From:HP-GEOTECH 9709458454 To:8708760447 P.4'17 PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed residence to be located on Lot 15, .Block 7, The Reserve at Battlement Creek Village, 0410 Meadow Creek Drive, Battlement Mesa, Colorado. The project site is shown on Figure 1. The purpose oldie study was to develop recotnmendatio.ns for the foundation design. 'Ihe study was conducted in accordance with our agreement for geotechnical engineering services to Sanchez Drywall, .Inc. dated December 20, 2006. 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 a single story, wood frame structure over a partial basement level and crawlspace. The floors of the attached garage and basement will be slab -on -grade_ Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 8 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. 106 1042 Gtech JAN -18-2007 16:10 From:HP-GEOTECH 9709458454 To:9708760447 P.5/17. -2- SITE CONDITIONS The site was vacant and covered with up to 3 inches of snow at the time of our field exploration. The lot is located on a ten -ace above the Colorado River with a moderate to strong slope down to the north at grades of about 10%. There is about 6 feet of elevation difference across the building area. Vegetation mainly consists of oak brush, sagebrush, grass and weeds. FIELD EXPLORATION The field exploration for the project was conducted on January 3, 2007, Two exploratory borings were drilled at the locations shown on Figure I 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 Exploratoty'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 'A foot of topsoil overlying stiff to very stiff, slightly sandy to sandy silt with some silty sand zones and scattered gravel below about 15 feet, Relatively dense basalt fragments up to boulder size in a sandy silt matrix was Job No. 106 1042 �h JAN -18-2007 16:10 Fram:HP-CaEUTECH 9709458454 To:9708760447 P.6'17 _3 - encountered beneath the silt soils at depths of about 18 and 26 feet. Drilling in the basalt rock soils with auger equipment was difficult due to the size and hardness oldie rock and drilling refusal was encountered in the deposit in Boring 1 at a depth 0128 feet. Laboratory testing performed on samples obtained from the borings included natural moisture content, density and finer than sand size gradation analyses. Results of swell - consolidation testing performed on relatively t.lndisturbed drive samples of the silt soils, presented on Figures 4 and 5, generally indicate a low compressibility under existing moisture conditions and light loading low collapse potential (settlement under constant load) when wetted and moderate compressibility under additional loading after wetting. The laboratory testing is surnmarizcd in Table 1. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist to .moist. DESIGN RECOMM.ENDATIQNS FOUNDATIONS The silt soils are hydroconapressive and there is a risk of post construction settlement if the bearing soils of a shallow foundation are welted 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 subsoils with a settlement risk. A deep foundation such as drilled piers or helical piles that extend down to the basalt soils could be used to reduce potential settlement and building distress. We should be contacted if a deep foundation is proposed. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural subsoils should be designed for an allowable bearing pressure of 1,200 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed Job No. 106 1042 G leiStech JAN -18-8007 16:10 From:HP-CEOTECH 9709458454 To:9708760447 -4- P.7'17 in this section will be about 1 inch or less. Additional settlements of 1 to 2 inches could occur depending on the depth and extent or wetting of the bearing soils. 2) The footings should have a minimum width 01 20 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 l'or 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 wails 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. 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 50 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 fill 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 40 pcf for backfill consisting of the on-site soils. Job No. 106 1042 Gagtech J'IN-18-2007 16:11 From:HP-CEOTECH 9709458454 To:9708760447 P.8/17 -5- All foundation and retaining strictures 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 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. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 350 pef. 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 Toads should be compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. Job No. 106 1042 Gtech TAN -18-2007 15:11 From:HP-GEOTECH FLOOR SLABS 9709458454 To:9708760447 P.9'17 -6- The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab - on -grade construction. The silt soils are compressible when wetted which could result in some slab settlement and distress if the bearing soils become wet. Precautions should be taken to prevent 'wetting of the subgrade soils. 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 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 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 Job No, 106 1042 JAN -1B-2007 16:11 From:HP-GEOTECH 9709458454 To:9708760447 P.10.17 -7- grade and sloped at a minimum 1141 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 SO% 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. An impervious membrane such as 20 mil PVC should he placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at ail 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 capped with about 2 feet of the on- site fine-grained soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits oral' backfill. 5) Irrigation sprinkler treads and landscaping which requires regular heavy irrigation, such as sod, should he located at least 5 feet from foundation walls. LIIVIITATIONS 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 ,fob No. 106 1042G�cgtech JAN718-2007 16:11 From:HP-GEOTECH 9709459454 To:9708760447 P.11'17 -8- express or implied. The conclusions and recommendations submitted in this report arc 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 contarninants (MOBC) developing in the future. if the client is concerned about MOl3C, 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 ol'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 bill by a representative of the geotechnical engineer. Respectfully Submitted, HEPWORTH- PAWLAI GES. !7' wk NC. Ab iso . 7 b1 tag a7 ,' `91ONAL �a Jordy Z. Adamson, Jr., P Reviewed by: Steven L. Pawlak, P.E. JZA/ksw Job No. 106 1042 Gtech JAN --18-2007 16:12 hrom:HP-6EOTECH 9709458454 To:9708760447 P.12'17 LOT 14 110 APPROXIMATE SCALE 1"=30' MEADOW CREEK DRIVE 100 BORING 2 i PROPOSED RESIDENCE — — — BORING 1 • LOT 15 BLOCK 7 LOT 2 1 106 1042 HePWO m+-PnwUj GvO ECHHIC;6L LOCATION OF EXPLORATORY BORINGS Figure 1 ' JAN -18-2807 16:12 From:HP-GEOTECH 9709458454 To:9708750447 BORING 1 ELEV.= 109' BORING 2 ELEV.= 104' 110 110 105 105 18/12 WC=1.9 DD=10t -200=30 100 17/12 WC=3.7 00=100 95 40/12 90 22/12 // J 12/12 / WC=3.1 00=101 -200=89 / - 12/12 / 27/12 100 95 90 85 80/12 85 80 80 1061042 Note: Explanation of symbols is shown on Figure 3. HEPWORTH-PAWLJ,K GearliCHPICAL LOGS OF EXPLORATORY BORINGS Figure 2 JAN• -18-2007 16:12 From:HP-GEOTECH 9709458454 To:9708760447 P.14/17 LEGEND: F 18/12 T TOPSOIL; slightly clayey sandy silt, organics, roots, firm, moist, brown. SILT (ML): slightly sandy to sandy, silty sand zones, scattered gravel below about 15 feet, stiff to very stiff, slightly moist, light brown, slightly calcareous. BASALT GRAVEL AND COBBLES (GM); in a sandy silt matrix, probable boulders, dense, slightly moist, 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-1588. 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 drilling refusal. NOTES: 1. Exploratory borings were drilled on January 3, 2007 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. 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 (pct) --200 — Percent passing No. 200 sieve 106 1042 HZPWh37r1+PAWLAK GeonicHwicAL LEGEND AND NOTES Figure 3 JAW18-2007 16:12 From:HP-GEOTECH 0 1 2 Compression % 3 4 0 1 2 3 970945844 To:9708760447 0.1 1.0 10 APPLIED PRESSURE - ksf P.15't7 100 Moisture Content = 3.7 Dry Density = 100 Sample of: Sandy Silt From: Boring 1 at 10 Feet percent pcf No movement upon wetting 1 0.1 106 1042 .0 10 APPLIED PRESSURE - ksf HIpwonTH PAwLMi GKO712C/1/13C14, SWELL -CONSOLIDATION TEST RESULTS 100 Figure 4 Moisture Content = 1.9 percent Dry Density = 10I pct Sample of: Silty Sand From: Boring 1 at 5 Feet ' 1 -....—_,.....wetting `C �••-ra •� J, Compression upon 0.1 1.0 10 APPLIED PRESSURE - ksf P.15't7 100 Moisture Content = 3.7 Dry Density = 100 Sample of: Sandy Silt From: Boring 1 at 10 Feet percent pcf No movement upon wetting 1 0.1 106 1042 .0 10 APPLIED PRESSURE - ksf HIpwonTH PAwLMi GKO712C/1/13C14, SWELL -CONSOLIDATION TEST RESULTS 100 Figure 4 ,7RN••18-2007 16:12 From:HP-GEOTECH 9709458454 To:9708760447 P.16'17 Compression % 0 1 2 3 4 Moisture Content = 3.1 percent Dry Density = 101 pcf Sample of: Slightly Sandy Silt From: Boring 2 at 4 Feet Compression upon wetting } 0.1 1.0 APPLIED PRESSURE • ksf 10 100 106 1042 Hswwerm PAvn_Au GlkmmCHJ UCAL SWELL -CONSOLIDATION TEST RESULTS Figure 5 HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 SUMMARY OF LABORATORY TEST RESULTS BORING �.OrATFaN DEPTH NATURAL MOISTURE CONTENT NATURAL DRY DENSITY cRADAT1GN GRAVEL SAND PERCENT PASSING LIQUID NO. 200 LIQ SIEVE A'TFERBERG Limas uNCONFINED PLASTIC o ST INDEX Job No. 106 1042 SOIL OR BEDROCK TY?E ss 5 10 1.9 3.7 101 100 30 3.1 101 JAN -10-2037 1G:12 From:HF-GEOTECH bSb8SVGOL6 Lb12e9LBOL6:01