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HomeMy WebLinkAboutSubsoil StudyGeSF-1 tech HEPWORTH - PAWLAK GEOTECHNICAL Hepworch-Paivlak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970-945-7988 Fax: 970.945.8454 email: hpgeo@hpgeorech.com SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 8, SUN MEADOW ESTATES 0530 NORTH MEADOW DRIVE GARFIELD COUNTY, COLORADO JOB NO. 105 363 OCTOBER 19, 2006 PREPARED FOR: CARIBOU CONSTRUCTION ATTN: FRED COOKE 734 MAIN STREET SILT, COLORADO 81652 Parker 303.841.7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS -2 - FIELD EXPLORATION -2 - SUBSURFACE CONDITIONS -2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FLOOR SLA13S - 4 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 5 - PROFILE BORING - 6 - LIMITATIONS - 6 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2- LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4- SWELL -CONSOLIDATION TEST RESULTS TABLE 1 - SUMMARY OF LABOROATRY 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 8, Sun Meadow Estates, 0530 North Meadow Drive, 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 Caribou Construction dated May 3, 2005. Hepworth-Pawlak Geotechnical Inc., previously performed a preliminary geotechnical study for Sun Meadow Estates (formerly Manures View) and presented our findings in a report, dated March 28, 2000, Job No. 100 169. A field exploration program consisting of one exploratory boring in the building area and one profile boring in the septic disposal area was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the Iaboratory 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 above a full basement with 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 2 to 9 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. 105 363 C.tch -2 - SITE CONDITIONS Lot 8 is located on the west side of North Meadow Drive and was vacant at the time of our field visit. The building area is located in the central eastern part of the lot. Vegetation consists of grass and weeds. The ground surface in the building area is relatively flat with a gentle slope down to the southwest at a grade of about 3 to 4 percent. An irrigation ditch is located along the western property line and below the building area. FIELD EXPLORATION The field exploration for the project was conducted on October 10, 2006. One exploratory boring was drilled in the building area and a profile boring was drilled in the septic disposal area 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 track -mounted CME -45 drill rig. The borings were logged by a representative of Hepworth-Pawlak Geotechnical, Inc. Samples of the subsoils were taken with a 2 inch I.D_ spoon sampler. The sampler was 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 at Boring 1, below about Y2 foot of topsoil, consist of sandy to very sandy clay down to the depth explored of 25 feet. Laboratory testing performed on samples obtained from Boring 1 included natural moisture content and density, finer than sand size gradation and Atterberg limits. Results of swell -consolidation testing performed on relatively undisturbed drive samples of the Job No. 105 363 -3 - clay soils, presented on Figure 4, indicate low compressibility under conditions of light loading and existing moisture conditions with a low to high swell potential when wetted. 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 The clay soils are expansive when wetted and could heave lightly loaded footings and slabs -on -grade. The settlement/heave potential should be further evaluated at the time of construction. Considering the subsurface conditions encountered in the exploratory borings, the nature of the proposed construction and the soils typical of the area, the building can be designed with spread footings bearing on the natural soils. If the soils exposed at bearing level are expansive, subexcavation and placement with non -expansive structural fill or designing the footings for a minimum dead load could be needed. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural soils with low to no expansion potential should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. There could be some additional differential movement if the bearing soils become wetted. 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. PIacement of foundations at least 36 inches below exterior grade is typically used in this area_ Job No. 105 363 -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 a lateral earth pressure corresponding to an equivalent fluid unit weight of at least 55 pef. 5) The topsoil and any loose or disturbed soils should be removed and the footing bearing Ievel extended down to the undisturbed natural soils. The exposed soils should be evaluated for expansion potential. If they show moderate to high expansion potential, at Ieast 3 feet of non -expansive structural fill, such as road base, compacted to at least 95% of standard Proctor density should be provided below footing areas, 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural clay soils are expansive and there could be some heave of slabs -on -grade. Non -expansive structural fill could be needed below slabs to help reduce the heave potential. 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. AlI 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 granular soils devoid of vegetation and topsoil. Job No. 105 363 Gh -5 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. Where drains are installed, they 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, dry well or sump and pump. 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% feet deep. 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 Iandscape 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 lob No. 105 363 -6 - 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. 5) Landscaping which requires regular heavy irrigation should be located at Ieast 5 feet from foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by irrigation. PROFILE BORING A profile boring was drilled in the proposed septic disposal area at the location shown on Figure 1. The subsoils encountered, below about 1/2 foot of topsoil, consisted of sandy clay to 10 feet overlying clayey sand to the bottom hole depth of 15 feet. The log of the profile boring is shown on Figure 2. The sand layer is apparently not continuous through the building area. No free water was observed in the boring at the time of drilling and the subsoils were slightly moist. 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. I05 363 G .. :ech -7 - 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: Steven L. Pawlak, P.E. LEE/vad Job No. 105 363mech 5220 5220 LOT 9 1 1 1 11 APPROXIMATE SCALE 1' = 50' / LOT 8 105 0363 HvpwowrHPAwwcGEor cMracm. LOCATION OF EXPLORATORY BORINGS Figure t a) 10 15 20 25 LOT 8 BORING 1 ELEV. = 5225' PJ60/12 WC=6.4 DD=113 / i 60/5 WC= 7.5 / DD= 122 -200=75 LL -=28 / PI= 16 n 60/5 / 27/12 WC=7.4 DD= 121 -200=51 LL=22 PI=9 ✓ -� 50/12 i LOT 8 PROFILE BORING ELEV. = 5223' r / r r 35/6,35/3 1 r r / r1 30/6,35/5 t 40/6,20/2 f_• I Note: Explanation of symbols is shown on Figure 3. 0 5 10 15 20 25 105 363 Gam'► HEPwORM-PAWLAK GEOTECHNICAL LOGS OF EXPLORATORY BORINGS Figure 2 LEGEND: -7 TOPSOIL; organic sandy silt and clay, firm, moist, brown. CLAY (CL); sandy to very sandy, very stiff, siighlly moist, brown, low plasticity. SAND (SC); clayey, slightly gravelly, medium dense, slightly moist, light brown. Relatively undisturbed drive sample; 2 -inch I.D. California liner sample. 60/12 Drive sample blow count; indicates that 60 blows of a 140 pound hammer falling 30 inches were required to drive the California sampler 12 inches. NOTES: 1. Exploratory borings were drilled on October 10, 2006 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 (pcf) -200 = Percent passing No. 200 sieve LL = Liquid Limit (%) PI = Plasticity Index (%) 105 363 HD'WORT Gr.orrecitNicAL LEGEND AND NOTES Figure 3 Compression - Expansion % Compression - Expansion % 1 0 1 2 3 5 4 3 2 1 0 1 0.1 Moisture Content = 6.4 percent Dry Density = '113 pcf Sample of: Sandy Clay From: Boring 1 at 4 Feet, Lot 8 Expansion upon wetting 1.0 0 APPLIED PRESSURE -ksf Moisture Content = 7.5 percent Dry Density = 122 pcf Sample of: Sandy Clay From: Boring 1 at 9 Feet, Lot 8 1 Expansion upon wetting 0.1 105 0363 1.0 0 APPLIED PRESSURE - ksf HEPWO fl}'AWWC GEOTF-CHNJCAL 100 100 SWELL -CONSOLIDATION TEST RESULTS Figure 4 0 HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Job No. 105 0363 SAMPLE LOCATION NATURAL NATURAL DRY DENSITY(%) _(Pcf) GRADATION PERCENT ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (PSO SOIL OR BEDROCK TYPE BORING DEPTH (ft) MOISTURE CONTENT Com) GRAVEL SAND (%)NO. PASSING 200 SIEVE LIQUID LIMIT (%) PLASTIC INDEX (%) 1 4 6.4 113 Sandy CIay 9 7.5 122 75 28 16 Sandy Clay 14 7.4 121 51 22 9 Very Sandy Clay ,