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Home My WebLink AboutSoils Report 12.31.20131Itj 1111( rv1,1 (II.It•'Ilnu.'11,I1i, (Ilt il-�-••1'1111i 111'•l.i.It 1 I-1EPWORTH-PAWLAK GEOTECHNICAL 1 December 31, 2013 Pat Stucker 16040 Quarry Hill Drive Parker, Colorado 80134 palestUck erandco.coin ,i,int Job No.113 429A Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 16, Cerise Ranch, Larkspur Drive, Garfield County, Colorado Dear Pat: As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study for design of foundations at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to you dated November 7, 2013. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. We recently provided interim findings for this report in a letter dated November 22, 2013. We previously conducted a subsoil study for design of foundations at the site and presented our findings in a report dated April 29, 2005, Job No. 105 308. Proposed Construction: The proposed residence will be a 1 and 2 story wood frame structure over a walkout basement located on the site in the area of the exploratory pits as shown on Figure 1. Basement and garage floors will be slab -on -grade. Cut depths are expected to range between about 3 to 5 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. If building conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: The lot is vacant and unchanged since our previous report. The lots to the east and west have been developed with single family homes. The PVC pipe in Boring 1 was still in place with a water level of 14.7 feet below the ground surface. 4 l I p Ia 9� a (_1,�� `thi' �.. 1 -1 119 (.��, 11I,I� ,, ti , in�, 7 i)-li3 3-7y(�,, Si 1��.:}Ci5- -2- Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about 1 % feet of topsoil, consist of sandy silty clay. The upper 4 to 6 feet was medium stiff, slightly moist and light brown. Below about 5 to 8 feet, the clay became soft, very moist and dark brown down to the bottom of the pits, 8 %2 to 10 feet. Results of swell -consolidation testing performed on relatively undisturbed samples of sandy silty clay, presented on Figures 3 to 5, indicate the shallow clays down to about 6 feet have low compressibility under existing moisture conditions and light loading and a low collapse potential (settlement under constant load) when wetted. The deeper clays were moderately to highly compressible under loading. No free water was observed in the pits at the time of excavation and the soils were slightly moist to very moist with depth. The water level in Boring 1 was 14.7 feet below the ground surface when measured on November 3, 2013. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the previous borings and the nature of the proposed construction, we recommend spread footings placed on the upper, undisturbed natural soil designed for an allowable soil bearing pressure of 1,200 psf for support of the proposed residence. The foundation excavations should be kept shallow, within 5 feet of the existing ground surface. The clay soils at the site are compressible under light loading and a deep foundation such as piling extended down to the silty sandy gravel subsoils (encountered at 19 to 24 feet deep in the previous borings) could be used to provide a relatively high bearing capacity and a low settlement risk. Deep foundation recommendations can be provided if requested.. Due to the wet and soft soil conditions with depth, a full basement level is not recommended. Crawlspaces should be well vented to prevent developing high humidity conditions. Fill depth should belimited to about 4 feet above existing ground surface due to the soft subsoil conditions. Settlements under initial loading are expected to be about 1 inch. The soils tend to compress after wetting and there could be additional post -construction foundation settlement. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. The topsoil and loose and disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be reinforced top and Job No.113 429A -3- bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 55 pef for the on -site clay soil as backfill. 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 interior slabs to facilitate drainage and for capillary moisture rise. This material should consist of minus 2 inch aggregate with less than 50% passing 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 clay soils or a suitable imported gravel devoid of vegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered at shallow depths during our exploration, it has been our experience in mountainous areas 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 shallow 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 a suitable gravity outlet 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 %2 feet deep. Job No.113 429A -4- 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. Free -draining wall backfill should be capped with about 2 feet of the on -site, finer graded soils to reduce surface water infiltration. 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 pavement and walkway areas. 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 the building. 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 pits excavated at the locations indicated on Figure 1 and to the depths shown on Figure 2, the proposed type of construction, and our previous 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 pits 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 at once so re-evaluation of the recommendations may be made. Job No.113 429A Reviewed by: Steven L. Pawlak, P.E. DEH/ksw -5 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. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, HEPWORTH - PAWLAK GEOTECHNICAL, INC. Daniel E. Hardin, P.E. 2 •4% //f g// ie. .?Go aaaN0.16c5 iffiT /Oy N��NAL�� attachments Figure 1 — Location of Exploratory Pits Figure 2 — Logs of Exploratory Pits Figures 3 to 5 — Swell -Consolidation Test Results Table 1— Summary of Laboratory Test Results Job No.113 429A Gertech IRRIGATION DITCH LARKSPUR DRIVE �_▪ � • ��PT2 •\\ \ • - I f 6370 / BORING 1 \ \ \ LOT 16 \\ �\ 6370 • BORING FOR PREVIOUS • \ N ` \ STUDY, JOB NO. 6368 105308, DATED PIT 1N \ N 6366 APRIL 29, 2005 ■ • • \ BORING 2 LOT 15 APPROXIMATE SCALE 1"=60' BUILDING ENVELOPE IRR3GAi1CN DITC 6360 LEGEND • PIT FOR CURRENT STUDY LOT 17 6354 6362 6360 113 429A H'EPWORTH•PAWEAK GEDTECHN]CAL LOCATION OF EXPLORATORY PITS Figure 1 0 10 LEGEND: ./ PIT 1 ELEV.= 63' WC=19.3 DD=92 -200=87 WC=23.3 DD=104 PIT 2 ELEV.= 66' WC=9.1 DD=96 WC=11.5 DD=107 -200=86 TOPSOIL; organic sandy silty clay, with roots, medium stiff, moist , brown CLAY (CL); silty, sandy, medium stiff, slightly moist and light brown to soft, very moist and dark brown with depth. 2" Diameter hand driven liner sample. 0 5 10 NOTES: 1. Exploratory pits were excavated on November 7, 2013 with a Bobcat E50 mini -excavator. 2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory pits were obtained by interpolation between contours shown on the site plan provided. 4. The exploratory pit locations and elevations should be considered accurate only to the degree implied by the method used. 5. The Tines between materials shown on the exploratory pit logs represent the approximate boundaries between material types and transitions may be gradual. 6. No free water was encountered in the pits at the time of excavating. 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 Q. a) a 113 429A H HEPWORTf7•PAWLAK GnoTmCHNJCAI. LOGS OF EXPLORATORY PITS Figure 2 Compression % 0 1 2 3 4 5 6 7 8 9 Moisture Content = 19.3 percent Dry Density = 92 pcf Sample of: Sandy Silty Clay From: Pit 1 at 4 Feet — L Compression upon wetting 0.1 1,0 113 429A H HEPWOFi714•PAWLAK GEOTECHNICAL APPLIED PRESSURE - ksf 10 100 SWELL -CONSOLIDATION TEST RESULTS Figure 3 Compression % Compression % 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 Moisture Content = 23.3 percent Dry Density = 104 pcf Sample of: Sandy Silty Clay From: Pit 1 at 8 Feet No movement r upon wetting 0.1 .0 10 APPLIED PRESSURE - ksf 100 Moisture Content •= 9.1 percent Dry Density — 96 pcf Sample of: Sandy Silty Clay From: Pit 2 at 2 Feet El ! �. ---. Compression upon wetting 0.1 113 429A H 1.0 10 APPLIED PRESSURE - ksf HEPWORTH-PAWLAH GEOTC•CHNICAL SWELL -CONSOLIDATION TEST RESULTS 100 Figure 4 Compression % 0 1 2 3 4 Moisture Content = 11.5 percent Dry Density — 107 pcf Sample of: Sandy Silty Clay From: Pit 2 at 5 Feet Compression upon wetting 1 0.1 1.0 10 100 APPLIED PRESSURE - ksf 113 429A G'7 Stec 1 H EP WORTH PAWLAK GEOTEC! NEC AL SWELL -CONSOLIDATION TEST RESULTS Figure 5 HEPWORTH-PAWLAK GEOTECHNICAL, INC. TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Job No. 113 429A SAMPLE LOCATION PIT DEPTH (ft) NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITY GRADATION GRAVEL SAND (%) (%) PERCENT PASSING NO. 200SIEVE ATTERBERG LIMITS LIQUID LIMIT (%) PLASTIC INDEX (%1 UNCONFINED COMPRESSIVE STRENGTH (PSF) SOIL OR BEDROCK TYPE 1 4 8 19.3 23.3 92 104 87 2 2 Sandy Silty Clay Sandy Silty Clay 9.1 96 5 11.5 107 86 Sandy Silty Clay Sandy Silty Clay