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HomeMy WebLinkAboutSoils Report 11.29.2006Gtech HEPWOI7rH PAWLAK GEOTECHNICAL November 29, 2006 Muse Architects Attn: Dan Muse 46 Weant Boulevard Carbondale, Colorado 81623 I kprr.mis-Il 'I.L tJ . tkalyd, I„v 5..11P Guu+r ftw.l 154 ra r$I I't • me: 47 t'19 5.795.9 Fax: 970.45.5454 0,404: l,a+rr rbm.. 1 dh.c.,sn Job No.106 0943 Subject: Subsoil Study for foundation Design and Percolation Test, Proposed Hewitt Guest House and Detached Garage, Lot 7, Roaring Fork Preserve, Garfield County, Colorado. Dear Mr. Muse: As requested, Hepworth-Puwlak Geotechnical, Inc. performed a subsoil study and percolation test for foundation and septic disposal designs al the subject site. The study was conducted in accordance with our agreement for geoleclmical engineering services to Muse Architects dated November 1, 2006. Thc data obtained and our recommendations based on the proposed construction and subsurface conditions encountered arc presented in this report. I-lepworth-Pawlak Geotechnical, Inc. previously conducted a preliminary geotechnical study for the development and presented our findings in a report dated November 30, 2000, Job No. 100 627. Proposed Construction: The proposed guest house and detached garage will he single story wood frame structures located on the site as shown on Figure 1. Ground floors will be structural over a crawlspacc for the guest house and stub -un -grade in the garage. Cut depths arc expected to be about 3 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction Thc septic disposal system is proposed to be located southwest of the structures. 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 site was vacant at the time of our field exploration. There are shallow irrigation ditches across the site. Two deeper irrigation ditches are located to the north of the guest house. The ground surface is relatively flat with a gentle slope down to the northwest. Vegetation consists of grass and weeds with cottonwood trees along the larger ditches. The area of standing water shown on the site plan was not observed at the time of our site visit on November 20, 2006. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits in the building area and one profile pit in the septic disposal arca at the approximate locations shown on Figure 1. Thc logs of the pits arc presented on Figure 2. The subsoils encountered, below about 1 to 1% feet of topsoil, Parker 303.841-7119 • Colorado Svnnes 719633.5562 • Silverthnme 970 46S 19.9 -2- generally consist of relatively dense, slightly silty sandy gravel with cobbles and small boulders About 1'h feet of medium dense, silty to very silty sand was encountered between the topsoil and gravels in Pit 2. Results of swell-consolidation testing perforated on a relatively undisturbed-sample of the silt and sand soils, presented on Figure 3, indicate law compressibility under existing moisture conditions and light loading and a low to moderate collapse potential (settlement under constant load) when wetted. The sample showed high compressibility upon increased loading after welting. Results ofa gradation analysis performed on a sample of the gravels (minus 5 inch fraction) obtained from the site are presented on Figure 4. The laboratory test results are summarized in Table I. No free water was observed in the pits at the time of excavation and the soils were slightly moist to moist. A pit excavated on Lot 7 as part of the preliminary study encountered similar soils to the excavated depth of 6 feet and groundwater at a depth of 5'h feet in August 2000. Foundation Bearing Conditions: Construction of the guest house and garage at the site should be feasible based on geotechnical considerations. The natural gravel alluvium sail possesses moderate bearing capacity with a low risk of settlement and should be adequate for support of the proposed building foundation. Groundwater was observed in a pit excavated on lot as part of the preliminary study at a depth of 5% feet below the existing ground surface. it has been our experience in the arca that groundwater levels can rise during periods of seasonal runoff and heavy precipitation. Due to the relatively shallow groundwater conditions encountered in the area, crawlspace areas should be relatively shallow and kept well ventilated. As an alternative, a slab-on-grade floor could be considered to reduce the risk of having a wet crawlspacc. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on the undisturbed natural gravel sell designed for an allowable soil aringpressure of 3,000 psf for support of the proposed guest house aniThe upper silt and sand soils tend to compress aper wetting and there could be some post- construction foundation settlement Footings should be a minimum width of 16 inches for continuous walls and 2 feet for courns. ihy scan and%ase disturbed soils encounicterai theoun4ition'�Can igeve within the excavation should be removed and the footing bearing level extended down to the undisturbed natural gravel soils. Voids created by the removal of large rocks should be backfilled with compacted sand and gravel or with concrete. 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 bottom to span local anomalies such as by assuming an unsupported length of at least 10 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 45 pcf for the on-site soil, excluding vegetation, topsoil or oversized rock, as backfill. Job No.1%0443 -3 - Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support Tightly loaded slab -on -grade construction. To reduce the effects of some differential movement, fluor 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 t slab use. A layer oP i-iin h screen rock couldsexperience be placed below sllabson-grade as o tended leveling course. 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 gravel soils devoid of vegetation, topsoil and oversized rock. Surface Drainage: The following drainage precautions should be observed during ngs have been construction and maintadation of ilia foundation excavationed at all times after the ns and underslab areacompleted: 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 pavement and walkway areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. Percolation Testing: Percolation tests were conducted on November 21.2006 to evaluate the feasibility of an infiltration septic disposal system at the site. One profile pit and three percolation holes were dug at the locations shown on Figure 1. The test holes (nominal 12 inch diameter by 12 inch deep) were hand dug at the bottom of shallow backhoe pits and were soaked with water one day prior to testing. The soils exposed in the percolation holes are similar to those exposed in tate Profile Pit shown on Figure 2 and consist of about 1'A fat of topsoil overlying slightly silty sandy gravel with cobbles and small boulders to the pit depth of It feet. The percolation test results are presented in Table 2. The percolation test results indicate infiltration rales between 3 and 5 minutes per inch with an average of 4 minutes per inch. Based on the subsurface conditions encountered and the percolation test results, we recommend that a professional engineer be engaged to design the infiltration septic disposal system, 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 rather expressed 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, the proposed type of construction and our experience in 10b No.I06 0943 GaSteat, -4 - 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. 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 hove 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 Id us know. RespectfullySubmitted, HEPWORTH - PAWLAK G Daniel E. Hardin, P E. .12.A/low attachments Pigmy 1 - Location of Exploratory Pits and Percolation fest Holes Figure 2 - Logs of Exploratory Pits Figure 3 Swell -Consolidation Test Results Figure 4 - Gradation Test Results Table i - Summary of Laboratory Test Results Table 2 - Percolation Test Results cc Ernest Kollar Engineers, inc. - Ann! Emit Kollar lob No.106 09 1 sti LOT 9. PAIN Orr OF STANDING WATER TIME OF SURVEY 4 1 :1 Gtech LOCATION OF EXPLORATORY PITS AND f FIGURE 1 106 0943 1 PERCOLATION TEST HOLES P11 EL.EV -• 995' __0 MT 2 ELEV9419' WC•52 00-93 -MP- 50 PR0FIME IMT ELEV.- 1001' -1 +4-7s -J -200-2 0 _ 5 10_.— — - 10 LEGEND: ® TOPSOIL: sandy silt end day. organic, roots. km. malst. dark brown. SAND (Ski), silty to very silty, medium dense. sMghty moist. ROM brown - GRAVEL AND rwrn. GRAVELAND COBBLES (GP -GM). sandy. slightly oily. with smolt boulders, dense. moist. ROM brawn, wbrounded to rounded rocks. ? Diameter trend drivel liner sernphe. Disturbed bulk sample. NOTES: 1. Ehpbratory pits were excavated on November 20 2000 with a Ya neer htinkercavalar. 2. Locations of exploratory PIs were mewed appnnr1etely by padng Iron lealuras stow, an the situ plan provided. 9. Elevations el exploratory pits were obtained by interpolation between contours shown on the site plan provided. Logs are drawn lo depth. 4. The exploratory pl locations and elevations should be considered eccsale only to the degree tr pled by the method used. rs The tines between melerids shown on the exploratory pit bps represent the approximate boundaries between mated types end handbells may be gradual. 0. No tee water was encountered i, the pits at the time al excavating. Fluctuation i, water level may ocarwith throe. 7. Laboratory Testing Hese WC : Water Content (%) DDA Dry Density (pd) +4 d Permit retained on the No. 4 slave .200 - Percent passing No. 200 sieve 146 0943 LOGS OF EXPLORATORY PITS !Figure 2 0 at 2 3 7 5 6 7 8 0 1D 11 12 0-1 Moisture Content a 5.2 Pew Dry Dena1ty 93 Pd Sample 01: Sill and Sand From: Pit 2 al ?Xs Feat Compression Wan walling f 1.0 10 a00 MPl1ED PiamainE - Imt 10609A3 tech 1 SWELL-CONSOLUDA71ON TEST RESULTS 1 Figure 3 rw.m.n+rwuwAkarmm.oseu 11v011D►tlumpalo&S [ so:bur/gyms it `11� 77 �90�1 us 57101 NU 6734[3 CLEAR SOUORE morons0 L` MMt181AN. R116MK4YH. 114161. 0200 M06 MD PW 116 P6 44 31V W 1 172 a 176' 0. 160 10 20 30 > == J=_ --=.=—=_=_�====— 70 m 70 30 .000 1 10 3:14 4.70 45 09 ]7.5 7112 1152 27 200 .001 .2 � ma 31W 919 l37 914 ,150 ,500129 0140E'EA OF PAn11 01.5 N ►16ui1E77it4 my.,1 1Ye 1 SRA GRAVEL 711 % NOM DONT % SAMPLE OF Sandy Gravel with Cobbles SAND 22 % SILT AND MAY 2 % PIAST1C11Y INDEX % FROM: Pi13 al 4 Feel 70 10 106 0943 GRADATION TEST RESULTS I Figura 4 Job No. 105 0943