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Home My WebLink AboutSubsoil Study for Foundation Design 03.31.2003t March 31, 2003 Rapids Development Corporation Attn: Gene Hilton 2102 West Arapahoe Drive Littleton, Colorado 80120-3008 Hepworth-Pawlalc. Oeotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970-945-7988 Fax: 970-945-8454 email: hpgeo@hpgeotech.com Job No. 103 198 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 10, The Rapids on the Colorado, County Road 335, Garfield County, Colorado. Dear Mr. Hilton: As requested, Hepworth-Pawlak Geote~hnical, 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 Rapids Development Corporation dated March 5, 2003. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Hepworth-Pawlak Geotechnical, Inc. previously conducted percolation testing for the subdivision development and presented our findings in reports dated May 12, 1995 and August 8, 1996, Job No. 195 217. Proposed Construction: The proposed residence will be a one or two story wood frame struclUre located in the area of ~he pits shown on Figure 1. Ground floor will be either structural over a crawlspace or slab-on-grade. Cut depths are expected to range between about 3 to 4 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 site was vacant at the time of our field exploration. The ground surface in the building envelope has been graded relatively flat with a gentle slope down to the northwest. There is about 2 feet of elevation difference across the building envelope. A steep fill slope had been constructed on the north-northwest side of building envelope. The Colorado River is located about 125 feet to the north-northwest and about 10 feet lower in elevation. Vegetation consists of sparse grass and weeds. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits with a backhoe at the approximate locations shown on Parker 303-841· 7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989 Rapids Development Corporation March 31, 2003 Page 2 - 2 - Figure I. The logs of the pits are presented on Figure 2. The subsoils encountered, below about Vi to 1 Yi feet of topsoil, consist of 3 feet of medium stiff silt and sand overlying relatively dense, slightly silty sandy gravel with cobbles and boulders to the pit depths of 4 to 4Y2 feet. Results of swell-consolidation testing performed on a relatively undisturbed sample of very silty sand, presented on Figure 3, indicate low compressibility under existing moisture conditions and light loading and a low collapse potential (settlement under constant load) when wetted. The sample showed moderate compressibility upon increased loading after wetting. The laboratory test results are summarized in Table 1. No free water was observed in the pits at the time of excavation and the soils were slightly moist. 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 naturaJ soils designed for an allowable soil bearing pressure of 1,000 psf for support of the proposed residence. The upper fine grained soils tend to compress after wetting and there could be some post-construction settlement if the bearing soils become wetted. Footings bearing entirely on the underlying dense gravels can be designed for an allowable soil bearing pressure of 3,000 psf. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. The topsoil and loose 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. 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 nnd 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 50 pcf for the on-site soil as backfill. Floor Slabs; The natural on-site soils, exclusive of topsoiJ, are suitable to support lightly loaded slab-on-grade construction. The upper fine grained soils are compressible when wetted under load. To reduce the effects of some differencial 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 sand and gravel, such as 3/4-inch road base, should be placed beneath slabs-on-grade for subgrade support. Job II 103198 Rapids Development Corporation March 31, 2003 Page 3 -3 - This material should consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and less than 12% 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. 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. 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 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 pits excavated at the locations indicated on Figure 1 and to the depths shown on Figure 2, the proposed type of construction, and our experience in the area. Our findings include interpolation and extrapolation of the subsurface condilions 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 Job# 103 198 Rapids Development Corporation March 31, 2003 Page 4 -4 - 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. Trevor L. Knell Reviewed by: TLK/ksw attachments Job# 103198 - COl.OHAOO HIVEH --___ -5490--------- ---i--549s---.,.........r---L.. I LOT 10 LOT 9 r ---.--. ' -------,.---. I - - -.Jt \ --~ I / r-: \ PIT 1 I I • I l I \ I \ BUILDING I - APPROXIMATE SCALE 1"=50' NOTE; CONTOUR LINES SHOVtN ARE PRIOR TO SITE GRADING FOR SUBDIVISION DEVELOPMENT -- LOT 11 ---.... ~ . ENIPE I L_____ _ ____ J PROPERTY ,,___ LINE • PIT 2 RAPIDS VIEW ROAD -- 103 198 HEPWORTH-PAWLAK GEOTECHNICAL, INC. LOCATION OF EXPLORATORY PITS Figure 1 .. ~ I :5 i c o· 5 10 LEGEND: PIT 1 F'JT 2 WC-7.3 DD-92 WC-5.5 -200-•1 DO-tO -2oo-1S TOPSOIL; silt and sand. scattered rock, organics, moist, dark brown. 0 5 10 SlLT ANO SAND (ML-SM): with cloy lenses/layers, stratified, medium stiff, slightly moist. light brown, trace colcoreoua. SANO (SM): 1llty, medium dense, slightly moist, brown. GRAVEL, COBBLES ANO BOULDERS (GP-GM); sandy, sllghtly stlty, dense, sllghtly moist, light brown, subrounded to rounded rock. 2• Diameter hand driven liner sample. NOTES: 1. Exploratory plts were excavated on Morch 21, 2003 with o backhoe. 2. Locatlons of e><ploratory pits were measured approxlmatety by toping from features shown on the site plan provided. 3. ElelfOtions of exploratory pits were not measured ond logs of exploratory pits ore drawn to depth. 4. The exploratory pit loc:otlons should be considered accurate only to the degree implied by the method uaed. 5. Tho lines 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 el<c<:1vating. Auctuai.ions in water level may occur with time. 7. Laboratory Testin9 Rewlts: WC .. Water Content ( " ) DD • Ory Density ( pcf ) -200 • Percent passing No. 200 sieve 103 198 HEPWORTH-PAWLAK GEOTECHNICAL, INC. LOGS OF EXPLORATORY PITS Figure 2 .. Ql i! :S i 0 --. . Moisture Content • 5.5 percent Or-y Oensfty = 90 pcf . -200 -15 percont Sc::imple of: Very Silty Sand From: Lot 10, Pit 2 at 3 Foet 0 -,., I>.- 1 ,_ I~ ... ~ t-. Compression M "'upon ~ 2 wetting 1ii ~ 1111 ~ CD ... a. § 3 ~~ (..) 4 5 0.1 1.0 10 100 APPLIED PRESSURE -ksf 103 198 HEPWORTH-PAWLAK SWELL CONSOUDA TION GEOTECHNICAL, INC. IEST RESULTS Figure 3 HEPWORTH-PAWLAK GEOTECHNICAL. INC. TABLE 1 JOB NO. -103 198 SUMMARY OF LABORATORY TEST RESULTS SAMPLE LOCATION NATURAL NATURAL GRAO"TION PERCENT ATTERBERG LIMITS UNCONFINEO Pll llEP'l'H MOISTURE D~Y GAAVE\. SANO PASSING UQUID Pl.ASTIC COMPRESSNE so.LOR jlHt) CONtENT OEHSITV 1'%1 1'1111 N0.2llO LIMIT INDEX STREHGTH EIEOROCK TYPE ('llol (pell SIEVE (%1 1%1 IPSFJ 1 2 }2 7.3 92 47 very silty sand 2 3 5.5 90 15 silty sand . . GRADING PIAN REQUIREMENTS: '· strip ond .tor;Jcp/I• topllQ// from bulldlng footprint, drfwway. ISDS, and B' ~ ~rMte around building "-fore construction bdg1°M. 2. Building Rni~ floor •ltwation to b• 55()2, fi:J or abo'ltl bond on SE Lot 10 ea,,,., elevation • COL ORA DO RIVER .J. The ground sul'foce surTDunding tM ext.rlor of th• building aho/J H lloP«J from th• foundation In all dlr«:tioM wltli a minimum al.-of s• In the Hn1t 10 fHt in un/XTfW area. and .3" in tM nrat 10 fHt for pavement and walkway or.a.. Roof down~ and drain• #JouJd dlaCharp "'' bdyond th• Umb of all bac/cl/1/. Lant#caplng which fW/UVN 1'9gular ll«Wy ltrlgatlon ahould b• located at /«lit 5 fHt from foundation Illa/la. DS 07/30/04 LE ,. -40' INlllt Chrltl Hale JU lot10Site 423 Residence Grading Plan & ISDS Site Plan Lot 1 O -Rapids on the Colorado Rapids Development Corporation '•. RAPIDS Vii jfRicHARD L. ROI.SAN Prpf•ulonal Land SutwJror LS. 1»01 477.3 214 Rd. L Silt Colorado ii (970) 876-2947 ..=Ji • MOUNT/\IN CROSS ENGINEERING, INC. Civil and Environmental Consulting and Design 8261/2 Grand Avenue Glenwood Springs, CO 81801 ph 97D.94S.5!144 I>< 970.945.SSH www.mount&lncroH-.com April 20, 2006 Mr. Andy Schwaller Garfield County Planning 108 81h Street, Suite 201 Glenwood Springs, CO 8160 I . MOUNT/\IN CROSS t:N<ilN!ERIN6, INC. CIVIL ANO ENVIRONMENTM CONSULTING AND DESIGN RE: Review of Lot 10 ISDS, Rapids on the Colorado Subdivision Dear Andy: The purpose of this memo is to confmn that on Thursday, April 20, 2006, Mountain Cross Engineering, Inc. inspected the ISDS for Lot I 0. In the professional opinion of Chris Hale, as a professional engineer licensed in the State of Colorado, #35964, and a representative of Mountain Cross Engineering, Inc, it appeared to be installed per the plans prepared by Mountain Cross Engineering, Inc. Feel free to call if any of the above needs clarification or if you have any questions or comments. !L__ C: Mr. Gene Hilton ·~ 826 1/2 Grand Avenue • Glenwood Springs, CO 81601 PH: 970.945.5544 • FAX: 970.945.5558 • www.mountaincross-eng.com