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Home My WebLink AboutSubsoil Study for Foundation Design 07.07.2006I I IPWORTH - PAW L-AK G í:.OTË:C t.il.l lCAl- i ir i'rt' lri i'tr l:rl. (ìr.rrigçi-,¡1¡,..,1, ¡,.,..'iil],-l t .,,,;rirr. l:i,,¡.1 I 5,.1 (.,1,:rrrt',u ', | ;iplirrgs, ( ì,irrllr,.i, i ¡ I r.rrlì f'l',(.irr :' /;r-'.'.1 ¿l 5 - 7\)Slì FäN:9'it)-'J+i-lì45+ cnrai [: lr¡..r:ct,(àhpgcorcci r.c, rr rr July 7,2006 Nick Anthony Builders Attn:Nick Ores 1429 West2grH Street Loveiand, Colorado 80538 Job No,106 0380 Subject:subsoil Study for Foundation Design, proposed Residence, Lot 37,Filing 6, Elk Springs Subdivision, Garfield County, Colorado Dear Mr. Ores: 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 April 18,2006. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. We provided interim findings in a letter datgd May 17,2006, Job No, 106 0380. Hepworth-Pawlak Geotechirical, Inc., previously performed a prelirninary geotechnical study for Filings 6 through 9, Elk Springs (formerly Los Amigos Ranch PUD) and reported our findings on February 14, 1997, Iob No, i97 617. Proposed Construction: Building plans for the proposed residence are conceptual and this report \ryas prepared for purchase of the property, Typical construction in the area consists of one or two stoty v/ood frarne structures above a basement, crawlspace or slab- on-grade floor with aü attached garage. The site is shown on Figure 1. Cut depths are expected to range betr¡,een about 2 to 8 feet. Foundation loadings for this type of construction are assumecl to be relatively light for the assumed type of construction, If building conditions or foundation ioadings are significantly different from those described above, we should be notified to re-evaluate the recotrunendafions presented iri this report, Site Conditions: The site is located at the southeast cornor of Woodruff Road and Woodruff Place. Vegetation consists of a pinion and juniper forest with a ground cover of grass, weeds and sage bnrsh. The ground surface is relatively flat in the building area with a slight slope down to the southwest. Scattered basalt cobbles and boulders are visible on the ground surface. Subsurface CondÍtions: Ihe subsurface conditions atthe site were evaluated b1' excarrating three expiclratory pits at the apilroximate locations shown on Figure 1. The lcrgs of the pits are presented on Figure 2. The subsoils e,ncountered, below abour one foot of topsoil. consist of nil to one foot of sandy clay over:lying basalt cobbles and bcri:lders in a silt and sand lnatrix. About 2 feet of gravelly silt and sand was obsen'ed in M Nsrv ô\v¡,fËF:- K*,B'lf{ åk5(?c${ffi '.) r,'t,.1 ì ,,':¡ '!' ...,i..,:..i,'lrr.,iiil. .,'.i. iìi ..,if": u' ¡ii.,.1.1¡'¡!¡¡.ìílri.: .rr' -,ji;ljl "i,,..,t .| Pit 3 below the topsoil and above the basalt cobhles and boulders, Results of swell- consolidation testing perfonned on a relatively un¿ir*rbed drive sample of the silt and sand matrix soils frorn Pit 1. presented on Figure 3, indicate low to morlerate compressibility under conditions of loading and wetting, Nt-r free v/ater was observed in the pits at the time of excavation and the soils were slightly moist to 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 natural basalt rock soil designed þgu¡lgpl"r:qtq_ql?rlQ_Q p:{for support of the proposed residence. inches for continuous walls and_2leSl fof_cqhryU. Utility trenches may require rock excavating techniques such as chipping or blasting for an le soil The upper fine- grained soils and matrix soils tend to compress after wetting and there could be some post-construotion foundation settlement. Footinss should bc a mmlmum 16 and deep cut areas , Loose and disturbed soils encountered at the foundation bearing levei within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. Voids created from boulder removal at footing grade should be filled with a structural material such as road base compacted to 95 percent standard Procotor density at a moisture content near optimum, 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 wal1s shouid be reinforced top and bottom to span iocal anomalies such as by assuming an glgpÆgjglgl!-.g!-A!qaq!*] Zfç4. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressure based on an equivaient fluid unit \ /e1 ofat least 50 for the on-site soil as backfill, Floor Slabs: The natural on-site soils, exclusive of topsoii, are suitable to support lightly loaded slab-on-grade consfruction, To reduce the effects of some differential moveûient, floor slabs should columns with oints \a,hich allow unrestrained Floor slab control joints to reduce damage due to shríirkage cracking. The requirements for joint spacing and slab reinforcement should be established by the designer baseci on experience and the intended slab use. basement A minimum 4 inch la of free- This material should consist of minus 2 inch aggregate with less than 500/o passing the No. 4 sieve and less than?Yo passing the No. 200 sieve. Ali fill materials for support of floor siabs should be compacted to at least 95Yo 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 hearry precipitation or seasonal ruuoff. Frozen ground during spring runoff can create a perched condition.We recommend below-srade constructi on_retaìn in s .lob No,l06 0380 underdrain system. be tected from and such as céibtecfi walls,ace and basement up by ¿¡ pressure a-_1 - The drains should consist of drainpipe placed in the bottom of the wall b ackfill surrounded above the invert level with free-draining granular material. The drain should be laced at each level ofexcavation and at acent shedataFree-draining granular material used in the underdrain system should contain less than 2%passing the No. 200síeve, less than 50?'o passing the No, 4 sieve and have a maximum size of 2 inches. Thedrain gravel backfill should be 4t least lyz feet d.eep Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed:1) Inundation ofthe foundation excavations and underslab areas should be avoided during construction, Drying could increase the expansion potential of the soils, 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%o of the maximum standard. Proctor densi¡'in landscape areas, Free-d.raining wall backfill should be capped r'vith about 2 feet of the on-site, finer graded soils to reduce surface water i¡rfiltration, 3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directioor. W- recomrnend 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 ¿Ìreas. A sr¡'ale rnay be needed uphill to direct *urd"" runoff around the residence. 4) Roof don'nspouts and drains should discharge well beyond the limits of all backf,ill, 5) Landscaping u'hich requires regular hea,r1, irrigation and lawn sprinkler heads should be located at least 10 feet frorn the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils beloq,the foundation caused b), irrigation. Limitations: This study'has been conducted in accordance u,ith ge¡erail¡, as..ttra geotechnical engineenng pnnciples and practices in this arca atthís 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 excar¡ated at the locations inciicated on Figure I arrd to the depths shown on Figure Z, theproposed type of construction, and our experience in the area. Our services do not include deiermining the presence, prevention or possibility of rnold ol other biological contaminants (MOBC) developing in the future. If the ciient is concemed 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 excavatiori is perfonned. If conditions enccunteted during coustruction appear different from those described in this report, we should be notified at once so re-evaluation of the recommendations may be made. .lob No.l0ó 0380 Gäbtech -4 This report has been prepared for the exciusive use by our client for design purposes. We are not responsible for technical interpletations b), otirels of our infonnatiori, As the proiect evolves, we should provide continued consultation and field services during construction to revieu' and monitor the implementation of our recommenclations, and to verify that the recornmendations irave been appropriately interpreted. Sigfiificant design changes may require additional analysis or modifications to the recommendations presented herein. We recomnjend on-site observation of excavations and foundation bearing strata and testing of structural frll by a representative of the geotechnical engineer. If you have any questiotrs or if we nray be ullurther assistance, piease let us know Respectfuliy Submitted. HEPWORTH - PAWLAK GEOTECHNICAL, INC. ,,,.:"/ '''.i.l i-.'Louis E, Eiler Reviewerl hy Daniel E Hardin, P. LEE/vad attachments Figure I -oratory Pits Figure 2 - Logs of Exploratory Pits Figure 3 - Swell-Consolidation Test Results Job No. I 0ó 0380 cåFtectr APPROXIMATE SCI-AE '1 ": 60' LOT 38 1 PIT 1¡ LOT 37 FILING 6 I I LOT 36 Cr E LL LLlÍôoô 5 ¡ I Ptï E L PIT 3 E WOODFUFF PLACE 106 0380 tu HEPWoFÍH-PA$/LAR GEo'TEGHNICAL LOCATION OF EXPLORATORY PITS Ëigure 1 PIT 1 PIT 2 ñ W I PIT 3 0 WC=28.9 DD=81 0 ll) 0) LL Ic 0_oo LEGEND TOPSOIL; sandy silt and clay, organic, moist, dark brown, CI-AY (CL);sandy, medium stiff, moist, reddish brown. sAND AND slLT (SM-ML); gravelly, medium dense, slightly moist to moisi, light brown to white, calcareous. h-fr W ffifriJ:"ttj"-t"tt-lND BOULDERS (GM); in a silt and sand matrix, dense, slishty moist ro moist, righr brown 2" Diamctcr hand driven liner sanple, Practical digging refusal with backhoe NOTES: 1' Ëxploratory pits were excavated on May 10, 2006 with a cat 420D backhoe, ' båi?i3ï of exploratory pits were measured approximately by pacing from features shown orrthe stte pian 3' Elevations oi exploratory pits were not measured and the logs of exploratory pits are drawn to depth, 4' The expioratory pit iocations and elevations should be considered accurate only to the degree implied by the methodr-lsed. S The lines between materials shown on the exploratory pit logs represent the approximate boundaries beiweenmaterial types and transitions may be gradual, 6 No free water was encountered in the pits at the time of excavating. Fluctuatjon'in water level may occur with time.7, Laboratory Testing Results: WC = Water Content (%) DD = DV Density (pcfl þ 1 06 03u0 LOGS OF EXPLOFìATORY PITS Figure z 0 i,;II t'ltl I]il lii! iì.l ,;1I l '{ I l I j I Ij i i l I , 2 Õù òs co'ı Ø Eo E LJ Moisture Content = 2B,g Dry Density = B'1 Sample of: Silt and Sand Matrix From: Pit 1 at 2 Feet percent pcf lt S-* ilt\-il llttr il No'movement upon wetting I I I lt lt lt 1,0 10 APPLIED PRESSURE - ksf 1 06 0380 ffite*r.PÀwl..AK GE TTECHNICAL SWELL-CONSOLI DATION TEST RESLILTS Figure 3 0,1 100