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Home My WebLink AboutObservation of Pit Excavations? le1+-a:*h-f:,.rl,rii *er.:*':iirri;:;i" i l:tiiliil ii:t;::: y- il,:;;ri i ;i.i {il': irrr*iid 5;-,r i*gr, Cyiar.r,l.i S I *l1 I f lx rn*: ?7il"1]-l'i,?rjji3 I.I EPWORru*FAWLAK G E{}THCHN ICAL t ;.c : .t; 7t1"9-l ii -l'i'i 5 4 **!::il: l'ri:+1r:*'9illilgdllf dll.r:i1!ri December 21,2015 Ryan Pratt P.O. Box 162? Carbondale, Colorado 81623 @ Job No. I 15 5754' Subjectt Observation of Pit Excavations, Proposed Residence, LotZ3, Fiting S, Elk Springs, 203 Wood Nymph Road, Garfield Counqr, Colorado Dear Ryan: As reguested, the undersigned representative of llepworth-Pawlak Geotechnicat,Inc. met with you and observed the shallow pil excavations at the subject sile on December 16, 2015 to evaluate the soils exposed for foundation support. The findings of our observations and recommendations for the foundation design arc presented in this reporl The services were performcd in accordance with ouragreement forprofessional cngineering services to you, dated Decemberg, 2015. Proposed Conslnrclion: The proposed rcsidence will be a two story wood frame struclureover a crawlspacc or the lower lOvel may be a shallow walkout basement level. The house will bc located near the middle of the building envelops. Site Observatiors: At the time of our visit to the site, we observed two exploratory pits dug about 60 fcet apart in thc proposed building area. Thc subsoils cxposcd in the piu, below about I foot of topsoil, consislcd of basalt rocks from gravel to bouldersizc in a whitish brown sandy silt matrix, About I foot of sandy silt and clay with scattered basalr rocks waq encountered in the upper, western pit overlying the basalt rocks. Digging in lhe basalt rocks was difficult and refusal to thc John Dcerc 60G mini-excavator w{s encountered in both pits at depths of 2 to 3 feet betow the adjacent ground surfacc. No free water wrs encountered in the pit crcavations and the soils were slightly moist to moist, The sitc slopes gcntly lo moderately down to thc south with a stecp 4 to S-foot high fill slope along Wood Nyrnph Road on the north side of the prop€rty. Thc site is vegetoted tr€ F*rkcr 3*3-f"'41 '? I l9 u el-ii+rr;:<,l* iipri;1g3 ? l?-fl:.,1"55SJ . $ilvcrrh.:u-:ri: S7*",tirg" I ?gii Ryan Pratt December2l,2015 Fage 2 with pinon ondjuniper trees. Basatt rocks were scattered about on the ground surface. Therc wos about 8 inches of snow cover at the time of our site visit. Resommendrtionsr Coosidering the conditions exposed in the pit excavations and lhe nlture of &e proposed construclion, spread footings plrced on the undisturbed natural basalt rosk soil can be designed for an allonnble soil bearing pressure of 3,09-S{fot support of the proposed residence. Our experience in this area is that a convcntional large excavatorcan get down about 2 feet frrrther in thc house excavation &an the refirsal depths crcountercd in the pits. Below that level and in narrow ulility trenches, blasting or chipping of the basalt rocks may be needed, Footings should be a minimum width of l6 inches for continuous walls and 2 feet for columns. Loose and dishubed soils in footing areas should be removcd and the bearing level extended down to the undisturbed natunrl soils. Holes below footing grade created by boulderremoval should be backfilled up to footing grade with consrete or imported sand and gravel such as % inch road base compactcd to at least 98% of the mocimum standard Proctor density. The bcaring soils should be protecled against frost and concretc should not be placed cn frozen soils. Exterior footings should be provided with udequate soil coverabove their beoring elevations for ftost protection. Continuors foundalion walls should bc rcinforccd top and bottom to span local anomalies such as by asruming an unsupporled length of at least l0 feet Foundation walls acting as relaining shuctures should also be designed lo rcsist a lateral enrlh pressure bns€d on an equivalent fluid unit weight of at least 50 pcf for on-site soil as backfill. A perimeter foundntion drnin should be providad to prevent lomporary buildup ofhydrostatic prrssurc behind the crawlspace or shallow basement walls and prcvent wetting of the lower level. Structural fill placed within floor slab areos can consist of thc on-site soils without topsoil, organics and rosk larger than about 5 inchcs (or a suitable imported material) compacled to at least 95% of stnndard Proctor density at a moisure content neof, optimum. Backfill placed around the smrcture should bc compaeted nnd the surface graded to prevent ponding within at lesst l0 feer of rhe building. The recommendations submitted in this letter are bascd on our observation of the soils ---^--l ..,:rL:- rL- -:r --^-.,-r!^-- -f ll-!r^l l^-rl. --l l- -^r:--1..1- ---L----c---vAlrurLs wtrltllr rlre |Jll 9Ar,svofllrllD t.rl llfllrlsLl sEPlll alll(l tlU lrgl lllUlUllE SUlrlUllll$E exploration down to the losded depth of foundation influence, This study is based on the assumption that soils beneath the pit dcpths have equal or bener support than those cxposed. The risk of foundation movement may be greaterthan indicated in this report because of possible variations in the subsurface conditions- In order to rcveal the nature JobNo. l15 J?54 Gfut Ryan Pratt December 21, 2015 Page 3 and extent of voriations in the subsurface conditions below the excavation, drilling would be required. It ls possible the data obtaincd by subsurface exploration could change thc rccornmendations contained in this lettcr. Ourservices do not include determining the prasence, prevention or possibility of mold or othcr biological contaminants (MOBC) developing in the frrture. lf the client is concerned about MOBC, then a professlonal in this spccial field of practice should be consulted- lf you have nny questions or need further assistance, please cdl our office. Sincerely }IEPWORTH - PAWI.AK GEOTECHNICAL, INC. Danicl E. Hardin, P,E. Rev. by: SLP DEFI/lsw Job No.I t5 575A e&frectr