The URL can be used to link to this page

Home My WebLink AboutSoils Report - Observation of Excavation 01.29.2008HEPWORTH - PAWLAK GEOTECHNICAL January 29, 2008 Scott Steele 4985 County Road 113 Carbondale, Colorado 81623 1 IL t I1h 1' 11%1 4. r ick,r4.4.h11r..11, In. 50:0 '011111v IL tiLl 15.1 l�I.n,4rkl G1:I111? , l:t.lorr 10 y104:11 Plume 970_945 74„ 1 -ax 1)70 9215 15.1 cul,nl Iy �n,•%+61 r�a�.h,c� r:n Job No. 107 0861 Subject: Observation of Excavation, Proposed Garage, 4985 County Road 113, Cottonwood Hollow, Garfield County, Colorado Dear Mr. Steele: As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on November 16, 2007 to evaluate the soils exposed for foundation support. The findings of our observations and recommendations for the foundation design are presented in this report. The services were performed in accordance with our agreement for professional engineering services to you, dated November 12, 2007. The results of our geologic site assessment will be provided under a separate cover. The proposed garage will be a single story, wood frame structure supported by a thickened -edge slab. Rigid foam insulation will be used for shallow frost protection. The uphill cut slopes will be retained by a 10 foot tall, cast -in-place concrete foundation wall. At the time of our visit to the site, the foundation excavation had been cut in 1 level between about 24 to 22 feet below the adjacent ground surface. Basalt rocks up to small boulder size were loosely stacked on the uphill cut slopes. The soils exposed in the bottom of the excavation consisted of basalt gravel and cobbles in a sandy clay matrix below up to about 1 foot of loose, disturbed on-site soils. The results of a gradation analysis performed on a sample ofsandy clay and gravel with cobbles matrix soils (minus 5 inch fraction) obtained from the site are presented on Figure 1. No free water was encountered in the excavation and the soils were slightly moist to moist. Considering the conditions exposed in the excavation and the nature of the proposed construction, a thickened -edge slab foundation placed on the undisturbed natural soil designed for an allowable soil bearing pressure of 1,500 psf can be used for support of the Parket. 303-1841-7119 • C:olin:do ,Shing, 719-613..5'71.62 • tiiheithlmu 971.4(- l9)M ) Scott Steele January 29, 2008 Page 2 proposed garage. The exposed soils tend to compress when wetted and there could be some post -construction settlement of the foundation if the bearing soils become wet. Footings (if any) should be a minimum width of 18 inches for continuous walls and 2 feet for columns. The loose and disturbed soils in the footing areas should be moistened and compacted prior to constructing footing forms. The bearing soils should be protected against frost and concrete should not be placed on frozen soils. Exterior footings should be provided with adequate soil cover above their bearing elevations for frost protection. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for on-site soil as backfill devoid of topsoil, vegetation and oversized rock. A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the uphill foundation retaining wall and prevent wetting of the lower level. Structural fill placed within floor slab areas can consist of the on-site soils compacted to at least 95% of standard Proctor density at near optimum moisture content. Backfill placed around the structure should be compacted and the surface graded to prevent ponding within at least 10 feet of the building. Cut and fill slopes should be graded to 2 horizontal to 1 vertical or flatter. A swale may be needed on the slope above the building to route surface water around the building. The following slope treatments are recommended as alternatives to retaining the steep slope with the building walls. 1) Timber crib retaining walls separate from the building. 2) Rock -filled wire baskets or gabions. 3) Mechanically stabilized earth (MSE) walls composed of compacted layers of soil reinforced with Tensar geogrid. These walls can be faced with timber cribbing, boulders or masonry. All retaining walls separate from the building should be designed for a lateral earth pressure based on an equivalent fluid unit weight of 45 pcf, Drainage should be provided behind the walls to reduce potential hydrostatic pressure. A swale may be needed uphill of the walls to route surface runoff away from the face of the retaining walls. Job No. 107 0861 G wtech Scott Steele January 29, 2008 Page 3 The recommendations submitted in this letter are based on our observation of the soils exposed within the foundation excavation and do not include subsurface exploration to evaluate the subsurface conditions within the loaded depth of foundation influence. This study is based on the assumption that soils beneath the footings have equal or better support than those exposed. The risk of foundation movement may be greater than indicated in this report because of possible variations in the subsurface conditions. In order to reveal the nature and extent of variations in the subsurface conditions below the excavation, drilling would be required. It is possible the data obtained by subsurface exploration could change the recommendations contained in this letter. 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. If you have any questions or need further assistance, please call our office. Sincerely, HEPWORTH - PAWLAK GEOTECHNICAL, INC. e V„.ce Trevor L. Knell, P.E. Reviewed by: Daniel E. Hardin, P. TLK/vad attachment Figure 1 - Gradation Test Results au .01101uwr .n D �s� • • - *443 Job No. 107 0861 HYDROMETER ANALYSIS I pq HR. TIME READINGS U.S. STANDARD SERIFS 0 45 MINASMIN.6DM,N19MIN.4 MIN. 1 MIN #200 *100 #50 #30 #16 #8 SIEVE ANALYSIS CLEAR SQUARE OPENINGS I 10 20 30 40 50 60 70 80 90 100 #4 3/6' 314' 11/2' 3' 5'6' 8' 100 al!laidaddadd Ed! r� a! aw.a !!al ra- !adomadalal PIM as^� waw —ate. wa- MEM MI! as --am! ME aa^ -ar at ate aa- a—ia arm aa - —. r_ ---a—.� —a a _ -am al --- !MINN am! a_a_ -- !Maal 11 a—a_ --El! -_-a_ al!! ----.. EM! la /MEI -aaa- �r — -- a_ -ate aaa - a_ E_ aaa r r�aaa- ---. rrrra !maw! !I! —a-a- a_ !,aa. Mad -- —a -- rr_ --•ter a_ aaa—rr s ME —a !IN --- �r� —a11 al — w aaa_ _a ---- !Mai!! - !!!!EL aala -- —— a_ a.� a— !!Ia r. ■� ! al r_ parr ___ 11 ,I1 a_ a! �-—aa__a_r -_ aaaaaaaa- a_ a_ a_ .— —arr aa_- —r----- a art _—Emma!rr a! III aa•---r—a w_—w---- ra -- Ela—!MIw�aaM_ a_ aaaa a►..— — tea.MEM r. —rra -_! -.+a as __ airy. -----_ a—M_ Ed EN! ria aa -r- aa- a_ tea_ a--_ a--_ -- w __-- al !I rrarr __rr 1•.IFamy5- r! --la!— --a_ -- !ar sem! ��-- .1r 0+.d Wadi �r-arr r_ a.^ a— —! --rrrr a_ � aa - !!MMI MIME a!aa i �r --!daanal 1!I MaNd —a_ �- —aa_ lard a _ --� as--arra a—M _ --a_ --ate a_ a rrr --aa-a_�..i_ --a_ --ate — —ate a__a__ -_ 1-_ a_ w -a— ar--_ aa--_ a --a --r_a —_r-rrrrra aMaa --l! .001 .002 .005 .009 .019 .037 .074 .150 .300 .600 118 2.36 DIAMETER OF PARTICLES IN MILLIMETERS 4.75 9.5 19.0 37.5 12.5 78.2 i27 2 203 CLAY TO SILT Frt SNA MEDIUM ICOaASE AWE 1 CHASE I GRAVEL 39 % LIQUID LIMIT % SAND 17 % SILT AND CLAY 44 % PLASTICITY INDEX % SAMPLE OF: Sandy Silty Clay and Gravel with Cobbles FROM: Bottom of Excavation, North side (Matrix) 107 0861 90 80 70 60 50 40 30 20 10 0 BIZ NT P. ► r, HCPWORTH•PAWLAMC GEOTECHNICAL GRADATION TEST RESULTS I Figure 1