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Home My WebLink AboutObservation of Excavation 10.19.2016H -P V KUMAR Geotechnical Engineering I Engineering Geology Materials Testing Environmental 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax: (970) 945-8454 Email: hpkglenwoodekumarusa.com October 19, 2016 Town of Carbondale Attn: Jeff Jackel 511 Colorado Avenue Carbondale, Colorado 81623 (i iackel @carbondaleco.net) Office Locations: Parker, Glenwood Springs, and Silverthome, Colorado Project No. 16-7-534 Subject: Observation of Excavation, Proposed Announcers Booth, Carbondale Rodeo Grounds, County Road 100, Garfield County, Colorado Dear Mr. Jackel: As requested, a representative of HP/Kumar observed the excavation at the subject site on October 18, 2016 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 the Town of Carbondale, dated October 18, 2016. The proposed announcer's booth will be an elevated wood frame structure with slab -on -grade floor below. The booth will be located at the western end of the arena. At the time of our visit to the site, the foundation excavation had been cut in one level about 5 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation consisted of dense silty sandy gravel with cobbles. The results of a gradation analysis performed on a sample of silty sandy gravel (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, spread footings placed on the undisturbed natural soil designed for an allowable soil bearing pressure of 2,500 psf should be adequate for support of the proposed announcers booth. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils in fooling areas should be removed and the bearing level extended down to the undisturbed natural soils. 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 10 feet. Foundation walls acting as retaining structures (if any) should also be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 45 pcf for on-site soil as backfill. Structural fill placed within floor Town of Carbondale October 19, 2016 Page 2 slab areas can consist of the on-site soils compacted to at least 95% of standard Proctor density at a moisture content near optimum. Backfill placed around the structure should be compacted and the surface graded to prevent ponding within at least 10 feet of the building. 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, H -Pt KUMAR Louis Eller Reviewed by: •ya Daniel E. Hardin, F.E. ° 24443 • attachments Figure 1 - Gradation Test Results LEE/ksw H -P KUMAR Project No. 16-7-534 N RETAI, HYDROMETER ANALYSIS I SIEVE ANALYSIS i 24 R 7 NR TIME READINGS U 5 STANDARD SERIES 1 CLEAR SQUARE OPENINGS I p 45 MIN 15 MIN 6OMINI9MIN.4 MIN 1 MIN 0200 0100 050 030 *16 0B aaa� 10 20 30 40 50 60 70 BO 90 100 Spa axil. a Sala aa a— aaat- •a— SW= Salami aaa a-aaa a/■a- as. - a.r- ia�- a a a a -a-_ aa— aa� a as aa-aaaa=MN — Mama aa -as al -a- ^al�aa = a al a aal saa la aa- aa-- —aa— aaaa- ma aa- r a a — �- aaaaaaialaYanima - aaa Gaal- a as ala alar . as - as. 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Is Sal a al ala -a as aa_aa-- al aa a al Sal SE. - Sal aa-- a as rSIMS' -r- —�—�'.a. aaar- - — aJ'�i i �a� __- `i—r aaa .. -- ta•ll aa- r_—_ a as a -lila - a - -r arra - arm a as -ala - a as - - 'r i S`rr—arr— _ -a- aaaas-- aaa•al alai ar iaaa -a aa- aaaarra- a-aala ar r--Y.-r- s-i ala aari-a aa-- •aa♦ aa -a as f Sas ala SI r aaais —a Saltea- arilalaalaiaas_arra-a- aaaa--..111.1iIMI MN= a!_MEM -r— a liana alar Gall _ a lar a._ a ala rs as a - Pala as -i ala a.a ala Sal -a- WAS am_ '.aa—iaa—alai--w al.____ — — M-- • aa- a S/a all_ -awl -r- aa aas.aaaa aala a, MS as -aa -as -`ala Ai __- - aa_alaas-`a __ _rrar - aa-aa� Si - a — aasaa-aa- aaaaa� +a =aa Sa alar-a- aaa.- ala aa- ala aa- a._ as i as-- a - aa -alas -a-a-a-a-r� alma SI as-- a as ala ala -a - ala aa --=Ma MS aaaa-Mil -a- aaaaa — —a — aa- �- a a ala♦ ala -a SI SIM Pala ars aaaai-a- aaa.- -a- aa-- as a -a. -a- aaa—�- aaaii Ma= — aaaa as --sal aaaa— as—aaaa— as—aa-- aa—aaaaalr ala arra as lar alar - ala aa— Nal ✓arra rr-llll- a as arm SEW .a. a- a as aaq{alaa� ala ala -a— 001 002 005 009 019 037 074 150 300 600 116 2 36 DIAMETER OF PARTIC. ES N MILLIMETERS 4 75 a ala 9� 190 1i 5 37 5 —a- -a- -a- -r- -r as aala -r- 76 2 152 203 127 QAT P. 7L :.nen IM IILU rP1n4C4 1 , !1 r-.Atiorri 1 L..4.C,r IL71Hrs GRAVEL 55 % SAND 25 °o SILT AND CLAY 20 °o LIQUID LIMIT % PLASTICITY INDEX % SAMPLE OF: Silty Sandy Gravel with Cobbles FROM Bottom of Excavation 100 90 80 70 60 50 40 0 16-7-534 H-PKUMAR GRADATION TEST RESULTS Figure 1