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Home My WebLink AboutObservation of Excavation 04.10.17H-PVKUMAR Gtolæhr{ctl Englnccdng I Erutnacdng G€ology Mabrlela Tesllng | Ënvlronmental 5020 County Road 154 Glenwood Spdngs, C0 81601 Phone: (970) 945-7988 Fax (970) 945-8454 Email: hpkglenwood@kumarusa.com Office Locatþns: Parker, Glenwood Springs, ard Summit County, Colorado April 10,2017 Darren Gallegos 1808 Ouray Road Glenwood Springs, Colorado 81601 darengallçggs@hotmail.com Project No. l7-7-290 Subject:Observation of Excavation, Proposed Residence, Lot 51, Filing 48, Oak Meadows Subdivision,394 Silver King Court, GarFreld County, Colorado Gentlemen: As requested, a representative of H-P/Kumar observed the excavation at the subject site on April 5,2017 to evaluate the soils exposed for foundation support. The findings of our observations and recommendations for the foundation design ûre presented in this report. The services were performed in accordance with our agreement for professional engineering services to you, dated April 5, zOn. Hepworth-Pawlak Geotechnical (now H-P/Kumar) previously conducted a geologic and subsurface study for Filing 4 development and presented the frndings in a report dated April 15, 1998, Job No. 196 420. The proposed residence will be a 2-story structure above a basement level with an attached garage at the main level. Garuge and basement floors will be slab-on-grade. Spread footings placed on gravel soils and sized for an assurned allowable bearing pressure of 2,500 þsf were designed for the foundation support. At the time of our visit to the site, the basement excavation and garage perimeter trenches had been cut in 2 levels from about 7 to 14 feet below the adjacent ground surface in the basement area and about 4 feet deep in the garage area. The step between levels was about 5!/z feet. The soils exposed in the bottom of the excavation consisted of silty clayey sandy gravel and cobbles with basalt boulders to typically 3 feet in size. There was considerable loose soil from the rough cut digging in the bottom of the excavation. Results of swell-consolidation testing performed on Darren Gallegos April 10,2017 Page2 a sample of clay taken from thc gûrsge floor area, shown on Figure l, indicnte the soils have low compressibility under light loading and a minor expansion potentiûl when wetted. The results of a gradation analysis performed on a sample of the gravel soils from the basement level (minus 5 inch fraction) are presented on Figure 2. 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 ûn the undisturbed natural granular soil designed for an allowable soil bearing pressure of 2,500 psf can be used for support of the proposed residence foundation. The clay soils tend to expand when wetted under light load and there could be some post-construction rnovement of the garage slab if the bearing soils become wet. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. LBose aq¿ or removed down to the _qndisturbed¡aturqlta{l-. .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 l2 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 granular soil as backflrll excluding rock larger than about 6 inches. A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the basement walls and prevent wetting of the lower level. The drain will need to outlet tCI a sump and pump below the basement level. Structural fill placed within floor slab areas can consist of the on-site granular soils compacted to at least 957o 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 l0 feet of the building. Landscape that requires regular heavy irrigation, such as sod, and sprinkler heads should not be located within l0 feet of the foundation. The recommendations submitted in this letter are based on our observation of the soils exposed within the foundation excavation and the previous subsurface information and do not include subsurface exploration at the subject site to evaluate the subsurface conditions within the loaded depth of foundation influence. This study is based on the assumption that soils beneath the Darren Gallegos April I0,2017 Page 3 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 rhe 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, plea.se call our office. Sincerely, H-P* KUMAR Steven L. Pawlak, P Reviewed by: DEH SLP/kac Attachments: Figure I - Swell-Consolidation Test Results Figure 2 - Gradltion Test Results cc Kurtz ¿nd Associates - Brian Kurtz (kr¡ftzengineer@v¿thoo.coq) Moisture Content = 16.7 Dry Density = 112 Sample of: Sandy Sitty Clay From; Garage Slab Area percent pcf Iì \I \ 'Expansion upon wetting èS É .p altÉ IEo.x LrJ I .9v,tt,c) ct Eô(J 0 1 2 3 01 1.0 10 100 APPLIED PRESSURE - KsI 17-7-290 H-P\KUMAR SWELL-CONSOLIDATION TEST HESULTS Figure 1 24 HÊ. 7 HR o 45 MrN, 15 MrN. TIME READINGS US STANDAFDSEñIES #50 #30 #16 t8 CLEAR SOI.JARE OPENINGS gMrN 4 M'N 1 MlN. #2fi¡ #1 #4 3/8', 314' 't ll?f 3. 5'6. 8.100 90 80 70 î0 2t) 30 ôy40 a lr, É. l- 50 zl,() É,l¿lo60 602 rnø o-50 t-z.l¡JC'Ê,l¡J 40û 7A 80 90 100 30 ?0 r0 000f 002 00S 009 019 .037 o74 .150 .300 .600 I r8 2.3€ DIAMEÍEF OF PABÍICLES IN MILL¡METEFS 475 95 190 375 125 76? t52 203 12f ct-AY to !"., I coüe.fs GRAVEL 51 7.SAND 22 %SILTANÐ CLAY 27 o/o LloulÐ LtMtT o/o PLASTICITY INDEX % SAMPLE OF: Silty Clayey Sandy Gravel with Cobbles FROM:Bottom of Basement Excavation '+-L--.-¡.¿+|.-.-+-_J_,¡l- --.¡---.¡t-_¡Jf-L---r-----J- | ' I -4..JÊ-.-a-J- --r_lÚ-}l 17-7-290 H-P*lgtVlAR GHADATION TEST RESULTS Figure 2