Loading...
HomeMy WebLinkAboutSoils ReportGtech HEPWORTH - PAWLAK GEOTECHNICAL July 1, 2013 Michael Lauterbach P. O. Box 5026 Edwards, Colorado 81632 Mjlauterbach5026 a,gmail.com Hepworth•Pawlok Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970.945.7988 Fax: 970.945.8454 email hpgeoOhpgeorech.cum Job No. 113 242A Subject: Observation of Site Conditions and Presumptive Soil Bearing Pressure, Proposed Residence, Lot SD17 (formerly Lot L3), Aspen Glen, Sundance Trail, Garfield County, Colorado Dear Mr. Lauterbach: As requested, Hepworth-Pawlak Geotechnical has reviewed the subject site conditions with respect to providing a presumptive soil bearing capacity for a spread footing foundation to support the proposed residence. The findings of our site observations and preliminary 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 July 1, 2013. Proposed Construction: The residence will be about 2,500 square feet, one story, wood frame structure over a crawlspace. The attached 650 square foot garage will have a slab - on -grade floor. Foundation loadings are assumed to be relatively Tight and typical of the proposed construction. Site Conditions: We observed the site conditions on July 1, 2013. The lot is vacant and the ground surface appears to have been graded during original subdivision development. The terrain is relatively flat with a slight slope down to the south. Elevation difference across the proposed building is about 1 foot. There is an irrigation ditch along the east side of the lot that was running at the time of our site visit. The lot is bordered on the north side by Sundance Trail and to the south by a pond. The lots to the east and west are also vacant. The subsoils in this area typically consist of up to 5 feet of sandy silty clay overlying relatively dense gravel soils. Subsidence Potential: Aspen Glen Subdivision is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock, The evaporite contains gypsum deposits. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, sinkholes were observed scattered in the Aspen glen development. The nearest mapped sinkhole is about 700 feet Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989 Michael Lauterbach July 1, 2013 Page 2 to the northwest of this site. Sinkholes were not observed in the immediate area of the subject lot. Based on our present knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot SD17 is low and similar to other lots in the area but the owner should be aware of the potential for sinkhole development. Preliminary Recommendations: Based on the site conditions and our experience in the area, it should be feasible to support the building on lightly loaded spread footings with some risk of settlement. The risk of settlement is primarily if the bearing soils become wetted and precautions, such as positive surface drainage away from foundation walls and adequate compaction of foundation backfill, should be taken to prevent wetting. Differential settlement risk may also be from variable soil bearing areas. For preliminary design of the footings, an allowable soil bearing pressure of 1,500 psf can be assumed. We should observe the foundation excavation at the time of construction to evaluate the soil bearing conditions exposed. If the soil bearing conditions are different than assumed, the foundation may need to be re -designed. The spread footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. All topsoil and loose disturbed soils in footing areas should be removed and the bearing level extended down to the undisturbed natural soils. The footing subgrade should then be moistened and compacted. Exterior footings should be provided with adequate soil cover above their bearing elevations for frost protection. We recommend 36 inches of frost cover be used. Continuous foundation walls should be well 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, excluding topsoil and oversized rocks, as backfill. Any foundation walls acting as retaining structures should be provided with an underdrain system to prevent temporary buildup of hydrostatic pressure. Structural fill placed within floor slab areas can consist of the on-site soils compacted to at least 95% of standard Proctor density (SPD) at a moisture content near optimum. Backfill placed around the structure should be compacted to at least 90% SPD and the surface graded to prevent ponding within at least 10 feet of the building. Landscape that requires regular heavy irrigation, such as sod, and sprinkler heads should not be located within 5 feet of the foundation. Limitations: The recommendations submitted in this letter are based on our observation of the site conditions and our experience in the area, and did not include subsurface exploration to evaluate the subsurface conditions within the loaded depth of foundation influence. The risk of foundation movement may be greater than indicated in this report Job No. 113 242A Gettech Michael Lauterbach July 1, 2013 Page 3 because of possible variations in the subsurface conditions. It is possible the data obtained by subsurface exploration could change the recommendations contained in this letter. We should observe the foundation excavation at the time of construction to evaluate the soil bearing conditions. 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. We If you have any questions or need further assistance, please call our office. Sincerely, HEPWORTH -- PAWLAK GEOTECHNICAL, INC. Daniel E. Hardin, P.E. DEH/ljg mu ug R 61,48 re 9 24443 1,1/.617A.L. 1-6; kitionimotO Job No. 113 242A Gtech HEPWORTH-PAWLAK GEOTECHNICAL September 20, 2013 Michael Lauterbach P. O. Box 5026 Edwards, Colorado 81632 Mjlauterbaeh5026ggmail.corn Flcl'+,vrh•l',mI,I; [.ic•LIt'thniull. Inc. 5.020I ow') I:,.,,,I 1 i4 ( ihlltY, n,�l �I''I'Inka, 1. cul, ,I'fiilt, 81601 1'1L Ili"')ftp. ).45.7`�sti q70,943 -s434 mail: h� rr,n•Ilhr„rc�h.,..nn Job No. 113 242A Subject: Observation of Excavation, Proposed Residence, Lot SD17 (formerly Lot L3), Aspen Glen, Sundance Trail, Garfield County, Colorado Dear Michael: As requested, the undersigned representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on September 13, 2013 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 as additional services and in accordance with our agreement for professional engineering services to you, dated July 1, 2013. We previously provided presumptive soil bearing pressure for this project in a letter dated July 1, 2013. The proposed residence will be about 2500 square feet, one story wood frame structure over a crawlspace with an attached garage. Foundations were designed for an allowable soil bearing pressure of 1,000 psf. At the time of our visit to the site, the foundation excavation had been cut in one level from 21/2 to 4 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation consisted of mostly medium stiff, sandy silty clay. Results of swell - consolidation testing performed on a sample of the clay taken from the site, shown on Figure 1, indicate the clay soils have low compressibility under light loading and a low collapse potential (settlement under constant load) when wetted. The sample showed moderate to high compressibility under increased loading after wetting. The bearing soils below the eastern third of the residence, including the master bedroom and front entry, consisted of relatively dense, slightly silty sandy gravel with cobbles and small boulders. A small backhoe pit slug near the southwestern corner of the residence, showed the gravel soils to be about 3 feet below footing grade. 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 soils designed for an Parker 303-841-7119 • ( „lurado Springs 719-63.3-5562 • Silvcrthorne 970-468-1 Michael Lauterbach September 20, 2013 Page 2 allowable soil bearing pressure of 1,000 psf can be used for support of the proposed residence. The exposed clay soils tend to compress when wetted and there could be some post -construction settlement of the foundation if the bearing clay soils become wet. The settlement could be on the order of 1/2 inch and would likely be differential between the eastern master bedroom area and the rest of the house. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. Loose and disturbed soils in footing areas should be removed and the bearing level extended down to the undisturbed natural soils. Other recommendations contained in our previous report should also be followed. The recommendations submitted in this letter are based on our observation of the soils exposed within the foundation excavation. Variations in the subsurface conditions below the excavation could change the recommendations contained in this letter, If you have any questions or need further assistance, please call our office. Sincerely, HEPWORTH - PAWLAK GEOTCHNICAL, INC. \\\0\11111 ! I m l% esr e4�c4o J�rQ °0� Daniel E. Hardin, P.E 24,)374m.1 .,116/� y ,ev O . �io flllfffH111R11\\\ attachments Figure 1 - Swell -Consolidation Test Results DEH/ksw Job No. 113 242A Ge'Ptecn