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HomeMy WebLinkAboutB14-0075 Foundation Inspection letterMay 20, 2014 Blueprint Construction Attn: Mike Rookey 193 Soda Creek Court Dillon, Colorado 81435 �1 Job No. 114 068A Subject: Observation of Excavation, Proposed Addition to Kent Johnson Residence, Lot 5, Bighorn Estates, 4238 Nugget Lane, Vail, Colorado Gentlemen: As requested, a representative of Hepworth - Pawlak Geotechnical, Inc. observed the excavation at the subject site on May 15 and 20, 2014 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 observations were performed in addition to and in accordance with our agreement for professional engineering services to Blueprint Construction, dated March 14, 2014. The proposed addition will be attached to the south and west sides of the existing residence. Spread footings placcd on the natural soils and sized for an allowable bearing pressure of 2,000 psf were assumed by the structural engineer for the building support. At the time of our initial visit to the site, the addition excavation was mostly complete and had been cut in 2 levels from 5 to 15 feet below the adjacent ground surface. The northern part of the addition area had not been excavated. The step in grade was about 3 Feet down at the north end. When observed on May 20, the remaining north part had been completed except for a large boulder in the north wall line. The soils exposed in the bottom of the excavation consisted of silty clayey sand with gravel. Samples of the sand were obtained for standard properties testing with the results presented in Table 1. No free water was encountered in the excavation and the soils were slightly moist in the north part and moist in the mid to south part. Footings of the existing residence were exposed Blueprint Construction May 20, 2014 Page 2 in the excavation. We are unaware of any foundation related problems with the existing residence. 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 2,000 psf should be adequate for support of the proposed addition. Dowling into the large boulder and eliminating the footing where needed is acceptable from a geotechnical viewpoint. The bearing soils could tend to compress when loaded and wetted and result in some post - construction settlement of the foundation differential across the addition and with respect to the existing building. Loose disturbed soils in footing areas should be removed down to the undisturbed natural soils or moistened and compacted. 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 55 pcf for on-site soil as backfill. 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. Structural fill placed within floor slab areas can consist of the on -site sand soils compacted to at least 95% of standard Proctor density at a moisture content near optimum. A minimum 4 -inch thick free draining gravel layer should be provided below the basement floor slab and connected -to the perimeter subdrain. 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 Job No. 114 068A GiL-Rech Blueprint Construction May 20, 2014 Page 3 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. Steven L. Pawlak, Rev. by: DEH SLP/ksw Attachment: Table 1— Summary of Laboratory Test Results cc: Boyle Engineering — Tim Boyle (bo l� eeng_@gwestoffice.net) Job No. 114 068A GE CgteCh co 0 �r H �F O z 0 Z -� LU Q � U_ Z Vj ui 0 0 uj o 0 d o ca LL1 LL = o F C) Q 'o 2 CL C W = N w a 0 U .J K m � � t� CC U U zc LU w i OZ d O H � U v x � a - c� z m t- w Q a F O w Zz> LU CIA a Q N CL < ao Z N 0 F J ci v= z �o 0 00 z� v uj F H Z ` 06 z o .--i 0 0 w W W o w 0 N w B14 -0075: Entries for Item:20 - BLDG - Foundation /Steel 14:39 06/05/2014 Action Comments By Date Unique_ Key DN engineering required : cmu walls are hollow, sgremmer 06/04/2014 A000179 and epoxy connection per plan can not be 798 completed Gas pipe is running through N. wall excel to relocate pour at own risk. All rebar is installed Der Dlans Total Rows: 1 Page 1 T. Boyle Engineering, Inc. 1650 Fallridge Road, Unit C -2 Vail, Colorado 81657 970/476 -2170 June 4, 2014 TOWN OF VAIL BUILDING DEPT. 75 S. Frontage Road West Vail, Colorado 81657 Subject: Dowel Connection Revision Johnson Residence Addition 4238 Nugget Lane Vail, Colorado To Whom It May Concern:: This is to confirm that I have approved a modification to the dowel connections between the new foundation walls and the existing foundation at the above noted residence. The contractor has discovered that the new foundation walls abut an existing hollow CMU foundation. Therefore, the epoxy grouting that was originally specified on Sheet S I will be inappropriate for this condition. I have instructed the contractor to use the same dowel size, length and spacing, but to grout the hollow cells solid that will receive these dowels. These hollow cells should be filled with grout from the top of the new foundation walls down to the existing footing. Please give me a call if you T. BOYLE ENG Timothy M oyle, P.E. President •• on this matter.