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HomeMy WebLinkAboutBLDR-4-10-5921 Engr Soil evaluation 4-15-10.tif 04/23/2010 13:37 8283274941 SW ASSOCIATES INC PAGE 01/08 L ",j ASSOCIATES, NEW MNSTRIjCTJON • RENOVATIONS ADrx - rjoNS Date: Z To: G 1 t / From: Igo Number of pages to follow including cover sheet gj t. 735 ELEVENTH AVE. BLVD. SE J-UCKORY, NC 28602 PHONE 828- 327 -8627 FAX 828 - 327 -4941 04/23/2010 13:37 8283274941 SW ASSOCIATES INC PAGE 02108 April 15, 2010 Mr. Stan Whittington Sw ASSOCIATES, INC., fax 828 3274941 735 11"' Ave. Blvd. SE Hickory, NC 28602 RE: Report of Foundation Soil Evaluation Alkoutami Residence — Garage Addition Hickory, North Carolina Unifour Job Number 3529 Dear Mr. Whittington: As you requested, Unifour Engineering & Testing Laboratories, PC (Unifour) was retained to test and observe the shallow foundation soil for the Alkoutami Residence Garage Addition, located in Hickory., North Carolina. Unifour's scope did not include investigation of deep subsurface conditions or the development of engineering recommendations for foundation design. .0 Dynamic Cone Penetrometer (DCP) tests were performed in the soil within the foundation footprint of the proposed structure at the bottom of footing elevation (BOF) and as deep as 7 feet below BOF. The DCP test is performed by driving a 1 %inch diameter steel cone into the soil using •a 15 -pound weight falling 20 inches. The number of blows required to drive the cone 1 inches is designated as the Cone Penetrometer Resistance and is recorded in units of 'blows per increment' or bpi. The test procedure is described in ASTM Special Technical Publication STP -399. The DCP test values were correlated to an estimated Standard Penetration Resistance (N- value) based on the soil type, using procedures described in STP -399. The field data and estimated N- values are presented in the attached Report of Dynamic Cone Penetrometer Test forms. The foundation soil encountered at and below the SG at the test locations consisted predominately of sandy silt. The estimated N- values indicated in the DCP tests ranged from 1 to 13 blows per foot (bpf). The majority of the.estimated N- values were less than 6 bpf. mun i ' four 70t91atA�urr9u► • 111d�f. Nafh 2860) po. •b ,�rca�rgo• �zwsaao }tea esx� Engineering & Testing Laboratories, PC 04/23/2010 13:37 8283274941 SW ASSOCIATES INC PAGE 03/08 Foundation Sod EvaluatioII-3529 Apol 15, 2090 Alkoufand Residence- Garage. Hickory, NC Page 2 Conclusions of Bearing Evaluation Assessment According to information provided by the contractor, the foundation design and, footing widths for this structure are based on an allowable- soil bearing pressure of 2;000 pounds per square foot: Based on the DCP results and soil classifications, the foundation soil at the test locations and. depths are generally unsuitable for bearing support of the foundations as .currently designed. To minimize excavation needs and avoid excessive disturbance of soils at depth, Unifour recommends revision of the planned foundation and slab system into a monolithic foundation approach. By using a monolithic foundation system, the overall applied bearing stresses applied to the addition footprint can be significantly reduced ,to an affective stress on the order 750 psf or less. "Phis lower applied stress will minimize the detrimental affects of potential settlement from compression of the existing softer soils under load. Since bearing capacity of soil is partly a function of soil type and footing width, these test results should be considered valid only for the locations and elevations . noted at the time of our testing. It is important that Unftur be retained to bbserve all footing areas once they are opened and prepared to confirm that thdrecommendations presented herein are applicable to all exposed conditions. Conclusions of Impact Evaluation to the Existing Segmental Retaining Wall In addition to evaluating the. bearing support characteristics of the soils that will be exposed within the proposed garage addition footing lines, you have authorized Unifour to provide a generalized review of the new construction's potential impacts to the existing Segmental block retaining wall. As we noted in our original work authorization, Unifour Engineering & Testing laboratories, Inc. is not evaluating the construction of the existing segmental block retaining wall (methods or materials) itself, but rather what impacts might result from the new addition. For the purpose of our evaluation, we assume that the existing segmental - block retaining wall has been constructed in accordance with the National Concrete Masonry Association (NCMA) !. guidelines using approved materials. The existing SRW has obviously had some degree of detrimental settlement and /or displacement in -its history. As can be seen in the existing driveway irregularities and stress cracks, there has been either some excessive settlement of the backfrll behind the wall, some lateral displacement of the wall face itself, or more likely a combination of both. Our generalized analysis of the introduction of a limited line load stress at the planned foundation lines for the new addition would not . have a significant or detrimental affect on a typical Wall section constructed to NCMA standards. Our f a 04/23/2010 13:37 8283274941 SW ASSOCIATES INC PAGE 04108 Foundation Scut Evaluation -3529 ApdI 15, 2010 Alkoutaml Residence - Garage, Hkkory, NC page 3 concern, however, is that this retaining wall already has signs of past movement and the possibility for future setYement and /or lateral movement can not be eliminated. In the event the existing wall was to experience further movements or settlement, there is the possibility that such movements could negatively affect the bearing conditions beneath the new addition. It is our recommendation that SW Associates, Inc. advise the homeowner of the potential risk for adverse impacts to the new addition in the event of further movement of the existing SRW. If desired, Unifour can provide a separate scope of work to the homeowner for a thorough evaluation of the stability characteristics of the existing wall and make engineering recommendations to mitigate or remove future risks. If the homeowner chooses to forego any further evaluation of the existing segmental retaining wall, Unifour recommends that SW Associates, Inc. seek a specific waiver and release of liability for any consequential damages that may occur to the new addition as a result of future SRW movements. Respectfully submitted, UNIFOUR ENGINEERING & TESTING LABORATORIES, PC Bye CAI I SEAL Matthew D. Hartley, El Bo by L. Barnes, P.E. 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