2001 Geotechnical Evaluation Report

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RVC Homes Project BABX-01-0124 April 12, 2001 Page 5 • C.4. Pile Foundations We have reviewed several pipe pile sizes that are commonly used to provide the recommended pile capacities in soil conditions similar to this project. Other suitable pile types may also be available and pile-driving contractors often offer alternate pile as part of their bid. If an alternate pile type is proposed, we would be pleased to provide our analysis and opinion as to the suitability of the alternate pile for the project. We chose two commonly used pipe sizes for our analysis,they are 12 3-4-inch OD and 9 5/8-inch OD pipe. These pile sizes also correspond to those offered by Atlas Foundation Company. C.4.a. Allowable Positive Geotechnical Capacities. Allowable positive geotechnical pile capacities are determined by dividing the ultimate positive geotechnical pile capacities by a factor of safety. The American Association of State Highway and Transportation Officials (AASHTO) recommend the safety factor be related to the degree of construction control. A listing of the factors of safety is provided in Table 1. Table 1. Recommended Factors of Safety Specified Construction Control Factor of Safety Dynamic formula 3.50 Wave equation(computer analysis with hammer and driving data) • 2.75 Wave equation and Pile Dynamic Analyzer(PDA) 2.25 Static load test and dynamic formula, wave equation and/or PDA 2.00 Wave equation. PDA and static load test 1.90 Based on Table 4.5.6.2A of AASHTO's Standard Specifications for Highway Bridges, 1996 C.4.b. Ultimate Positive Geotechnical Capacities. We used a combination of methods including DRIVEN to predict the ultimate positive geotechnical vertical static capacities of piles. DRIVEN is a computer program developed for the Federal Highway Administration. We assumed the pile cut-off elevations will be approximately 4 feet below the lowest level slab elevation; i.e., we assumed the cutoff elevations will be about 929. We also assume a static pile load test would not be economically feasible for a project of this size, therefore pile lengths given assume the AASHTO recommended safety factor would be 2.25 when using the wave equation analysis and dynamic pile testing to judge pile capacity.