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Unformatted text preview: X1 SITE EXPLORATION (Your site is probably not homogeneous, elastic, or isotopic.) Purpose gather data for foundation design and construction methods o Identify soil type, especially difficult soils such as soft clay, expansive clay, or muck o Determine layering (stratification) and variability o Obtain samples for identification and lab tests to measure soil properties o Determine depth to rock (if present) o Perform insitu field tests for soil properties o Observe site drainage conditions o Observe nearby structures possibly affected by construction effort o Measure depth to water table (effective stresses......) Planning an Investigation o Obtain information about site usage and design of structure (often preliminary). Compile best information about anticipated foundation loads (moving target). Consider building code requirements (can be restrictive). Anticipate construction difficulties (excavation, fill requirements, drainage, cofferdams, shoring). o Collect existing information: s Geologic survey maps type and age of soil/rock formation, faults s Geodetic survey maps land form, elevation, topography, site access s Specialty maps seismic potential, frost heave potential, flood zones s Aerial Photographs land form, sinkholes, lineaments, a picture is worth ..... s Soil survey maps information about surface soils (<10 depth) s City, county, state maps & documents radon potential, previous soil investigations, title history (previous owners - environmental hazards). s Adjacent site information geotechnical reports, permit applications o Field trip visit site, observe current usage, nearby structures/problems, type of vegetation, nearby cuts, accessibility o Detailed site investigation - develop information for foundation design s Start with a few preliminary strategically located borings/soundings. s The final number and depth of borings/soundings, and the amount of lab testing is based on the results obtained a work in progress. Include client in these decisions. Actual site usage may depend on results of the investigation. Some sites just arent worth the effort. s Minimum number of borings: one in center of each structure (building, pier, tower, etc.) Prefer 45 borings for buildings, 2-3 for large bridge piers. s All borings/soundings should penetrate to at least depth of 10% stress increase (2B). A few may be deeper, especially for large or heavy structures. For deep foundations penetrate 1B-2B (width of pile/shaft group ) below tips. s No hard rules. Geotechnical engineers have high professional liability rates because early mistakes may affect the entire project from the ground up....
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- Fall '08