GEOPHYSICAL SURVEY TECHNIQUES TO DETERMINE LENGTHS OF PILES AND DRILLED SHAFTS

Three different types of seismic techniques were tested to determine the lengths of pile(s) and drilled shafts of bridge bents in overconsolidated clay soils in the Houston, Texas area. These methods were the seismic-wave reflection survey (SWRS), the transient forced vibration survey (TFVS) and the parallel seismic survey (PSS). They were conducted at bridge bends located along I-45, southeast of downtown of Houston, and on existing half-scale foundations at the University of Houston national Geotechnical Experimentation Site (NGES-UH). The purpose of the tests was to ascertain whether any or all of these methods would be reliable in determining the lengths of old or poorly documented foundations whose lengths are not known in overconsolidated clays of the type typically found in Houston, Texas. All three methods measured the depths to the toes of pile groups or individual drilled shafts to an accuracy acceptable for most bridge maintenance purposes, within approximately 0.3 m (1.0 ft) to 1.1 m (3.6 ft) of the actual pile lengths shown on the as-built plans. The most accurate prediction was achieved with the SWRS tests, while the least accurate prediction was achieved with the TFVS test.