Deep Downhole Seismic Testing for Earthquake Engineering Studies

Abstract eng:
Downhole seismic testing is one field test that is commonly used to determine compression-wave (P) and shearwave (S) velocity profiles in geotechnical earthquake engineering investigations. These profiles are required input in evaluations of the responses to earthquake shaking of geotechnical sites and structures at these sites. In the past, traditional downhole testing has generally involved profiling in the 30- to 150-m depth range. As the number of field seismic investigations at locations with critical facilities has increased, profiling depths have also increased. An improved downhole test that can be used for wave velocity profiling to depths of 300 to 600 m or more is presented. The improvements include: (1) a more powerful seismic source, (2) generation of a simple and readily-identifiable sinusoidal waveform, and (3) post-processing of the time-domain records to increase signal-to-noise ratios at deeper depths. The equipment, test procedure and signal processing used in the improved test are discussed. Examples of raw and processed time-domain records at depths ranging from 317 to 427 m are presented. P- and S-wave travel time plots and the interpreted wave velocity profiles measured to a depth of 427 m in one borehole are shown to illustrate the profiling capabilities.

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