Estimating depth to bedrock beneath pavement using the SRBA prototype

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2002

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This manual describes the setup and operation of the prototype Seismic Refraction Bedrock Analyzer (SRBA) and the analysis of data acquired with the instrument. The SRBA prototype (fig. 1) was constructed at the Bureau of Economic Geology to aid in the estimation of bedrock depths and seismic velocities beneath paved surfaces. It employs a fixed array of ground-motion detectors (geophones) and a movable seismic source to acquire seismic refraction data that can be analyzed to produce two-layer, planar models of seismic velocity changes in the near surface. The instrument was designed and constructed during studies completed for TxDOT to determine whether existing geological data could be used to estimate bedrock depth to allow better analysis of falling-weight deflectometer data (Paine, 1999; Paine and Murphy, 2000). To test the concept of acquiring usable refraction data on pavement, we deployed standard seismographs and detectors with variable detector spacings at various test sites. These studies indicated that seismic refraction data could be acquired on asphalt pavement, but that the acquisition system was cumbersome to deploy. The SRBA prototype, with its fixed and stowable geophone array, aluminum tripod geophone bases, custom geophone spacing, and fixed seismic source locations, is the first version of a refraction system optimized for use on pavement.

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