KWRRI Research Reports


The basic concepts associated with the sledge hammer seismic refraction survey are reviewed and a modified version called down hole shooting is discussed. The latter method has distinct advantages for rock surface profiling. These include: calibration at the end points of the survey, measurement of vertical wave propagation velocities directly, and having a refracted wave ray path for almost the entire survey length.

The down hole shooting seismic refraction survey has been simulated with the digital computer. The method can handle any shaped rock surface profile and generates corresponding travel time curves for the forward and reverse profile surveys. This program was used to systematically study the effects of anomalies on the travel time curves. A method of data reduction was developed that enables an estimate of the rock surface profile to be made from the travel time data. The procedure involves the use of a reference depth line which connects the end points of a survey and the travel time curves for this reference depth line.

Field tests were performed at four sites having soil and rock characteristics different from each other. Typical results are given. Rock surface profiles are estimated from the travel time curves using the procedure developed and these are compared with the depth to rock by proof drilling.

Finally, the sources of error are discussed and some limitations of use are presented. For the sledge hammer method to be used for rock surface profiling, the rock surface should be within 25 to 30 ft of the soil surface and the minimum width of solution channel that can be sensed with this method is on the order of two feet. Recommendations for additional research are also given.

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The work on which this report is based was supported in pa.rt by funds provided by the Office of Water Resources Research, United States Department of the Interior, as authorized under the Water Resources Research Act of 1964.