| Summary: | 碩士 === 朝陽科技大學 === 營建工程系碩士班 === 95 === In situ measurements of seismic wave velocities are performed by many organizations on a routine basis to determine the dynamic properties of soils and rocks for engineering analyses. One of the most widely used geophysical approaches to obtain the compression and shear wave velocity profiles of a site is the cross-hole method. The basic concept of the cross-hole method is very simple. That is, just pass the desired seismic waves over a given travel path and measure the travel time. The wave propagation velocities of each type can be calculated by dividing the travel distance by travel time. However, for very accurate assessment of the wave velocities, a proper source to generate the seismic wave is crucial.
The objective of this study is to develop a pneumatic hammer which can be used as a seismic source for cross-hole tests. The hammer utilizes compressed air to compress a spring through a piston. When the piston is released, elastic energy stored in the spring drives the piston back and expands the tip a wedge device to impact the wall of borehole casing. The main advantage of the new device lies in that the impact force produced by this hammer is directional. Therefore, it can generate primary P-wave when the tip is oriented toward the receiver and primary S-wave while the tip is oriented perpendicular to the receiver. Preliminary test results of this study indicate that, with the pneumatic mechanical hammer, identification of the first arrival of P-wave and S-wave is a lot easier than using the traditional seismic sources.
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