Synthetic Crosshole Tomography Studies of Bridge Foundation Sites in Karst Terrane

Seismic crosshole tomography systems for characterization of the subsurface at bridge sites in mantled karst terrane were evaluated in this study. There is great need for a reliable testing method to map competent rock and estimate pile tip elevations during design of a structure. Prior to conduct and detailed analysis of crosshole tests at actual bridge sites in karst, important “synthetic model” investigations were first undertaken. For purposes herein, “synthetic models” refer to earth models whose velocity profile is assumed or known a priori. The synthetic model studies conducted indicate that the crosshole system is capable of accurately identifying and delineating horizontal and slanted layer interfaces, and that the method can produce valuable information for subsurface profiles that include dropping and pinnacled interfaces, and anomalies such as boulders or cavities. Based upon these findings, it can be concluded that seismic crosshole appears to be technically feasible for developing basic layer structure and top of rock profile in karst terrane.