Abstract: The karst geology poses a potential safety hazard for the bridge engineering. It is therefore critically important to detect and to evaluate the karst rock cavities underneath the proposed bridge foundations. The conventional test boring method is very difficult to define the karst features as well as the horizontal and vertical limits of the karstic rock boundaries. The crosshole elastic wave Computer Tomography (CT) technique can capture the threedimensional distribution of the karst features, which is based on the differences of elastic wave prorogating in different geological materials between boreholes. This approach has the advantage of higher accuracy in positioning the space locations, higher resolution and it is well suited in the accurate positioning of the suspected karstic cavities in local areas underneath the bridge foundations. A case history of detecting the karst features underneath a proposed foundation is presented in the paper. 

Key words: Elastic Wave CT, Bridge Piled Foundations, Karst Rock Cavities, 3D Distribution