Abstract: The geological and geotechnical investigations in the proposed tunnel in offshore terrain are very challenge and the construction risk is extremely high. It is therefore critical to accurately characterize the karstic rock. The crosshole seismic wave computed tomography method has the advantages of simple operate, high resolution and high accuracy and receives wide applications in the karst terrain investigations. However, its application in the offshore karstic terrain investigation has not reported. This paper presents a case history of geotechnical investigation of offshore karstic terrain investigation for the proposed cross sea tunnel. The principles, basic operation and applications of the crosshole seismic wave computed tomography method are introduced and the investigation results are satisfactory.

Key words: crosshole seismic wave method, computed tomography, offshore, karstic terrain investigations