Abstract: The cone penetration test with pore pressure measurement (CPTU) has been widely used in geotechnical investigation under various conditions due to its advantages of simple and fast operation, providing continuous and repetitive data. With the increasing demand of marine resource utilization, the CPTU receives wider applications in the marine geotechnical investigation. This paper presents a case history of geotechnical investigation for an undersea tunnel alignment project across the Qiongzhou Strait. The evaluation methods of marine soil stratigraphy, shear strength of cohesive and the liquefaction of loose sand are presented and compared with other conventional field and laboratory test results. The results indicate that the application of CPTU in the marine geotechnical investigation has the characteristics of better reliability. Evaluation methods and the empirical relationships used in the case history can also be used in similar marine environment.

Key words: Qiongzhou Strait, Undersea Tunnel, Cone Penetration Test with Pore Pressure Measurement (CPTU), Empirical Relationships