Free fall penetration test the undrained shear strength of submarine sediments

Abstract

To perform in-situ testing of deep-sea sediment undrained shear strength, a novel free-fall penetrometer has been developed. This penetrometer is released from above the seabed and penetrates the sediments under gravity, resulting in intense interaction with the sediment. The study conducted free fall penetration tests in the Xisha area of the South China Sea, yielding the following achievements: (I) the establishment of a free-fall penetration governing equation, influenced by penetration attitude, along with the development of a model for undrained shear strength, revealed that at a 5° penetration angle, the sediment support force exceeded 100 N, and the undrained shear strength is approximately 40 kPa. (II) the relationship between dynamic penetration resistance coefficient and penetration velocity was inverted by the data from in situ test and laboratory. An error analysis revealed that inclined penetration and unreasonable penetration resistance coefficient can lead to errors exceeding 40 % in the test results.