State of the Art: Laboratory Determination of the Strength of Marine Soils

The steps and procedures used to obtain submarine sediment shear strengths from laboratory tests on samples are reviewed and evaluated. These steps and procedures include sampling, handling, testing, and interpretation. Sampling causes the most uncertainty through the introduction of varied amounts of coring disturbance. The selection of the appropriate test and testing strategy is next in importance. Laboratory vane shear and other strength index tests are reviewed in detail because they have dominated the field for many years even though the results therefrom often differ from field behavior by a factor of up to two or more. Advanced tests, including triaxial and direct simple shear are gaining popularity. Two common strategies for these tests are the normalized soil parameter (NSP) method and consolidation to in-place overburden stresses. Both strategies require high quality samples, but extending the NSP approach to somewhat disturbed samples often may be possible. Cyclic loading dominates marine geotechnical problems and requires special consideration. Cyclic triaxial and direct simple shear tests are being used together with several empirical rules for interpreting their significance. Calcareous and gas charged sediments are common in the oceans and have unique and poorly understood properties. For all soils, producing the best laboratory strength data requires high quality push sampling, preferably augmented with a piston.