This study examines the shear strength behavior of two mudrocks from the Gulf of Mexico through a series of KO-consolidated triaxial compression tests. The tests are performed over a very wide range of effective stresses from 0.1 up to 10 MPa. Samples were prepared for triaxial testing by laboratory resedimentation of the core material. There is a consistent decrease in the critical state friction angle of both mudrocks with increasing stress level, and this corresponds with an increase in the value of KO (the ratio of horizontal to vertical effective stresses for one-dimensional consolidation). The strength behavior of the Gulf of Mexico mudrocks is consistent with that observed for other materials from a wide variety of geologic backgrounds. It is shown that variations in critical state friction angle with stress level can be correlated to a mudrock’s liquid limit, an easily measured index property which reflects the clay mineralogy and clay fraction of a mudrock. This finding has great practical value as it allows for a reasonable estimate of the critical state friction angle of a mudrock without having to obtain intact field samples, which is frequently infeasible in the case of deep sediments or sediments from the deep ocean.


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