The SHANSEP concept, developed by Charles Ladd and Roger Foott, has become one of the underpinning foundations of stability evaluation in engineering practice. It is based on the principle that the strength properties of mechanically compressed, fine-grained sediments normalize with consolidation stress. Further, this basic strength principle is codified in many soil models, including Modified Cam Clay and MITE3.
Amazing advances in technology have increased borehole drilling capabilities to nearly 40,000 ft. In the Gulf of Mexico, sediments are normally consolidated to great depth but have extreme excess pore pressure and complex states of stress due to salt deposit modification. Predicting the in situ stress state is necessary for accurate geophysical interpretation, as well as effective borehole design. Clearly, the mechanical behavior of the sediments is extremely important to these predictions.
Recent advances in experimental technology have enabled a detailed study of the compression, permeability, and shear behavior of materials over a wide range of stresses. In combination with resedimentation, we have been able to study these behaviors for a wide range of soils without dealing with the complexity of sample disturbance or specimen variability.
This lecture presents results of an extensive experimental program that establishes a new understanding of the variation in behavior as a function of stress and plasticity. Trends in mechanical behavior are very consistent with liquid limit. One very important outcome is the observation that clay rich sediments do not follow the rules of normalized behavior. This has resulted in a significant modification to the SHANSEP equation and created a need for a new generation of soil models.
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