LABORATORY DETERMINATION OF COASTAL SEDIMENT MECHANICAL-PROPERTIES

This article describes a laboratory testing program on a very soft, fi ne-grained coastal sediment to investigate methods for characterizing both the physicochemical properties of the sediment and its stress-str ain-strength properties in the laboratory. The very soft consistency o f these coastal sediments presents a significant obstacle to obtaining valid mechanical properties from laboratory tests. Such properties ar e needed to develop constitutive models for interpretation of in-situ tests, prediction of penetrating object behavior, and estimation of la ndslide and erosion potential. After physical and chemical characteriz ation, the sediment from the Gulf of Mexico was tested using one-dimen sional consolidation and consolidated-undrained triaxial and direct si mple shear tests. Testing problems associated with the high compressib ility and low strength of this material were identified and some solut ions developed to mitigate their effects. The results indicate that, w hile better sampling procedures need to be developed consistent consol idation and stress-strain-strength parameters can be obtained. However , special testing considerations are vital including innovative tube e xtrusion and specimen trimming procedures to minimize sample disturban ce, high-precision measurement instrumentation and comprehensive error analysis to correct measured behavior. The article recommends additio nal research that is vital in order to reach more definitive and widel y applicable conclusions about coastal sediment behavior.