Modeling the dynamic behavior of lightly overconsolidated soil deposits on submerged slopes

In recent years, the stability of submerged slopes of the continental shelf has emerged as a fundamental element in the assessment of risk and the prediction of performance for offshore structures, particularly for the complex network of pipelines carrying oil and gas from offshore drilling platforms. In addition to the obvious environmental disaster that could result from the failure of such oil/gas pipeline networks, the potential for damage from tsunamis generated by submarine slides has also focused the attention on seafloor stability.; This work focuses on the characterization of the response of normally consolidated to lightly overconsolidated soft clays in submerged slopes subjected to dynamic excitation. A reduced state of stress, replicated in the direct simple shear laboratory testing apparatus, that includes only a normal effective stress and a shear stress is considered sufficient to describe in situ conditions. The assumption is made that the dynamic loading consists of shear waves which propagate normal to the soil layering and result in an additional cyclic shear stress on the soil.; The work is divided in three separate, equally important and interconnected parts: (1) Data gathering: collection of data from element level tests to guide model development and validation. Some data were gathered from the available literature. In addition, a preliminary testing program was also conducted on Young Bay Mud and is presented here. The experimental program includes monotonic and cyclic tests with different initial conditions and takes advantage of the special features of the U. C. Berkeley bi-directional simple shear device. (2) Constitutive modeling: development of a simple effective stress constitutive relation capable of describing the response of soft clays under multidimensional simple shear conditions. In particular, the model is able to predict changes in undrained shear strength due to different initial conditions, and the development of excess pore pressure and shear strains under cyclic loading. (3) Global analysis: a one-dimensional seismic site response analysis program implementing the proposed constitutive laws was used to evaluate the boundary value problem of the submerged slope under earthquake loading.