Enhanced Newmark method for seismic analysis of submarine slopes

Zangeneh, Neda (2003) Enhanced Newmark method for seismic analysis of submarine slopes. Masters thesis, Memorial University of Newfoundland.

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Abstract

Newmark method of slope displacement analysis has been extensively applied in many slope stability analyses. However, there are some limitations in Newmark method that may lead to non-conservative predictions of slope displacements. To provide more realistic predictions of slope displacements, these limitations are considered throughout the study for enhancing Newmark method. The following additions to the original Newmark method have been included in this study: 1) accounting for seismically induced excess pore water pressure build-up, 2) accounting for excess pore water pressure dissipation after the end of shaking, and 3) accounting for possibility of multiple failure surfaces. Those enhancements are briefly discussed hereafter. -- During an earthquake, non-cohesive soils may experience considerable pore water pressure build-up, which in the limit can lead to a state of zero effective stress and soil liquefaction. Therefore, in such a case, an effective stress approach should be used because a total stress analysis may give highly under-conservative results. In the present effective stress approach, the effects of excess pore water pressure and subsequent changes in soil shear strength are considered. -- Also, after the end of the strong shaking period, pore water pressure starts dissipating. Dissipation of excess pore water pressure causes the soil to regain part of its original shear strength and consequently, the yield acceleration increases and becomes positive. Therefore, in such a case, considering the effects of excess pore water pressure dissipation gives better estimation of permanent slope displacements after the end of shaking. In this study the effects of excess pore water pressure dissipation are also considered, based on the one-dimensional consolidation theory. -- In homogeneous soil deposits the displacements are usually dist1ibuted with depth. For such situation, the rigid block assumption may induce significant differences between actual and predicted slope displacements. Therefore, two moving blocks have been considered to mitigate this limitation of Newmark method. The model is able to reproduce the gradual deformation of soil with depth and therefore provide a more realistic prediction for uniform sand deposits. -- The proposed enhanced Newmark method has been implemented in a computer program.

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