Discontinuous Deformation Analysis With Strength Degrading Interface Model

Discontinuous deformation analysis (DDA) has been widely applied in simulations of discontinuous blocky systems. The behavior of a discontinuous blocky system is mainly governed by the strength of the interface joints. This thesis evaluates DDA’s accuracy of the critical stability analysis and its ability in simulating failure processes of the blocky systems, with the focus on its interface strength model.Firstly, the Mohr-Coulomb joint failure criterion, adopted in the original DDA (Shi[1]), is examined through a classic case of a single block on an inclined plane. It shows that when interface cohesion exists, the block may be unstable even if the interface strength is greater than the theoretical strength required for critical stability, as the cohesion has been improperly removed. The development of DDA with displacement-dependent interface shear strength (i.e., strength degrading interface model) is presented in this paper. Adopting relative displacement between contacted blocks as the criterion for the removal of cohesion will provide more accurate results.The modified interface shear strength model can also consider strength degradation of the materials, to simulate progressive failures of the landslides. To implement and illustrate the modified algorithm, two examples of progressive landslide failure simulations are performed. Both systems exhibit a two-stage failure pattern:a relatively slow, downward progressive failure stage followed by a rapid, massive run out failure stage.In addition, on the basis of Rankine’s and Coulomb’s earth pressure theories, a method to simulate soil in DDA is proposed. With the use of the modified DDA. failure mechanism and stability of the ancient seawall structure of the Qiantang River under various actual cases are analyzed, for the sake of providing some guidance for the conservation and maintenance of the ancient seawall.