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The discontinuous deformation analysis (DDA) is a discontinuum-based method, which employs a penalty method to represent the contact between blocks. The penalty method is easy to be implemented in the program, but the contact constraint is only approximately satisfied. Penetrations between contacting blocks are unavoidable even if the penalty value is very large. To improve the contact precision in the DDA, an augmented Lagrangian method is introduced, which can make use of advantages of both the Lagrangian multiplier method and the penalty method. This paper provides a detailed implementation of the augmented Lagrangian method in the DDA program and compares it with the standard DDA on the computational efficiency and contact precision. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In the two-dimensional discontinuous deformation analysis (DDA), contacts can be generalized into three types: vertex to edge, edge to edge, and vertex to vertex. In the vertex–edge contact, the contact reference edge is clearly and uniquely defined, while the contact reference edge for the vertex–vertex contact is not unique, which will lead to an indeterminate state. The indeterminacy of the vertex–vertex contact is a well-known problem in both the continuum-based methods and the discontinuum-based methods. The standard DDA employs the shortest path method to deal with the indeterminacy in the vertex–vertex contact, which is sensitive to the choice of analysis parameters, such as the time step size, the maximum displacement ratio and the contact spring stiffness. Two enhancements to the shortest path method are introduced in this paper. The first enhancement employs a temporary vertex–vertex contact spring to determine the moving tendency among two contact blocks. The second enhancement uses the trajectory of the vertex during a time step to find the entrance edge when the moving vertex invades into the target block. Examples show that these two enhancements to the standard DDA code work well. [Copyright &y& Elsevier]

Drill and blast method has been widely used as an effective excavation method for underground rock caverns or tunnels. To achieve a good blast design, an understanding on the rock dynamic response and rock fragmentation process is important. In this paper, numerical simulations are performed on a typical parallel hole cut blasting based on the discontinuous deformation analysis (DDA). The blast loading is obtained from the explicit FEM code LS-DYNA and the dynamic response of the rock mass is modeled by the DDA. Different influence factors on rock fragmentation under the blast loading are investigated, including the different delay time and various rock mass properties. Such a study will have potential applications for better drill and blast designs. [ABSTRACT FROM AUTHOR]

Abstract: The discontinuous deformation analysis (DDA) has been widely applied for rock engineering problems due to its special features in modeling the discontinuous rock mass. A linear polynomial function is often used in the standard DDA to ease the complex contact determination between the blocks. This linear displacement function generates a constant stress field within a block, which cannot be effectively used to model the stress variation within a block and across the block interface, especially in the region with a large stress gradient. In this paper, a stress recovery procedure is proposed for those DDA blocks which are glued together. Such a procedure can improve the stress accuracy along the block interface, and can be used for more accurate contact determination. Two numerical examples are presented to study the stress accuracy of the proposed method, and the results show that the proposed stress recovery method provides a better accuracy than the direct DDA and the averaging method. [Copyright &y& Elsevier]

Apertures of rock fractures is frequently considered as one of the most important factors affecting grouting characteristics. The real fracture distribution, however, is inaccessible due to its complex intrinsic properties, making it cumbersome to directly assess its impact on on-site grouting. In this paper, we argued that investigation of the grouting characteristics of a fracture network with a priori aperture distribution is promising to be an alternative approach for understanding the linkage between fracture distribution and grouting characteristics. A grouting module based on the Discontinuous Deformation Analysis (DDA) was developed to explore the linkage, with transient flow of grout studied. It is found that the grout consumed by the preset fracture networks exhibits a lognormal distribution, in agreement with the statistics of grouting data from 1361 grout holes at the Jurong Rock Cavern (Singapore). The observed agreement can be treated as an indirect verification of the robustness of our proposed grouting module. As anticipated, the grouting characteristics are significantly affected by the distribution of fracture apertures and connectivity among fractures around an injection hole, which are controlled by the distribution parameters. The grouting features of some dominant fractures could represent that of an entire fracture network. [ABSTRACT FROM AUTHOR]