Showing papers on "Discontinuous Deformation Analysis published in 2017"

Coupled time domain integration algorithm for numerical manifold method

Abstract: A temporal coupled explicit–implicit time integration algorithm is proposed to improve the computational efficiency of the numerical manifold method (NMM) for seismic stability analysis of rock slope. It includes a coupled time integration scheme, a phase transfer criterion, and an associated contact algorithm. To calibrate the proposed algorithm, a block sliding along a slope under seismic excitation and a block rocking under half-sine pulse shaking are simulated. The traditional limit equilibrium method (LEM) for slope stability analysis determines the factor of safety (FoS) without considering the time-dependent effect. The developed algorithm is able to simulate jointed rock slope seismic stability taking advantage of the NMM for continuous and discontinuous deformation analysis. An open-pit mine slope excited by the El Centro earthquake wave is studied. The simulated results are in good agreement with the results based on the traditional NMM, whereas the computational efficiency is improved s...

Dynamic simulation of landslide dam behavior considering kinematic characteristics using a coupled DDA-SPH method

Abstract: Landslide with significant volume and considerable velocity may block the river stream in the hillslope-channel coupling system, forming the natural dam and the dammed-lake behind. Previous studies predicted the behavior of landslide dams using different dimensionless indexes derived from the geomorphological characteristics. However, the kinematic characteristics of the river and landslide also play key roles in the dam formation. To consider the kinematic characteristics, the dynamic simulation of the dam behavior (formation and failure) involves three problems: (i) the movement of the river flow, (ii) the landslide movement and (iii) the landslide-river interaction. In this study, the movement of the river flow is simulated by a particle recycling method (PRM) under the framework of smoothed particle hydrodynamics (SPH). The discontinuous deformation analysis (DDA) is used to model the landslide movement. The interaction between the solid and fluid phases is achieved by the coupled DDA-SPH method. The proposed methods have been implemented in the numerical code, and a series of examples were employed for validations. The importance of the kinematic characteristics for the dam behavior was demonstrated by a series of numerical scenarios.

New geometric restriction for the displacement-constraint points in discontinuous deformation analysis

Abstract: A displacement-based seismic discontinuous deformation analysis (DDA) considers the influence of an earthquake by applying a time-dependent displacement constraint to simulate time-dependent ground movement of the base rock. However, unexpected variations of the base block stress and the block area in a seismic DDA may affect the block contacts with another block. This study theoretically clarifies the mechanism that causes unwanted base block distortion in a seismic DDA. A new geometric restriction is proposed for the assignment of displacement–constraint points to simulate the ground movement of two-dimensional (2D) and three-dimensional (3D) convex and concave blocks without changing the DDA algorithm. Additionally, the Daguangbao rock avalanche triggered by the Wenchuan earthquake in China is considered as a case study to demonstrate the capability of the new geometric restriction in a DDA to solve practical problems.

Advances in Two-Dimensional Discontinuous Deformation Analysis for Rock-Mass Dynamics

Abstract: This paper contains a summary of the developments and applications of the two-dimensional discontinuous deformation analysis (DDA2D) method regarding the modeling of rock-mass dynamics problems. Reviews on the control parameter value selections in DDA2D calculations and the developments and applications of the DDA2D regarding the analysis of rock slope failures, landslides, rockfall, some earthquake-related problems, and so forth, are performed. Research on the DDA2D for three basic rock-mass dynamics problems, such as block dynamic sliding, stress wave propagation, and dynamic fracturing, are specially stated. The modeling of rock blasting, a typical exact rock dynamics problem, is selected as a representative application example of the DDA method to be presented. Generally, the DDA2D has shown to be a powerful numerical method for the modeling of rock-mass dynamics. However, one should pay enough attention to the value selections of those important user-supplied control parameters, as well as to...

Parallel Computing of Discontinuous Deformation Analysis Based on Graphics Processing Unit

Abstract: The performance of discontinuous deformation analysis (DDA) needs to be improved for large-scale analysis. In this study, the contact detection and open-close iteration, as the bottlenecks of DDA computing, are reimplemented on graphics processing units (GPUs). For contact detection, the proposed parallel method accelerates DDA computing by maintaining a high loading balance and data reuse ratio on the GPU. The open-close iteration is divided into two parts, simultaneous equations solver and interpenetration checker. For the simultaneous equations solver, both the parallel Jacobi method and the block Jacobi preconditioned conjugate gradient (BJPCG) methods are implemented on the GPU to substitute the original successive overrelaxation (SOR) method. The parallel interpenetration checker is improved by optimizing conditional branches on the GPU. Two applications of the new parallel methods are introduced. The results showed that the broad and narrow phases of contact detection showed 18 and 5 times ...

Extension of the Discontinuous Deformation Analysis Method to Simulate Seismic Response of a Large Rock Cavern Complex

Abstract: The discontinuous deformation analysis (DDA) method calculates large deformations and discontinuous problems using time-step solving and provides an effective tool for analyzing the seismic response of rock mass engineering In this paper, extensions of the DDA method to simulate the seismic response of a large rock cavern complex are carried out First, applicability of the existing seismic input methods, including the multiblock Newmark method, large mass method, and large stiffness method, are discussed Second, considering the characteristics of the seismic response of a large rock cavern complex, a new seismic DDA model that includes a coupling model and a force-input method is presented Last, the extended DDA method is used for a case study Simulations of the quasi-static and seismic dynamic stages for the large rock cavern complex of the Dagangshan hydropower station in southwest China are carried out Considering the stress and displacement distributions in the quasi-static stage, the mo

Modeling of Rock Joints Under Cyclic Loading Conditions Using Discontinuous Deformation Analysis

Abstract: The shear strength of rock joints is an important factor to be considered when analyzing the stability of jointed rock mass. Rock joints tend to have smaller shear resistances in the reverse shearing than that of the forward shearing. A conceptual model describing the general shear behavior of rock joints under cyclic loading and the Barton–Bandis joint model considering the surface roughness degradation are implemented into the two-dimensional discontinuous deformation analysis (DDA) model. The modified DDA model is empirically validated by cyclic shear tests on two types of rock joints. Numerical simulations agree well with the experimental results, indicating that the DDA model is capable of describing the varying shear behaviors of rock joints subjected to cyclic loading conditions.

Independent cover meshless method for the simulation of multiple crack growth with arbitrary incremental steps and directions

Abstract: The independent cover meshless method (ICMM) defines mesh irrelevant and node-based polynomial meshless interpolation functions over independent covers of discrete nodes and thus possesses the distinguished features of a simple formulation, low computational cost, the accurate numerical integration, and the convenient numerical implementation. By utilizing the unified continuous and discontinuous deformation analysis based on the ICMM interpolation theory, this paper systematically studies the simulation of complex crack propagation, the accurate calculation of mixed-mode stress intensity factors (SIFs) and the influence of crack growth increment and mesh density on the computational accuracy and stability. In the present computing framework, cracks are allowed to grow in arbitrary directions with arbitrary assigned incremental lengths. This technique provides a simple, convenient and efficient numerical method for fracture and failure analyses of brittle structures. Numerical examples for the calculation of stress intensity factors and the simulation of crack propagation demonstrate the accuracy, effectiveness and robustness of the present method.

Discontinuous Deformation Analysis in Rock Mechanics Practice

Abstract: The numerical, discrete element, Discontinuous Deformation Analysis (DDA) method was developed by Dr Gen-hua Shi while he was working at the University of California, Berkeley, under the supervision of Prof Richard E Goodman in the late 1980s Two-dimensional DDA was published in 1993 and three-dimensional DDA in 2001 Since its publication DDA has been verified, validated and applied in numerous studies worldwide and is now considered a powerful and robust method to address both static and dynamic engineering problems in discontinuous rock massesIn this book Yossef H Hatzor and Guowei Ma, co-chairs of the International Society for Rock Mechanics (ISRM) Commission on DDA, join Dr Shi in authoring a monograph that presents the state of the art in DDA research A comprehensive discussion of DDA development since its publication is provided in Chapter 1, followed by concise reviews of 2D and 3D DDA in chapters 2 and 3 Procedures to select geological and numerical input parameters for DDA are discussed in Chapter 4, and DDA validation and verification is presented in Chapter 5 Applications of DDA in underground and rock slope engineering projects are discussed in chapters 6 and 7 In Chapter 8 the novel contact theory recently developed by Dr Shi is published in its complete form, for the first time This book is published within the framework of the ISRM Book Series and is the contribution of the ISRM DDA Commission to the international rock mechanics community

Three-dimensional DDA and DLSM coupled approach for rock cutting and rock penetration

Abstract: Rock cutting and rock penetration are typical problems in civil, mining, petroleum, and geothermal engineering disciplines. They involve dynamic fracturing and fragmentation of rock, high-speed movements of a cutter/impactor, and complex dynamic contacts between the cutter/impactor and the rock. In this study a new three-dimensional (3D) coupled approach is developed to address these problems. The distinct lattice spring model (DLSM) is used to simulate the dynamic fracturing process of the rock, and the discontinuous deformation analysis (DDA) is adopted to model the high-speed motion of the cutter/impactor. An explicit-implicit coupling scheme is developed to bridge DLSM and DDA. Moreover, to take account of interaction between DLSM and DDA, a 3D simplex sphere-to-block contact method is introduced. Finally, a number of numerical examples are conducted to verify the implementation of the coupled approach and its ability to model rock cutting and rock penetration problems.

Rock strata movement and subsidence based on MDDA, an improved discontinuous deformation analysis method in mining engineering

Abstract: In this paper, a new program MDDA (mining discontinuous deformation analysis) has been developed to simulate the continuous excavation process in mining engineering based on the existing discontinuous deformation analysis (DDA). Through MDDA simulation, both the real-time stress distribution and evolution of rock strata movement during the mining process could be effectively obtained. A simple example was used to test the effectiveness of MDDA. The calculation results from MDDA well agreed with the theoretical results of the example. MDDA was applied to simulate roof falling and stress field evolution during mining process. The lateral pressure coefficient almost had no influence on rock strata subsidence in spite of some influence on roof fracture mechanics. What is more, the strata subsidence laws of MDDA simulation were approximately consistent with the Universal Distinct Element Code (UDEC) and similar simulation results.

Advanced discretization of rock slope using block theory within the framework of discontinuous deformation analysis

Abstract: Rock is a heterogeneous material, which introduces complexity in the analysis of rock slopes, since both the existing discontinuities within the rock mass and the intact rock contribute to the degradation of strength. Rock failure is often catastrophic due to the brittle nature of the material, involving the sliding along structural planes and the fracturing of rock bridge. This paper proposes an advanced discretization method of rock mass based on block theory. An in-house software, GeoSMA-3D, has been developed to generate the discrete fracture network (DFN) model, considering both measured and artificial joints. Measured joints are obtained from the photogrammetry analysis on the excavation face. Statistical tools then facilitate to derive artificial joints within the rock mass. Key blocks are searched to provide guidance on potential reinforcement measures. The discretized blocky system is subsequently implemented into a discontinuous deformation analysis (DDA) code. Strength reduction technique is employed to analyze the stability of the slope, where the factor of safety can be obtained once excessive deformation of slope profile is observed. The combined analysis approach also provides the failure mode, which can be used to guide the choice of strengthening strategy if needed. Finally, an illustrated example is presented for the analysis of a rock slope of 20 m height inclined at 60° using combined GeoSMA-3D and DDA calculation.

Boundary Element based Discontinuous Deformation Analysis

Abstract: A Boundary Element based Discontinuous Deformation Analysis (BE-DDA) method is developed by implementing the improved dual reciprocity boundary element method into the open close iterations based DDA. This newly developed BE-DDA is capable of simulating both the deformation and movement of blocks in a blocky system. Based on geometry updating, it adopts an incremental dynamic formulation taking into consideration initial stresses and dealing with external concentrated and contact forces conveniently. The boundaries of each block in the discrete blocky system are discretized with boundary elements while the domain of each block is divided into internal cells only for the integration of the domain integral of the initial stress term. The contact forces among blocks are treated as concentrated forces and the open-close iterations are applied to ensure the computational accuracy of block interactions. In the current method, an implicit time integration scheme is adopted for numerical stability. Three examples are used to show the effectiveness of the algorithm in simulating block movement, sliding, deformation and interaction of blocks. At last, block toppling and tunnel stability examples are conducted to demonstrate that the BE-DDA is applicable for simulation of blocky systems.

Three-Dimensional Spherical DDA Method for Modeling Friction Problems

Abstract: Three-dimensional (3D) discontinuous deformation analysis (DDA) is very suitable for simulating large-displacement behavior of rock masses. One fundamental issue commonly encountered in 3D DDA is 3D friction problems. In this paper, a friction contact model based on 3D spherical DDA (SDDA) and the determination method of friction force direction is proposed for modeling 3D friction problems. Simulation results of three verification examples with available analytical solutions demonstrate the correctness of the friction contact model in 3D SDDA. Meanwhile, the simulation result of one application example, namely, a 3D-sphere natural-accumulation simulation, indicates that the friction problems of a 3D-sphere system can be modeled well by the proposed friction contact model. This work is helpful for solving 3D friction problems in discrete blocky systems.

The Unsaturated Hydromechanical Coupling Model of Rock Slope Considering Rainfall Infiltration Using DDA

Abstract: Water flow and hydromechanical coupling process in fractured rocks is more different from that in general porous media because of heterogeneous spatial fractures and possible fracture-dominated flow; a saturated-unsaturated hydromechanical coupling model using a discontinuous deformation analysis (DDA) similar to FEM and DEM was employed to analyze water movement in saturated-unsaturated deformed rocks, in which the Van-Genuchten model differently treated the rock and fractures permeable properties to describe the constitutive relationships. The calibrating results for the dam foundation indicated the validation and feasibility of the proposed model and are also in good agreement with the calculations based on DEM still demonstrating its superiority. And then, the rainfall infiltration in a reservoir rock slope was detailedly investigated to describe the water pressure on the fault surface and inside the rocks, displacement, and stress distribution under hydromechanical coupling conditions and uncoupling conditions. It was observed that greater rainfall intensity and longer rainfall time resulted in lower stability of the rock slope, and larger difference was very obvious between the hydromechanical coupling condition and uncoupling condition, demonstrating that rainfall intensity, rainfall time, and hydromechanical coupling effect had great influence on the saturated-unsaturated water flow behavior and mechanical response of the fractured rock slopes.

Shear Creep Simulation of Structural Plane of Rock Mass Based on Discontinuous Deformation Analysis

Abstract: Numerical simulations of the creep characteristics of the structural plane of rock mass are very useful. However, most existing simulation methods are based on continuum mechanics and hence are unsuitable in the case of large displacements and deformations. The discontinuous deformation analysis method proposed by Genhua is a discrete one and has a significant advantage when simulating the contacting problem of blocks. In this study, we combined the viscoelastic rheological model of Burgers with the discontinuous deformation analysis (DDA) method. We also derived the recurrence formula for the creep deformation increment with the time step during numerical simulations. Based on the minimum potential energy principle, the general equilibrium equation was derived, and the shear creep deformation in the structural plane was considered. A numerical program was also developed and its effectiveness was confirmed based on the curves obtained by the creep test of the structural plane of a rock mass under different stress levels. Finally, the program was used to analyze the mechanism responsible for the creep features of the structural plane in the case of the toppling deformation of the rock slope. The results showed that the extended DDA method is an effective one.

Method for Estimating Normal Contact Parameters in Collision Modeling Using Discontinuous Deformation Analysis

Abstract: This paper presents a contact parameter estimation method for collision modeling using discontinuous deformation analysis (DDA). Most DDA codes and discrete element method (DEM) codes use the viscoelastic contact model for contact-stress calculation. The contact parameters of the viscoelastic contact model, such as normal stiffness and damping constant, affect the computation results observably. Although the DDA method has been proposed for more than 20 years, the contact parameters in DDA modeling are still difficult to determine. In collision dynamics, the coefficient of restitution (COR) is considered the critical parameter for describing the changes of motion state after collision between two objects. In the proposed method, the normal COR is used for evaluating calculation results of rockfall modeling with three-dimensional DDA. The normal COR of the two-object model is obtained by tests or empirical methods. The relation curve of contact parameters and the normal COR is generated on the basi...

Slope-Slide Simulation with Discontinuous Deformation and Displacement Analysis

Abstract: The discontinuous deformation and displacement (DDD) analysis method, a combination of the realistic failure-process analysis (RFPA) and discontinuous deformation analysis (DDA) methods, offers an appropriate approach for whole rock failure-process analysis involving both the small deformation and large displacement stages. A high rock-slope slide at the Alpetto Mine in Cesana Brianza, Italy, was simulated with the DDD method, and the results are consistent with site observations and previous numerical results, which validates the DDD code for this kind of geotechnical problem. Moreover, this study verified the two main advantages of the DDD method, i.e., the critical failure surface can be obtained directly without any assumptions with the RFPA module before using the DDA module, and computing efficiency is improved significantly because the large displacement elements are the only elements that need to be calculated by the DDA module. The DDD method has proved to be an effective and efficient a...