Showing papers on "Discontinuous Deformation Analysis published in 2020"
TL;DR: In this paper, the authors presented the first numerical simulation of the post-failure behavior of the mining-induced landslide at the Nattai North site, and showed that the slope with inward sub-horizontal bedding planes and subvertical discontinuities remained stable if the mininginduced high principle stresses did not fracture the rocks near the slope toe.
46 citations
TL;DR: In this article, a coupled Discontinuous Deformation Analysis (DDA) and Particle Hydrodynamics (SPH) method is proposed to simulate the landslide failure process.
Abstract: Landslides involving solid–fluid interaction such as submarine landslides and landslide dams occur frequently around the world, which may bring severe damage to human lives and properties. Investigation of such landslides is thus of significance to hazard prevention and mitigation. To conduct the analysis, there are three key points to be addressed: (a) the landslide failure process, (b) the free surface flow, and (c) the solid–fluid interaction process. Discontinuous deformation analysis (DDA) method is suitable for analyzing discontinuous blocky systems and has outstanding advantages in simulating the landslide failure process. Meanwhile, smoothed particle hydrodynamics (SPH) method is well-suited for modeling the free surface flow. However, the consideration of solid–fluid interaction in these two methods is seldom, which somehow restricts their applications. With the aim to take advantages of these two methods, a coupled DDA–SPH method in two-dimensional case is proposed, in which the solid–fluid interaction is forced using a penalty approach. The SPH formulations are implemented into DDA code. Several numerical examples are presented to check the validity of the proposed method. A dam-break test is first investigated to show the success of implementing SPH into DDA code for modeling the fluid flow in later simulations of fluid–solid systems. Subsequently, the performance of the coupled DDA–SPH method is validated through a submarine rigid landslide, and the simulation results are in good agreement with the experimental data. Further, an extension study on the submarine deformable landslide is performed, in which the landslide mass consists of multiple blocks and a sensitivity analysis on the interface friction angle between blocks is conducted. Finally, a designed landslide dam is simulated to show the applicability and feasibility of the coupled DDA–SPH method.
45 citations
TL;DR: In this paper, the authors used Discontinuous Deformation Analysis (DDA) to simulate a tunnel excavation under various conditions (e.g., different dip angles and locations of the tunnel in the slope).
39 citations
TL;DR: A new contact potential based three-dimensional discontinuous deformation analysis method (3D-CPDDA) is developed that retains the advantage of the original DDA method in defining local displacement functions on a single patch, but also integrates the simplicity and rapidity of potential based contact processing.
38 citations
TL;DR: In this paper, a deformation-controlled rock bolt (DC-bolt) was proposed to prevent large tunnel deformations caused by the rock bursts or the squeezing ground conditions. But the performance of the proposed DC-bolt was verified by the numerical simulations using the discontinuous deformation analysis (DDA) and by the prototype laboratory tests.
29 citations
TL;DR: The explicit DDA that uses an explicit time integration procedure and an explicit calculation of interaction forces between blocks is proposed to overcome the limitations of conventional implicit DDA in simulating large-scale problems.
28 citations
TL;DR: An improved potential-based penalty function approach within an explicit three-dimensional (3D) discontinuous deformation analysis (DDA) framework for efficient and robust kinetic analysis of rock block systems is proposed.
25 citations
TL;DR: In this paper, a local in-circle method is proposed to obtain round corners, which eliminates contact indeterminacy and the associated unreasonable sliding behaviors, and the original open-close iteration is modified to enforce stricter convergence criteria of contact analysis.
23 citations
TL;DR: In this paper, a distributed-spring contact model (DSCM) was proposed for the edge-to-edge contact in 2D DDA, which is quite accurate and capable of improving calculation accuracy compared to the O-DDA.
Abstract: Edge-to-edge contact is a fundamental contact type in blocky systems. In two-dimensional discontinuous deformation analysis (2D DDA, and hereinafter DDA for short), an edge-to-edge contact is transformed into two separated vertex-to-edge contacts by applying two pairs of concentrated springs. Although this simplification facilitates the DDA algorithm, it is not always sufficiently accurate and can even yield irregular results. To solve this problem, a distributed-spring contact model (DSCM) that exerts distributed instead of concentrated forces on contact edges is proposed in this paper for the edge-to-edge contact in DDA. Submatrices for the force matrix and stiffness matrix are obtained by minimizing the potential energy of the distributed contact forces and are incorporated into an improved DDA (I-DDA) code. Four examples are evaluated to illustrate the validations and advantages of the I-DDA. The first example is a single square impacting on a base block. Deformation of the contact area is evaluated by comparison with the theoretical deformation solution, and the results calculated by the I-DDA show better agreement with the analytical solution than the original DDA (O-DDA). The second example is an impact validation, proving that the I-DDA is more adaptable to discrete systems containing blocks of different sizes. Then an example and an experiment about block rebounding are provided, demonstrating that the errors in rotation and rebounding exhibited in the O-DDA results are avoided when using the I-DDA, indicating that the I-DDA provides more realistic solutions. The results of this study suggest that the proposed I-DDA incorporating the DSCM is quite accurate and capable of improving calculation accuracy compared to the O-DDA.
22 citations
TL;DR: In this article, the authors extended discontinuous deformation analysis (DDA) to simulate the interactions of twin tunnels in a jointed rock mass and compared the ground subsidence and the rock stress distribution around the tunnels from the DDA simulation are compared to those from the trap-door model.
21 citations
TL;DR: In this article, a reliable numerical simulation of the landslide process contributes to the establishment of evidence-based disaster mitigation measures in seismically active zones, and a simplification of the simulation is presented.
Abstract: The reliable numerical simulation of the landslide process contributes to the establishment of evidence-based disaster mitigation measures in seismically active zones. To achieve this goal, a simpl...
TL;DR: In this article, the authors proposed the last entrance plane (LEP) principle to identify the physical contact plane, which is applicable to resolve contact indeterminacy between convex polyhedral blocks.
TL;DR: Wang et al. as mentioned in this paper analyzed the deformation and instability of the right bank slope of the Dagangshan hydropower station by three-dimensional discontinuous deformation analysis (3D-DDA).
TL;DR: In this article, the authors verified the sub-block DDA method in simulations of continua and showed that the influence of the contact penalty spring stiffness and mesh size on the stress and strain calculations is investigated.
Abstract: Discontinuous deformation analysis (DDA) computes the mechanical behaviours of discrete deformable-block systems. It also has been used to simulate continuous rock fracturing, e.g., through the sub-block approach. In the present study, the sub-block DDA method is first verified in simulations of continua. The influences of the contact penalty spring stiffness and mesh size on the stress and strain calculations are investigated. Thereafter, the fracturing modelling algorithm of the sub-block DDA is improved, which determines the tensile or shear fracturing failure along artificial joints based on the stress state of adjacent sub-blocks according to the maximum tensile stress criterion and the Mohr–Coulomb criterion, respectively. The tensile, shear, mixed-mode, as well as dynamic fracturing failures of rock samples are simulated, and the results are calibrated theoretically or experimentally. Compared with former sub-block DDA fracturing modelling algorithms which determine the fracturing failure along artificial joints based on the contact stresses between sub-blocks, the improved algorithm has better accuracy in terms of the failure strength, and it significantly reduces the influence of the distribution of the pre-set artificial joints on the failure strength and fracturing route simulation results. This work makes DDA a better candidate for use in rock fracturing problem simulations.
TL;DR: This paper develops an efficient disk-based DDA (DDDA) model considering rock-based and liquid-based models for discontinuous deformation analysis (DDA).
Abstract: Simulating large-scale problems are still challenging for discontinuous deformation analysis (DDA). To this end, this paper develops an efficient disk-based DDA (DDDA) model considering th...
TL;DR: A systematic investigation of six iterative methods, namely, symmetric successive over relaxation (SSOR), Jacobi (J), conjugate gradient (CG), and three preconditioned CG methods, for solving equations in three‐dimensional sphere DDA (SDDA), shows that CG is not only the most sensitive to the ill‐condition of the equations but also the most time consuming under both serial and parallel computing.
TL;DR: In this paper, the authors used the spherical harmonic (SH) function to reconstruct the nature sand particle, referred to as SH-body, and derived the discontinuous deformation analysis (DDA) formula based on the principle of minimum potential energy.
TL;DR: In this article, a multi-spring edge-to-edge contact model with Discontinuous Deformation Analysis (DDA) is proposed to evaluate the tensile failure of a joint under asymmetrical tension conditions.
Abstract: Edge-to-edge is the most common form of contact in a two-dimensional joint block system. Discontinuous deformation analysis (DDA) is a powerful tool for handling block systems and treats an edge-to-edge contact as two vertex-to-edge contacts with a couple of normal and shear springs at the extremes of the contact segment. However, this method is unsuitable for evaluating the tensile failure of a joint under asymmetrical tension conditions, even though it can simplify the contact type and increase computational efficiency. This is mainly because the distributed forces at an edge-to-edge contact are simplified as two couples of concentrated forces. To solve this problem, this paper proposes incorporating a multi-spring edge-to-edge contact model with DDA. In the model, several contact pairs with normal and shear springs on an edge-to-edge contact are set to simulate the distributed forces. Several benchmark tests were performed to demonstrate the discrepancy between the original and improved DDAs. The results revealed that the latter more accurately models the stress distribution across the edge-to-edge contact, providing a more reasonable acceleration required to topple a series of blocks resting on an inclined stepped base.
TL;DR: In this article, a semi-analytic geometry iteration (SAGI) algorithm is proposed based on parametric equation of the ellipsoid, which is also extended to cylindrical and conical boundaries.
TL;DR: A full-stage parallelization of 3-D DDA is proposed, in which all the main subroutines that have the potential to be executed in parallel are implemented with parallelization using OpenMP, demonstrating around 5 times enhanced efficiency with 6 threads used.
TL;DR: Discontinuous deformation analysis has gained wide acceptance in geotechnical engineering and is computationally expensive to simulate large-scale engineering problems.
Abstract: Discontinuous deformation analysis (DDA) has gained wide acceptance in geotechnical engineering. The simulation of large-scale engineering problems using DDA is computationally expensive. ...
TL;DR: This study automatically generates a multi-shell cover (MSC) system and develops a novel multi-cover search (MCS) algorithm for 3D cases that expedites contact detection by dividing the geometric elements of polyhedra into several groups, and accelerates contact Detection by efficiently selecting potential contacts using the neighbor relations between faces of polyhedral blocks.
TL;DR: Results indicate that, the proposed algorithm can handle the contact detections of convex polyhedral blocks effectively under critical and complex conditions, which builds a good precondition for the successful development and practical application of the 3D-DDA method.
01 Dec 2020
TL;DR: In this paper, the authors developed a fully coupled hydro-mechanical model for hydraulic fracture network propagation based on the discontinuous deformation analysis (DDA) method, and a new efficient method was proposed to consider the 3D effect in 2D DDA-based fracturing simulations.
Abstract: The Silurian Longmaxi formation in the Sichuan Basin, which is the most important gas-producing shale reservoir in China, is characterized by relatively small effective thickness, large in-situ stress difference and highly-developed natural fracture (NF) system. Microseismic monitoring shows that complex hydraulic fracture (HF) networks with relatively small height could be stimulated in the Longmaxi shale reservoirs. Traditional two-dimensional (2D) numerical models cannot capture the three-dimensional (3D) nature of the limited-height HFs, which is not suitable for investigating the fracturing of Longmaxi shale reservoirs. This work develops a fully coupled hydro-mechanical model for HF network propagation based on the discontinuous deformation analysis (DDA) method. A new efficient method is proposed to consider the 3D effect in 2D DDA-based fracturing simulations. Hence an approximate 3D solution of fracture-induced stress and deformation could be obtained. This method is verified against previous works. Then, a series of simulations is performed to investigate the influence of reservoir thickness, in-situ stress difference and NF pattern on the hydraulic stimulation of Longmaxi shale reservoirs. Modeling results show that limited reservoir thickness is favorable to the formation of HF network. Complex and dense fracture network is easily to be formed in thin reservoirs. Large in-situ stress difference will impede the hydraulic stimulation. However, when the reservoir thickness is small, dense fracture network is still likely to be formed under large stress differences. Besides, the NF system is essential for the formation of HF network. The modeling results indicate that as a result of the limited thickness and highly-developed NF system, complex and dense fracture networks could be stimulated in the Longmaxi shale reservoirs. This work partly accounts for the initial success of gas recovery in the Longmaxi shale reservoirs. It also provides a feasible numerical method and theoretical supports for further optimization of shale gas exploitation in China.
TL;DR: In this article, an angle-based contact detection method was proposed to address the concave contact problem of arbitrary polyhedra, including convex and concave polyhedras, those with cavities and/or holes, and likely their unions.
Abstract: This study presents a novel angle-based contact detection method to address the concave contact problem of arbitrary polyhedra, including convex and concave polyhedra, those with cavities and/or holes, and likely their unions. First, the most important mathematical concept in this study, the angle, is introduced to represent a general polyhedron. Using angles, the topologies of the polyhedra can be far more complex and universal than those previously studied, allowing for the coplanarity of faces and collinearity of edges, and not limiting the polyhedra to simple homeomorphic to closed three-dimensional (3-D) spheres. Second, all the local entrances of two general angles, which are either vertex angle to half-space or crossing edge angle to edge angle entrances, are identified using the entrance formulas. Third, local convex decomposition (LCD) is proposed to decompose any arbitrarily concave angle into a set of convex subangles, making the method easy to implement and naturally compatible with detection of entrance angles. Fourth, the proposed entrance angle method (EAM) is implemented in 3-D discontinuous deformation analysis (DDA) to compute arbitrarily convex/concave contacts. Finally, the EAM-based 3-D DDA method is validated and then employed to investigate the discontinuous mechanical behaviors of complex polyhedral block systems. Overall, the extended 3-D DDA program is sufficiently developed to meet the analysis requirements of complex rock mass projects.
TL;DR: In this paper, a damped contact model based on linear spring-dashpot assumption is adopted and incorporated into 3D DDA to address the energy loss in collisions, and a relationship between viscous damping coefficient and coefficient of restitution (COR) is derived.
TL;DR: In this article, the authors proposed a numerical model based on the discontinuous deformation analysis (DDA) method to study the ballast flight caused by dropping snow/ice blocks in high-speed railways and analyzed the dynamic behavior of ballast particles during their collision with a snow and ice block.
Abstract: Frozen snow/ice blocks drop at high speeds from train causing the ballast to fly up and damage the car body. Thus, in this paper, we propose a numerical model based on the discontinuous deformation analysis (DDA) method to study the ballast flight caused by dropping snow/ice blocks in high-speed railways and to analyze the dynamic behavior of ballast particles during their collision with a snow/ice block. The validation of the proposed model is done by comparing the numerical results with the theoretical and the experimental ones. The numerical results show that the velocity, shape and incident angle of snow/ice block play an important role in the ballast flight. Specifically, the number and the maximum displacement of ballast particles increase as the train speed increases and the incident angle greatly affects the movement direction of ballast particles. The shape of the ice block affects the amount and extent of ballast flight.
TL;DR: When simulating large rotation, the false volume expansion and elastic distortion problems of the block occurs severely in the original discontinuous deformation analysis (DDA), in this article, where the block is assumed to be smooth.
Abstract: When simulating large rotation, the false volume expansion and elastic distortion problems of the block occurs severely in the original discontinuous deformation analysis (DDA). In this st...