Discontinuous Deformation Analysis Model Research Articles

Numerical simulation of full desiccation process of clayey soils using an extended DDA model with soil suction consideration

Soil desiccation is a common physical phenomenon, which causes many geotechnical problems to unsaturated clayey soils. In this paper, a proposed model was incorporated into the original Discontinuous Deformation Analysis (DDA) to simulate the full desiccation process of a clayey soil from volume shrinkage to desiccation cracking and then to desiccation curling by focusing on soil suction. In this model, evaporation-induced soil volume shrinkage and suction-induced tensile failure were separately considered, in particular, soil suction was reasonably treated as an equivalent attractive force rather than a strength parameter. Then, a constrained desiccation test was simulated using the extended DDA model, and obtained numerical results were compared with the experimental results. The comparison results show that this model can capture the main features of the full desiccation process of the clayey soil. Moreover, the influences of soil suction and sample thickness on the desiccation cracking and curling were investigated, which agrees with the laboratory observations. This work aims to propose a novel yet simple model to reproduce the key characteristics of the soil’s full desiccation process, and the results demonstrate that the extended DDA model can be served as a promising approach to analyzing the full desiccation process of clayey soils.

Dynamic process analysis of the Niumiangou landslide triggered by the Wenchuan earthquake using the finite difference method and a modified discontinuous deformation analysis

The Niumiangou landslide was the largest landslide triggered by the 2008 Wenchuan earthquake, which was significantly affected by the amplification effect of seismic acceleration. The ring-shear experiments indicated that the materials in the source area of the Niumiangou landslide were subjected to friction degradation under a big shear displacement, which may result in rapid movement of the landslide. In order to better understand the landslide movement and study the effect of the friction degradation on movement mechanisms, the dynamic process of Niumiangou landslide was simulated with a new numerical method, which combines the finite difference method (FDM) and the discontinuous deformation analysis (DDA). First, the FDM was used to study the initiation time, amplification effect and velocity of the landslide. Afterwards, these initiation velocities were applied to the blocks in the DDA model by corresponding coordination in the FDM model. A displacement-dependent friction model of the sliding surface was incorporated into DDA code to further understand the kinetic behavior of the landslide. The results show that the displacement-dependent friction strongly decreases the friction coefficient of sliding surface under a big displacement, which can obviously promote the run-out and velocity of landslide. The model output well matches the topographic map formed by the landslide. This implies that the proposed model can be applied to the simulation of earthquake-induced landslides with amplification effect, and the friction degradation model is important to clarify the movement mechanism of high-speed and long-distance landslides.

Quantitative Analysis of Seismic Response of Rock Slopes Using Discontinuous Deformation Analysis — A Case Study

For the prevention and mitigation of hazards, it is crucial to quantitatively analyze the seismic response of rock slopes. However, only a few studies have quantitatively analyzed the seismic response of rock slopes; these studies have considered topographic effects only and have neglected geological site effects, such as impedance contrasts and fractures, which are important factors affecting the seismic response of rock slopes, as revealed by multiple recent phenomena. Therefore, this study primarily aims to investigate the possibility of employing a numerical model for quantitatively analyzing the seismic response of rock slopes by considering the geological site effects. Herein, a discrete element method, i.e., discontinuous deformation analysis (DDA), was employed for the dynamic analyses, and a well-monitored rock slope, Mount Dong, was selected as the case study. In the proposed DDA model, horizontal and vertical ground motions were applied simultaneously. The different weathering degrees of the Mount Dong rock layers were considered to reflect the impedance contrasts, and the penalty value at the fractures was altered according to the stiffness for reflecting the fracture effects. Furthermore, a set of optimal boundary settings, especially for DDA, were applied to handle seismic dynamic problems. Results show that DDA can quantitatively reflect the seismic response of Mount Dong along a single direction, such as the horizontal direction, which is sufficient to satisfy engineering requirements. The peak ground acceleration amplification analyses indicate that: 1) a strong impedance contrast is more important than topographic effects for the seismic response of Mount Dong; and 2) in addition to the impedance of rock layers, widely spread fractures also play an important role in contributing to the seismic response anisotropy of rock slopes. Finally, spectral amplification analyses reveal that the responses of the inner and surface portion of Mount Dong are significant in a low- and high-frequency range, respectively.

An Efficient Disk-Based Discontinuous Deformation Analysis Model for Simulating Large-Scale Problems

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...

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

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.

A new DDA model for kinematic analyses of rockslides on complex 3-D terrain

Landslides are common phenomena in mountainous regions worldwide. Over the past two decades, catastrophic rockslides in mountainous regions have caused serious damage and fatalities. To develop effective preventive countermeasures, it is important to estimate the kinematic behavior of displaced masses after slope failures, such as the velocity, run-out distance, and extent. Discontinuous deformation analysis (DDA) is an appropriate tool to analyze the dynamics, kinematics, and deformability of a block assembly. Many studies have reported applications of DDA to kinematic analyses of rockslides on two-dimensional (2-D) terrain. However, because of the restrictions of numerical techniques, few kinematic analyses of rockslides on three-dimensional (3-D) terrain have been performed using DDA. This study developed a new DDA model for the analysis of rockslides on 3-D terrain. First, contact treatment techniques for the 3-D model were developed to create an accurate and efficient computational scheme. The new model was then verified by the benchmark tests on the four basic types of block motion on 3-D terrain. Finally, the new model was applied to a designed rockslide with complex terrain to demonstrate its practical applicability. The results indicate that the new 3-D DDA model is an effective tool to analyze 3-D rockslides and could potentially be used to optimize protection designs for rockslides.

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

AbstractThe 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...

Application of the discontinuous deformation analysis method to stress wave propagation through a one-dimensional rock mass

The analysis of stress wave propagation through a rock mass is an important issue in rock engineering, and the discontinuous deformation analysis (DDA) method provides an effective tool to solve this problem. In this paper, based on the motion equations of block system with the Newmark integration method, the DDA method improved by the viscous boundary and the force input method is employed, and some investigations are made to extend the capability of the DDA method to address the wave propagation problem. First, for providing a quantitative method to control the damping of the DDA method, the computing methods of the damping ratio for both viscous damping and numerical damping are presented, which can effectively simulate the energy dissipation of stress wave propagation. Second, based on the one-dimensional DDA model, a further study on the size choice of a sub block for stress wave propagation is developed, which considers the homogeneous rock and the joint rock mass, and suggested values of block element ratio for both P-wave incidence and S-wave incidence are obtained by comparing with the theoretical solutions. Last, abilities of the DDA method to simulate both the no tension and slipping characteristics of a joint are validated, and the effects of the joint on wave propagation are also investigated.

An improved three-dimensional spherical DDA model for simulating rock failure

In this paper, a discontinuous numerical model, namely SDDARF 3D (three-dimensional spherical discontinuous deformation analysis for rock failure), is proposed for simulating the whole process of rock failure. Firstly, within the framework of the classical discontinuous deformation analysis (DDA) method, the formulation of three-dimensional spherical DDA (3D SDDA) is deduced; secondly, a bonding and cracking algorithm is constructed and the SDDARF 3D model is proposed; thirdly, corre- sponding VC++ calculation code is developed and some verification examples are calculated. The simulated results can intuitively reproduce the failure phenomena of rock mass, indicating that the proposed SDDARF 3D numerical model is correct and effective.

Particle crushing simulations with improved discontinuous deformation analysis

Purpose – Rock-fill dams are embankments of compacted free-draining granular earth containing an impervious zone. Earth utilized in such dams often contains a high percentage of large particles – hence the term rock-fill. Mass stability of these dams results from friction and particle interactions rather than through a cementing agent binding the particles together. However, high-stress conditions and prolonged exposure to the elements can severely damage rock-fill. Therefore, understanding and modeling rock-fill breakage is important for dam engineering. The purpose of this paper is to improve discontinuous deformation analysis (DDA) techniques for modeling rock-fill breakage, proving the new method using simulations of spherical particle crushing. Design/methodology/approach – This work models rock-fill as bonded ellipsoid particles, and develops an improved DDA method to model the breakage of particle assemblies. The paper starts by describing the principles of three-dimensional DDA for spherical particles, and then derives the submatrices for normal contact, shear contact, and frictional force. The new algorithm incorporates a bond model with a revised open-close iteration algorithm into the DDA method to simulate particle crushing. To validate the improved DDA method, calculated particle contacts and movements are validated against theoretical results. Finally, this work performs a series of point-loading experimental tests for cement ellipsoid particles of both high and low compression strengths, with the test results compared against the results from corresponding DDA simulations. Findings – In particle crushing tests, the force and displacement show an approximately linear relationship until the crushing point, at which point low compression ellipsoid particles split into several large pieces while the high-compression particles break into many small fragments. The DDA simulation results are in good agreement with the crushing tests, demonstrating the validity of the DDA method for solving particle crushing problems. Although the improved DDA model is applicable to rock-fill particle crushing studies, some issues remain, particularly in increasing calculation efficiency and performing large-scale computations and long real-time simulations. Future research should address these issues. Originality/value – A bond model with a revised open-close iteration algorithm is incorporated into the DDA method. The simulated results shed insight into rock-fill crushing mechanisms, an element of concern in engineering practices.

Safety evaluation of an ancient masonry seawall structure with modified DDA method

Abstract The ancient masonry seawall along China’s Qiantang River is an important structure for defending the prosperous estuarine area, including Hangzhou, Jiaxing, and part of Shanghai, against violent floods, tides and waves. Modified discontinuous deformation analysis (DDA) is used here to analyze the failure mechanisms and stability of the blocky seawall structure. The backfilling soil is properly integrated into the DDA model, by means of the proposed soil discretization approach, and with an accurate interface shear strength model that the authors presented. According to the simulation results by the modified DDA, the existing seawall is generally in good state. Nevertheless, routine inspection and early restoration are recommended to avoid progressive failures of the seawall.

A numerical study on the effect of shear resistance on the landslide by Discontinuous Deformation Analysis (DDA)

Japan is located in Circum-Pacific earthquake zone, which is one of the most seismologically active areas in the world. As a result, landslides have occurred frequently and often cause serious damage not only to human lives but also to the various important structures such as national roads, railway, electric power plans etc. From the engineering point of view, to investigate the mechanism of landslide due to earthquakes and estimate the damage caused by landslides are important issues. In this study, as the first step, to check the validity of DDA simulation for the seismic problems, a series of shaking table tests were carried out in the laboratory and simulated by DDA. Then, one of the largest landslides occurred in Aratozawa Area, Miyagi, Japan in 2008 caused by Iwate-Miyagi Nairiku Earthquake was simulated using DDA and discussed the mechanisms of the landslide. The 2-D DDA model for one of the survey lines was created based on the geological survey, and physical properties were determined from the laboratory tests using rock/soil samples obtained from the landslide site. In this study, to discuss the mechanism of the landslide, a series of parametric study in terms of shear resistance along the fractures was conducted.

Failure mode analysis of jointed rock masses around underground opening under excavation unloading

The failure modes and loosened mechanism for jointed rock masses around an underground opening under excavation unloading are studied using the discontinuous deformation analysis (DDA) method. A sequential excavation algorithm for jointed rock masses is proposed and implemented into the original DDA program. Different combinations of joint dip angle are used to study their effects on the failure modes and deformation behaviour of jointed rock masses. The results of both DDA and physical model show that the failure modes of jointed rock masses around the underground opening are mainly dependent on disadvantage combination of free excavating surface and discontinuities surfaces. The different joint orientations result in different failure modes and collapse areas of surrounding rocks. Opening and sliding failure in the left and right sidewalls of the underground opening occur for the orthogonal joint set with dip angles of 30×120°, while toppling failure was observed in the right sidewall for the joint set with dip angles of 45×135°.

Computational framework for discontinuous modelling of masonry arch bridges

An investigation into using continuum/discontinuum based techniques to analyse backfilled masonry arch bridges is presented. Three different computational modelling tools, discontinuous deformation analysis (DDA), discrete element based analysis using particle flow code and the non-linear finite element analysis using diana have been utilised for this purpose and comparison are made with an experimental model developed at Edinburgh University. Load dispersal through the backfill in the DDA model is improved by using Voronoi tessellation based techniques and the displacement control loading have been utilised in all cases to trace the structural response beyond the collapse load and to identify the collapse mechanisms. The capability and limitations of the methods are demonstrated and some sensitivity analyses are also presented for the semi-circular arch model.

Aseismio fault slip and block deformation in North China

In North China, the tectonic fault-block system enables us to use the Discontinuous Deformation Analysis (DDA) method to simulate the long-term cross-fault survey and other geodetic data related to aseismic tectonic deformation. By the simulation we have found that: (1) Slips on faults with different orientation are generally in agreement with the ENE-WSW tectonic stress field, but the slip pattern of faulting can vary from nearly orthogonal, to pure shear along the strike of the faults, this pattern cannot be explained by simple geometric relation between the strike of the fault and the direction of the tectonic shortening. This phenomenon has been observed at many sites of cross-fault geodetic surveys, and might be caused by the interactions between different blocks and faults. (2) According to the DDA model, if the average aseismic slip rate along major active faults is at the order of several tenths of millimeter per year as observed by the cross-fault geodetic surveys, the typical strain rate inside a block is at the order of 10−8 year−1 or less, so that the rate of 10−6 year−1, as reported by observations in smaller areas, cannot be the representative deformation rate in this region. (3) Between the slips caused by regional compression and block rotation, there is a possibility that the sense of slip caused by rigid body rotation in two adjacent blocks is opposite to the slip caused by the tectonic compression. But the magnitude of slip resulting from the tectonic compression is much larger than that due to the block rotation. Thus, in general, the slip pattern on faults as a whole agrees with the sense of tectonic compression in this region. That is to say, the slip caused by regional compression dominates the entire slip budget. (4) Based on (3), some observed slips in contradiction to ENE tectonic stress field may be caused by more localized sources, and have no tectonic significance.