Showing papers on "Discontinuous Deformation Analysis published in 2006"

Review of validation of the discontinuous deformation analysis (DDA) method

Abstract: Over the last decade, researchers in the discontinuous deformation analysis (DDA) community have dedicated a great deal of effort to document the accuracy of the method by performing validation studies. This paper contains a summary of more than 100 published and unpublished validation studies which comprise the body of DDA validation information to which the authors have access. The studies are grouped into three general categories: (a) validation with respect to analytical solutions, (b) validation with respect to results of other numerical techniques, and (c) validation with respect to laboratory and field data. Three general techniques for validation are described: qualitative assessment visually examining runtime behaviour of simulations, semi-quantitative assessment comparing numerical results of simulations, and quantitative where numerical simulation results are evaluated in detail with respect to similar analytical, laboratory or field results. We find that for many of the problems addressed by the papers in this review, DDA performs more than adequately for engineering analysis. Copyright © 2006 John Wiley & Sons, Ltd.

Producing joint polygons,cutting joint blocks and finding key blocks for general free surfaces

Abstract: This paper describes a process of cutting blocks from statistically generated finite joint polygons in 3D space.If the ratio of joint length divided by joint spacing is less than 10,the rock mass is likely connected.If this joint length ratio is greater than 10,the rock is likely to be blocky.An algorithm is also presented for finding all removable blocks along any given moving direction.The rock mass boundary can be any excavated and natural free surfaces.The algorithm works for both joint sets and for any joint system where each joint has its own direction.This is an application of polygon cutting code DC of 3D DDA.

Discontinuous deformation analysis with second-order finite element meshed block

Abstract: The discontinuous deformation analysis (DDA) with second-order displacement functions was derived based on six-node triangular mesh in order to satisfy the requirement for the accurate calculations in practical applications. The matrices of equilibrium equations for the second-order DDA were given in detail for program coding. By close comparison with widely used finite element method and closed form solutions, the advantages of the modified DDA were illustrated. The program coding was carried out in C++ environment and the new code applied to three examples with known analytical solutions. A very good agreement was achieved between the analytical and numerical results produced by the modified DDA code. Copyright © 2006 John Wiley & Sons, Ltd.

Static and dynamic stability analysis using 3D-DDA with incision body scheme

Abstract: Discontinuous deformation analysis (DDA) provides a powerful numerical tool for the analysis of discontinuous media. This method has been widely applied to the 2D analysis of discontinuous deformation. However, it is hindered from analyzing 3D rock engineering problems mainly due to the lack of reliable 3D contact detection algorithms for polyhedra. Contact detection is a key in 3-D DDA analysis. The limitations and advantages of existing contact detection schemes are discussed in this paper, and a new approach, called the incision body (IB), is proposed, taking into account the advantages of the existing methods. A computer code 3DIB, which uses the IB scheme as a 3D contact detection algorithm, was programmed with Visual C++. Static and dynamic stability analysis for three realistic engineering problems has been carried out. Furthermore, the focus is on studying the stability of a gravity dam on jointed rock foundation and dynamic stability of a fractured gravity dam subject to earthquake shaking. The simulation results show that the program 3DIB and incision body scheme are capable of detecting 3D block contacts correctly and hence simulating the open-close and slide process of jointed block masses. In addition, the code 3DIB could provide an effective tool for evaluating the safety of 3D dam structures, which is quite important for engineering problems.

Researches on deformation and failure characteristics of an underground powerhouse with complicated geological conditions by dda method

Abstract: As a numerical modeling approach,discontinuous deformation analysis(DDA) method was employed to analyze effects of different factors on the deformation characteristics of an underground powerhouseThe effect factors mainly consist of stress lever coefficient,rock reinforcement,joint structure pattern and strength properties of joints in surroundings,etcIt has been shown that DDA model can get reasonable results with different simulation casesThe deformation of surrounding rock mass is closely relevant with rock stress conditions assumed beforehandAs the surrounding rock mass has the characteristics of hard and soft rocks being formed alternatively,where the multi-layer of shear zones exists between them,the displacements of sidewall have larger increasing intervals compared with those of roof arch displacements of the powerhouse when horizontal stress increases;and the discontinuous sliding along surfaces of shear zones will occur normallyReinforcement with rock bolts will bring favorable effects on rock surroundings in controlling deformation and stress distribution propertiesIf a series of key blocks collapse,the joint intersections in surrounding rock mass,in some cases,will exert negative effects on the stability of powerhouseOn the other hand,for joint intersections being under stable state,unstable deformations of rock surroundings will occur when the joint strength is reduced to some extentThis paper presents some relevant results with DDA method,and some problems associated with DDA have been discussed

Numerical simulation of startup and whole failure process of qianjiangping landslide using discontinuous deformation analysis method

Abstract: On July 13,2003,a foundation rock landslide with total volume of about 204×107 m3 happened in Qianjiangping on the left bank of Qinggan River in Zigui County located in the Three Gorges Reservoir areaIntensive attention has been aroused for the geologic features and startup mechanism of the landslide because it located in the Three Gorges Reservoir area and happened in the time no more than 2 weeks after the storage of the Three Gorges Reservoir up to 135 m elevationOn the basis of field investigation on the general geological conditions and its mechanical parameters of the actual landslide,and with advantages of real time variable employment and large discontinuous deformation simulation in the method of discontinuous deformation analysis(DDA),the startup criterion for a landslide using DDA numerical modeling has been studied;and the numerical simulation of the startup and whole failure process of the landslide has been carried out by use of DDA methodIt is shown that the main reason of Qianjiangping landslide is the reduction of mechanical parameters of controlled sliding surfaces in the landslide body resulted from rainfall and rise of reservoir water levelThe landslide belongs to thrust load caused landslideCompared to the actual process characteristics of the Qiangjiangping landslide,the maximum landslide velocity,and the maximum slide distance are quite reasonable and acceptableThe total duration of the landslide obtained by DDA modelling is about 40 sIn addition,the methods adopted in this paper supply a new approach for stability study of landslide or other geotechnical engineering

Analysis and improvement of scheme to detect contacts in system composed of 3d convex polyhedral blocks

Abstract: Discontinuous deformation analysis(DDA) and discrete element method(DEM) are two important numerical methods that analyze large-scale opening,sliding,and complete detachment of elements or blocks of discontinuous media such as fractured blocky rock masses.These methods have been widely used in codes and applied to two-dimensional analysis of discontinuous deformation.However,the methods have scarcely ever been applied to three-dimensional analysis of practical rock engineering problems.Until recently,spheres,bonded spheres and ellipsoids are used as elements or blocks in 3D codes,but they can not reveal the real behavior of more angular block system such as fractured rock masses in which joints,fissures and faults are intersected.During modeling the 3D rock block system,DDA and DEM confront a great difficulty in contact detecting between two blocks because the existing detection methods cannot get the exact contact relationship sometimes between two 3D blocks that contact each other.The common-plane(C-P) method introduced by Cundall can detect the correct contact relationship between two 3D blocks provided that the common-plane position could be located correctly. Unfortunately,the algorithm to position the common-plane can't always get the correct position because it can't reveal exactly the influence of variation of a block geometrical shape upon the common-plane position.The limitations and advantages of three contact detection schemes,especially two main schemes used in codes,are discussed.The principle only according to which the correct detection method can be brought out is represented. Based on advantages of the existing methods,a new approach called incision body is put forward.The simulation examples of block movement are also given.The simulation result shows that the incision body method is capable of overcoming indeed limitations of the existing methods,detecting 3D block contacts correctly and hence simulating the interactive detachment and sliding between two blocks.

Coupling method of three-dimensional DDA-FEM and its application

Abstract: A numerical model that coupled three dimensional discontinuous deformation analysis(3D DDA) with finite element method was presented.The displacement field and the stress field were solved by proper internal discretization of deformable blocks using finite element meshes.The contacts between the deformable blocks were modelled with DDA method.Based on the variational principle of minimum potential energy,the global equilibrium equations of the coupling method was established.The contact matrix and friction force matrix were derived and added to the global equations.The problem of interaction of the concrete foundation and the elastic base was analyzed to illustrate the application of the proposed method.The numerical results demonstrated the validity and the advantages of the coupling method.

Application of elasto-viscoplastic block element method to stability analysis of right abutment slope in Longtan Hydropower Project

Abstract: The principle of 3D elasto-viscoplastic block element method is introduced.This method exclusively takes deformation and strength property of the discontinuities into consideration,with the assumption that the rock blocks are rigid.The governing equation is deduced on the base of the equilibrium equation of block system,the compatible equation of displacement between the discontinuities and blocks and the elasto-viscoplastic constitutive equation of discontinuities.In right abutment slope of Longtan Hydropower Station,the geology is complicated,and the stability of blocks is a serious question.The 3D elasto-viscoplastic block element method is adopted to analyse the stability of the given blocks limited by the typical discontinuities,a series of safety factors of strength reservation under various work conditions are obtained.In the same time,the sensitivity analysis is performed aimed at such important factors influencing the stability of blocks as geometrical and mechanical parameters of discontinuities to provide proposals for engineering design.The application indicates that,as a new numerical method for hydraulic engineering,the elasto-viscoplastic block element method has the merits of validity,practicability and convenience for the stability and deformation analysis of block slope with complicated geology.

Mixed Discontinuous Finite Element Methods for Multiphase Flow in Porous Media

Abstract: In this paper we present an application of mixed discontinuous finite element methods to the simulation of two phase immiscible flow in porous media. The partial differential system describing this flow is written in terms of an elliptic equation for a global pressure and a parabolic equation for a saturation. Both of these two equations are solved using the mixed discontinuous finite element methods. Numerical results are presented for P0, P1, and P2 discontinuous elements. The P0 results are very close to those generated by the standard finite difference method, while the P1 and P2 results seem more accurate.

Progress of seismic theoretical analysis for high arch dams

Abstract: Based on the anti-seismic standards and stability evaluation criteria of high arch dams,the current calculation methods for high arch dams are systematically summarized,which include the rigid body limit equilibrium method,method combing rigid body limit equilibrium and finite element,discontinuous deformation analysis method(DDA),numerical manifold method,interface element method,FE-BE-IBE coupled method,stochastic finite element method,artificial transmitting boundary and explicit FEM,parallel computation and modeling test.Advantages and disadvantages of each method are also presented.