三维块体接触判断方法的分析与改进

非连续变形分析方法和离散单元法都是可以计算非连续介质大位移问题的数值方法，目前在二维问题的计算中应用较多，但在工程实际问题的计算中还未能得到广泛应用，因为实际的工程问题如岩体结构都是三维问题。而在计算三维问题时存在一个困难，就是难以快速、准确地判断块体之间的接触类型。对已有的3种接触判断方法尤其是其中已用于实际计算的公共面法、侵入边法进行分析，指出各种方法在进行接触判断时存在的问题。同时在综合已有方法优点的基础上，给出建立正确接触判断方法的原则并提出切割体法。2个算例的计算结果表明，该方法的确有效地解决了已有方法存在的问题，能够正确判断三维块体之间的接触关系，从而模拟块体之间的错动滑移过程。

ANALYSIS AND IMPROVEMENT OF SCHEME TO DETECT CONTACTS IN SYSTEM COMPOSED OF 3D CONVEX POLYHEDRAL BLOCKS

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.