ABSTRACT:

The discontinuous deformation analysis combined with the artificial joints was used to examine the effects of various factors on the deformability of a block-in-matrix mass. DDA computation results indicate that although the block volumetric proportion plays the major role, other factors like block geometry (shape, orientation and size), block arrangement, deformability contrast of block to matrix, and interface strength may become dominant in a certain situation. The intention of using DDA as a design tool in problems of block-in-matrix materials is also emphasized.

INTRODUCTION

In nature, there are a tremendous number of geomaterials (rock or soil) with a texture of block-inmatrix, abbreviated as him by Medley (1994). Materials of this kind universally have isolated interior blocks (shaded areas) embedded in a matrix (blank area), as depicted in Figure la. The physical and mechanical properties of the matrix and interior blocks may not be the same; in most cases the matrix is weaker and softer than interior blocks. The interfaces between the matrix and interior blocks as well as other fractures are inherent discontinuities with limited strength. Block-inmatrix rocks (himrocks) include melange, breccia, conglomerate, and tillite. Analogous soils like till, talus and gravel formations are bimsoils.

When working with these widespread bimrocks or bimsoils, a formidable yet crucial engineering practice is to determine their representative mechanical properties for design. Using those of the weaker matrix has been proven over-conservative. Extensive laboratory testing of physical model melanges (Lindquist and Goodman, 1994) showed the increasing trend between the strength and the volumetric proportion of blocks Pv. Medley (1994) then proposed a graphic model to determine the Pv of in-situ bimrocks. However, considering a him mass composed of the matrix, blocks and interfaces, the true relationship may not be so simple and Dedicated to Prof. R. E. Goodman for endless couragement. straight-forward. Therefore, the author suggests the combination of the following factors, which affects the mechanical properties of bim materials:

a) the block proportion in volume, Pv;

b) the shape and orientation of blocks;

e) the arrangement of blocks;

d) the size and size distribution of blocks;

e) the property contrast of block to matrix;

f) the strength of interfaces;

where Factors a) d) mainly relate to blocks, Factor d) also connects with the interface length per unit volume given a Pv, Factor e) indicates the difference in properties of the matrix and blocks, and Factor f) depicts the binding strength between them.

In order to evaluate the relative significance of these factors, one economically feasible way is using numerical simulation. Considering the discontinuous nature of interfaces between the matrix and blocks, the numerical simulation requires a discontinuous model. Among several discontinuous methods, the Discontinuous Deformation Analysis (DDA) pioneered by Shi and Goodman (1990) was selected for this study, because of its rigorous mathematical soundness, strict equilibrium satisfaction and robust contact scheme. The current code of DDA is limited to two-dimensional problems yet.

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