ABSTRACT:

This paper describes the motion of rotations of the body in the deformation mode, caused by the discontinuous planes, near the excavating rock surface, by using the finite deformation theory, while considering the rigid body rotations by Jaumann derivative.

The simulated numerical results are essentially as follows: The rigid body rotation deformation mode is expressed as toppling of blocks, and the cause there of. Also the plastic region is concentrated around the excavated surface of the rock masses,caused by normal stress of the joint element (model of the seams and joints), compared to small deformation theory.

1. INTRODUCTION

The deformation characteristics of excavating surfaces In rock masses during the construction of slopes, tunnels and underground powerhouse caverns, depends on the discontinuous planes, such as seams and joints, existing in it.

In order to analyze the joint behavior, some numerical models are proposed as OEM (Distinct Element Method, Candull, 1974), RBSM (Rigid Body Spring Method, Kawai,.1977), and a lot of research shows the simulation of collapse by slip line analysis, in the slope stability failure mode by using it. However, those theories neglect the elastic deformation of blocks, and sometimes their results are influenced by Its numerical modeling.

On the other hand, Goodman (1968) proposed by Finite Element Method with the Joint element in the small deformation theory, which neglects the rigid body rotation mode of the body.

Therefore, these models did 'not express the deformation mode of both slip and rotation of the body, which occurred precisey on the discontinuous planes of each block.

This paper examines the applicability of the finite deformation theory of kinematic motion, using the equation presented by Lubaluda and Lee (1981), for finite element models, with the joint element of the above rock structures.

The open cut ditch and underground powerhouse cavern models, which have discontinuous planes near the excavated surface of the rock masses, are analyzed by using it.

2. CLASSIFICATIONOF FINITEDEFORMATIONTHEORY

The mechanics of structures, using the theoretical pure kinematic motion of body for a lot of on going research, are classified by Kleiber et al (1982) as follows.

• A: small rotations - small strains

• B: large rotations - small strains

• C': small rotations - large strains

• C": large rotations -large strains

The A group is the small deformation theory (classic theory), B is well-known as the buckling analysis for the plate and shells. C' and C" are categorized as the finite strain problems, such as the plastic metal forming roblem, etc., and a lot of research has been presented in the past few years (Kitagawa et al, 1980).

If we consider the deformation behaviour of the geotechnical foundation, in physical problems, when constructing embankments and trenches under condition of soft clay model, it corresponds to group C". In the case of hard rock with discontinuous planes, as in the seam and joint models, the mode of deformation depends on the motion of each block, such as mentioned above, the rotation of body and the amount of slippage between discontinuous planes, are classified as category B.

This content is only available via PDF.