ABSTRACT: In order to tackle the problem of rock slope protection, this paper presents some results of rock slope simulation of potential toppling failures of varying degree of discontinuities and of different joint patterns in relation to bolting techniques to be applied to practical slope design for best and effective working function by physical modeling approach by using two-dimensional aluminum block models.
1 INTRODUCTION
When speaking of slope stability problem, most of the time it is referred to sliding mode of failure rather than toppling. But in general, at any construction dealing with slope cut, either sliding or toppling mode of failure will be encountered both directly and indirectly. In spite of this fact, mechanics of toppling in rock mass has received comparatively little research effort owing to the complexities of the problem and the inability to make direct observations in a toppling mass in open mines, dam constructions or road cut slopes. Chappell (1975) studied the numerical simulation of the load distribution of different orientation of joint sets in block model relative to principal applied loads. Ashby (1971), Barton (1971), Hoek& Bray (1974) and many others have also studied toppling slopes in static, physical models. Goodman & Bray (1977) studied limit equilibrium analysis of toppling on a stepped base and developed equations of force and tension in cable to prevent toppling for the stepped base model. Cundall (1974,1977) assumed that rock mass consists of assemblages of discrete blocks and developed a numerical approach to analyze its deformational behavior. Hobst & Zajic (1977) proposed anchoring of a rock face with planes of discontinuity sloping backward. In addition to the above mentioned studies, this paper demonstrates and presents some results obtained from physical model study of the behavior of failure mechanism of toppling in terms of measured displacement traced from block models. It is the authors' intention that the results presented in this paper can be of some guidelines for further physical model study and for practical application to the field problems.
2 MODEL STUDY OF TOPPLING
2.1 Experimental model
Aluminum bars of lxlcm2 and 3x3cm2 in sections, 5cm long, 2.7gm/cm3 were used as main and basic blocks in this study. Model tested is 50cm long (base arm or platform) and 20cm high (at right angle to the base arm) for small model; and 150cm long, 100cm high for large model. To increase the size of aluminum bar for diversified point patterns and different discontinuities, lxlx5cm3 blocks were attached together by using cellophane tape to produce aluminum bars of lx2x5. lx3x5, lx4x5cm3 blocks for small scale model; and 3x6x5, 3x12x5cm3 blocks for large model. Two kinds of physical models were used, one was with a fixed sup- porting arm made of U-shaped steel rod welded at right angle to the platform for stacking up aluminum bars (see Fig.1). The platform itself is hinged to the main steel framework and rotatable for the purpose of simulating varying 3oint inclinations. The other was similar to the former one except that the supporting arm was hinged to the platform and, therefore, rotatable in order to control the initial movement of potential toppling model (see Fig.2).
