INTRODUCTION

In the accident at the slope, it is most difficult to foretell a generation of rock-collapse. The method to evaluate the danger is synthetically judged by the form of topography, geology, groundwater, meteorology, and vegetation, connecting with a factor and a inducement of the generation of rock-collapse. But this evaluation is qualitative and several problems lie in the base of the estimation.

Rock-collapse can be classified into the following two types by the factor or the form of motion at a generation point. One type is that a rock block floats. out from it's matrix and then falls down. The other type is that a boulder flakes off from the crack of it's basic rock and then fall down. The danger of generating rock-collapse differs by the stick between a rock block and it's matrix or that of the cracks composed a boulder. The tremor property of seismic amplitude, acceleration, frequency which propagate under the rock block or the boulder differs by the difference of the stick. Therefore it is considered that the evaluating the danger of rock-collapse enables by making the seismic property of the rock locks and boulders clear and in the methods Which show the danger of generating rock- collapse qualitatively, the seismic exploration is useful.

Referring to the evaluation of rock-collapse by vibration. various experiments were Performed at the Laboratory of Japan Highway Public Corporation. This thesis is described about the relation between the stability and the Vibration property of the rock block or boulder and evaluating the danger of rock-collapse, based on this experimental results.

EXAMINATION

The factors connecting with the stability of a rock block or a boulder on the slope are that the stick between a rock block and it's matrix or of the crack is the most one, but besiding that it can be considered the inclination angle of the slope, the shape and size of a rock block or boulder, and the contacted form or the environment of that. In this experiment, as these factors were changed, every point of vibration of a rock block, boulder and the basic rock of the slope were measured and then the vibration property was investigated.

A lot of rock block were necessary. For these shapes and sizes to be changed variously, rock blocks were made of mortar and set on the artificial shape and then the natural tremor and the impulse vibration were measured. It was difficult for a boulder to be made as a model, so a boulder that was on the natural slope was seiected and the vibration was measured.

Examination of rock blocks on the slope

As in Fig. 1, the artificial slope was made of cement-mortar on the horizontal ground and covered with loam and hardened by a shovel. On the artificial slope the rock block model made of mortar was set in the loam and experimented.

Nature and situation of the slope and rock block

"Inclination angle of the slope" As it was considered that the stability was changed

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