Permanent rock slope is gradually becoming taller at many limestone mines in Japan. Steep slope height now comes to 200mover. The height makes to 500min future. Study on the slope stability continues with monitoring and numerical analysis. This is a numerical study used by an eigenvalue problem. Eigenvalue analysis can show the dynamic characteristic about rock slope. Natural frequency and the deformation mode depend on the structure of rock slope. This paper shows the dynamic characteristics of simple rock slope, cover rock type rock and slope damaged on surface. Natural frequency comes down with progress of damage on slope surface. Deformation mode of cover rock type slope generates tensile stress at a boundary of cover rock in lower frequency mode. And, there are many local movements on slope in higher frequency mode.
There is the characteristic called the natural vibration in all structures and solids. The structure itself moves and an external force acts on it, so vibration occurs in many cases. The vibration by the wind and earthquake of a building is an important subject at the design (Chopra, 2001). It is important to determine natural frequency and natural vibration mode when calculating the response characteristic of a structure. Of course natural vibration characteristic exists also in a rock slope (Hirata, 2006). A natural vibration characteristic is expressed with eigenvalue and eigenvector. Eigenvalue and its eigenvector can showthe dynamic characteristic about rock slope. Natural frequency and deformation mode determined by eigenvector depend on the structure of slope. Especially, natural frequency in higher mode is sensitive to change of slope structure, such as damage by blasting, generations of plastic zone by stress concentration or weathering. On the contrary, lower natural frequency is insensitively even if the slope height defers 100m (Inokuchi, 2006). In consequence, it is expected that a monitoring of dynamic characteristic on the slope detect the slight variation in the local position. So, wewant to know what the dynamic responses are in many type of rock slope.
The rock slope containing a base part shows elasticity, and is modeled with a triangle shaped finite element.
Our first object is to know the dynamic characteristic of rock slope in the sound condition. Next, it reduces elastic moduli of surface rock affected by blasting, creep and so on. In a limestone mine, there are many cases where a weathering rock is behind permanent rock slope after excavation. A base rock is 400m in the depth and 1000m in the width. There is a slope on the base rock. The angle of inclination of a slope is 50 degrees. Slope height is set to 400 m. Both sides and lower end that are surrounded by point A, B, C and D in Figure 1 are fixed. And, the level surfaces and the slope between point A and F, between point D and E, and between point E and F are free.
