Abstract
A laser displacement measurement and AE monitoring were employed to monitor an unstable rock mass left after rock block failure, to secure repair works under it. Accumulated displacements around 50mm were measured for 20 days. However, since neither rapid increase of the displacements nor active AE occurrence was observed, it was considered that the rock mass was stable and a failure would not occur soon. The fact that the rock mass did not failed down in spite of such a large displacement of 50mm suggests that various kinds of displacement measuring techniques having not so high accuracy are applicable if continuous measurements are conduced. The results also indicate that AE data are very helpful to judge risk of rock mass failure.
