Natural slopes can be classified by referring to the activity state (Varnes, 1978). Active slopes are those that are either currently moving or not moving at the present but have moved within the last seasonal cycle. Inactive slopes are those where there is no evidence that movement has taken place within the last seasonal cycle. These slopes may be dormant, when the failure causes are still present and a movement may occur again. or they may be stabilized when the factors causing the movement have been removed naturally or by human activity. Zaruba & Mencl ( 1969) and Varnes ( 1978) subdivided slope movements according to age. A slope movement is called 'recent' when it has occurred in recent decades in a slope which has not yet been the center of mass movements. A movement for which there is no memory or historical records is called ancient. A fossil movement, finally, is where a slope movement occurred in a previous geological age. The causes which determine sliding movement in a slope depend on phenomena which contribute to a shear stress increase and/or to a reduction of shear strength. The principal phenomena which contribute to a shear stress increase involve the toe or the slope surface weakening or the slope surcharging. The toe or the slope surface weakening can be due to:
1. Erosion by streams, rivers, glaciers, waves, tidal currents, sub-aerial weath ering, wetting and drying and frost action;
2. Subsidence, previous rock fall, toppling, sliding and superficial scaling;
3. Phenomena connected to human activity such as mining or civil excavations, channel construction or water level variation in the toe zone of reservoirs. Surcharges can also be induced by natural causes or human activity. Natural surcharges are due to rain water or snow weight, or to water percolation in rock discontinuities. Surcharges due to human work are embankments, mining

Tidak tersedia versi lain

Tidak Ada Data