STABILITY ANALYSIS OF PALEO-SLIDED RED BEDROCK MASS AT POWERHOUSE SITE OF WAWU MOUNTAIN HYDROPOWER PROJECT

The red bedrock mass examined in this paper has a bedding structure of easily slided strata.Its shear zones or weak intercalations are present among the relatively hard rock strata such as sand stone and soft rock strata such as silt-mud stone.The slope at the powerhouse site of Wawu Mountain Hydropower Project in particular is a day lighting slope whose bedding dip direction is almost the same as the slope dip direction.The sand stone strata and the silt mudstone strata are developed alternatively with low bedding dip angles of 10to 20.Shear zones or weak intercalations usually exist between the sand stone and silt mudstone under the action of tectonic movement,hyper-gene weathering and unloading.Landslides often take place along the shear zone or weak intercalation.It is under this geological background that the paleo-landslides such as Yanwan and Miaoziyan landslide at the powerhouse site came into being during the geological times.Eventually,the landslides are almost stable under the natural conditions.After their formation,the geomorphy of the landslides was changed because of the weathering and erosion.Or simply it was buried by slope debris.So it is not easy to find them using landslide geomorphic features alone.The Miaoziyan landslide is a buried paleo-landslide and was revived for the toe cutting and rainfall during the excavation.The stability of the Miaoziyan landslide under all work-condition was calculated.The calculation is based on the repeat shear test of the weak intercalation by the energy method upper bound limit analysis.Some treatments were used to prevent it from sliding further.Such re-landsliding would have side effect to the powerhouse construction.This paper can be used as a reference for the investigation and analysis of similar red bedrock mass paleo-landslides.