瓦屋山水电站厂房区红层岩体古滑坡稳定性研究

红层岩体以其岩体结构的软硬相间及软弱夹层发育而在边坡稳定方面表现为"易滑地层"。瓦屋山水电站厂房区边坡为顺向坡,砂岩类岩石与黏土岩类岩石呈缓倾、互层状(倾角10°~20°)产出。构造与表生改造作用下,在这两类软硬相间的岩石界面上常形成分布较为连续的软弱夹层,这类岩体较易沿软弱夹层产生顺层滑动。地质历史时期,瓦屋山厂房区就是在这样的地质背景下,形成了多个古滑坡体,如颜湾和庙子岩古滑坡,它们在自然状态下已基本稳定。随后因风化剥蚀等作用,古滑坡体形态被改变或被来自后缘斜坡的坡残积层所掩埋,使其在勘察期间难以被发现。庙子岩滑坡即是这样一个被掩埋的古滑坡体坡,施工开挖过程中,由于切脚及降雨作用,使其重新滑动复活。本文以反复剪试验得到的滑动面抗剪参数,采用边坡稳定极限分析能量法(Energy Method Upper Baond Limit Analysis),简称EMU法,对庙子岩古滑坡在各种工况下的稳定作了计算,并据其结果采取了相应的抗滑处理。本文可作为红层岩体地区该类型滑坡勘察和工程处理设计的参考。

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 10°to 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.