大光包滑坡岩体碎裂特征及其工程地质意义

THE ROCK MASS CATACLASTIC CHARACTERISTICS OF DAGUANGBAO LANDSLIDE AND ITS ENGINEERING GEOLOGICAL SIGNIFICANCE

"5·12"汶川地震发生六年以来,对地震诱发最大的大光包滑坡开展了工程地质测绘、声波检测、钻孔取芯、电镜扫描等一系列工作,研究表明该滑坡滑带产生于震旦系灯影组三段(Zd3)白云岩的层内错动带。综合研究揭示滑床岩体碎裂化宏观特征如下:滑面以下0~1 m岩体呈砂土状,砂粒含量占到60%以上;1 m以下岩体平均声波波速2 500~3 000 m/s,完整性指数趋于0.15~0.77,岩体损伤程度总体上随滑床深度增加而减小,而滑面下同一深度岩体损伤程度随滑床高程的增加而增大,局部有差异性破碎。另一方面,微观研究揭示滑带岩体压剪晶体沿解理面折扭断裂,穿晶裂纹发育,表现为部分晶体松动架立,晶间连接丧失。研究揭示的工程地质意义:(1)滑带岩体性质主要受控于层内挤压错动的泥质花斑状白云岩,该层成分复杂,风化程度高,节理发育,完整性差;(2)"5·12"地震使滑带岩体产生强烈的剪切破坏(拉张和压剪破坏)和翼裂纹扩展,岩体的抗剪强度指标及完整性系数剧降,岩体质量劣化,在启动后巨厚滑体的碾压与揉搓作用下,滑带岩体的摩阻力进一步降低。综上,大光包滑坡滑带岩体损伤碎裂化是地震荷载作用下岩体内部缺陷动态演化的累进过程,滑带所在的地层岩性及岩体结构特征为其主要内因,强震荷载是其关键的外在诱因。

Over the past six years after'5·12'Wenchuan earthquake,we have carried out engineering geological surveying,acoustic detection,coring-drilling,electron microscope scanning and other works to the Daguangbao landslide,which is the largest landslide induced by Wenchuan earthquake. Studies showed that the sliding zone of this landslide occurred in dolomite intraformational disturbed zone which was located in the third section of Denying group of Sinian system(Zd3). Comprehensive studies reveal the macroscopic characteristics of the fragmentation rock of slide bed as follows:the rock presents sandy soil within the 0–1 m depth below sliding surface,which the sand content occupy more than 60%;1m below the sliding surface,the average rock acoustic velocity is range in 2 500–3 000 m/s,in addition the integrity index of the rock tends to 0.15–0.77. On the whole,the damage degree of the rock mass generally decrease with the depth increase of slip bed,but under the same depth those increase with the elevation increasing,except the local difference broken. On the other hand,microscopic study reveals that the compression-shear crystal of rock mass of slip zone is fold and torsional fracture with lots of transgranular crack,which shows parts crystal loose and intergranular connection loss. Study reveals the significance of engineering geology as follows:(1) Property of the rock mass in sliding zone mainly controlled by argillaceous graniphyric dolomite of intraformational extrusion dislocation,which the composition of this layer is complicate with the high degree of weathering,joint development and poor integrity;(2) Under '5·12'Wenchuan earthquake,the rock mass of slide zone generated strong shear failure(tensile and compressive shear failure) and wing crack extend,which caused sharp drop of the rock shear strength index and the integrity coefficient,thus deterioration of the rock mass. Furthermore,the rolling and rubbing action of thick sliding body afther starting further promote frictional resistance reducing in the sliding zone rock mass. In summary,the fragmentation of rock mass damage of Daguangbao sliding zone is a dynamicly progressive evolution process of rock internal defects under seismic load,the lithology and rock structural characteristics of slide zone are the main intrinsic factors,earthquake loads are its key external incentives.