Study On The Deformation Failure Mechanism Of Metamorphic Rock Slope Of Shiyan To Tianshui Expressway

Total mileage of Hubei-Shaanxi boundary to Ankang section of Shiyan to Tianshui expressway which is from Baihe County to Hanbin District, across Baihe and Xunyang, is about 127 kilometers. The expressway passes through metamorphic rock area in Qinling Mountains. Due to the regional geological environment, the metamorphic rock slopes have special geological features and law of deformation and failure. Based on field survey, this article is about laws and factors of deformation and failure of metamorphic rock slopes at Shiyan to Tianshui Expressway, and to simulate excavation to slopes at different conditions with finite element method. Results are as follows:1.According to slope structure types, the metamorphic rock slopes are divided into blocky structure slopes, layer structure slopes, cataclastic structure slopes, granular structure slopes and base structure slopes. Types of deformation and failure of slopes can be divided into wedge failure, bedding sliding, cut layer sliding, toppling failure, and circular sliding.2.The slopes are good stability, which include block structure slopes, crossing-oblique crossing layer structure slopes, countertendency layer structure slopes with hard rock. Meawhile, the stability of fractured structure slopes, granular structure slopes and base structure slopes is poor, accompany with circular sliding. Slopes of consequent layered structure are prone to slide, and countertendency layer structure slopes with soft rock are less stable to cut layer sliding and toppling failure.3.Many factors contribute to the deformation and failure of slopes, including micro-geomorphology, lithology, slope structures, rock mass discontinuity and structural characteristics, rainfall and groundwater, construction and excavation and so on. Micro-geomorphology of slopes affect weathering degree of rock to the stability. The horizontal displacement of slopes is influenced by excavation, which form excavation relaxation region in excavation process. The shear stress concentration occurs at contact surfaces of different rock. After excavation, the largest shear strain occurs at top and toe of slopes. The stability of slopes is effected by water, which at the rainy season slopes are damaged. When anchor bars are in excavation relaxation region, anchor frame beam support as slope protection has little effect on slope stability. Using the reasonable prestressed anchor cable frame beam, the displacement of rock mass decrease, and range of excavation relaxation and shear deformation of slopes narrow, which can significantly increase the slope stability.