Study On The Mechanism Of Steep High Slope Evolution In Limestone Region Of The Three Gorges Reservoir Area

Limestone is widely distributed in the east of Sichuan of the Sichuan Basin,and the crust is uplifted and the river undercuts strongly in the later period.The topography differs significantly and steep high slopes are formed.A large number of dangerous rocks are developed on the steep cliffs in this area and are easily collapsed.This is a common geological disaster in the reservoir area and seriously affects people's lives and property safety.This paper has studied the evolution mechanism of steep high slopes in the limestone region of the Three Gorges reservoir area.It helps to promote the development of disciplines and geomorphology of disaster prevention and reduction,and it also has important guiding significance for the prevention and treatment of steep cliffs in the limestone region.This paper takes the evolution of Wangxia steep cliff in Wuxia Gorge of the Three Gorges reservoir area as an example,and uses geomorphology and fracture mechanics to analyze the geomorphological evolution process and evolution mechanics mechanism of steep high slopes in this area,and uses FLAC 3D software to analyze the secondary steepness of Wuxia Wangxia.The formation,evolution of the cliff and the formation and evolution of the dangerous rock on the cliff are simulated.The following results can be obtained:(1)The geomorphic features of the Wangxia cliff have a stepped layered landform feature.There are two significant levels of planes.The two levels of cliffs partially recede in the short term,and the longer time scales show that the two levels of cliffs are parallel and receding,neotectonic movement,In the process of merging and reorganizing the Yangtze River waters,the landforms of East Sichuan have been reconstructed obviously.The erosion of the huge Yangtze River water system has had a tremendous impact on the development of the landforms in the eastern Sichuan region.Erosion from the source caused the merging of the Yangtze River water system,and the erosion eroded the different rock layers of the cliff,and intensified the evolution of the steep slope under the action of external forces.(2)A large number of dangerous rocks are developed on the two-level cliffs composed of soft and hard lithologies.Due to the influence of multiple factors,the lateral unloading,the combination of soft and hard rocks,and the geological actions of external forces make the Wangxia steep cliffs dangerous.The rock mass has three typical structural planes,namely the horizontal primary structure surface,theunloading and splitting surface at the top of the slope,and the soft and hard rock interface at the bottom,so that the dangerous rock body has the characteristics of a masonry-like structure.Destruction There are three typical failure modes of tower-shaped fracturing seat collapse,plate dumping failure,and plastic flow-stripping failure.(3)Through the basic theory of fracture mechanics,the mechanical mechanism of the fracture and failure of dangerous rocks in the limestone region of the Three Gorges reservoir area was analyzed,and the method for determining the fracture mechanics of dangerous rocks was put forward.The case study of Wangxia dangerous rock in Wushan County was used as an example.It is considered that this method of judgment is more practical.(4)Using FLAC 3D software to simulate the evolution process of Wangxia second stage cliff and the deformation evolution process of Wangxia dangerous rock under three conditions of weathering,step excavation and groundwater.Lateral unloading stress redistribution occurs in the slope.During the river cutting process,stress differentiation occurs around the free surface of the river valley slope.The main stress trajectory is clearly deflected around the free surface.The closer to the empty surface,the greater the maximum principal stress.Parallel to this,the minimum principal stress is orthogonal to it.During the excavation process,the unloading rebound occurs around the free surface.The rebound amount shows that the closer to the slope the greater the value is 28 mm.The most important reason for the increased deformation of the Wangxia-Crisis Rock is the excavation.At the same time,the impact of the heavy rain has exacerbated the instability.The maximum displacement obtained is 0.72622 m,the maximum minimum stress is changed from the initial9.3585 MPa to 14.898 MPa,and the maximum maximum stress is changed from the initial 3.5095 MPa to 4.1306 MPa.(5)Through the simulation analysis of the formation and evolution process of the second-level steep cliffs and dangerous rock masses in Wangxia,the evolutionary process of steep slopes of Wangxia is roughly as follows: the crust is elevated,the river cuts down the strata,and the steep slopes of Wangxia are laterally high.Unloading,cliff formation,lateral unloading lead to stress redistribution of the slope,presenting stress concentration on the slope shoulders,forming a large number of steeply unloaded fracture structural planes,under the action of external forces such as weathering,groundwater and coal excavation Intensifying fissure expansion,the rockmass concentration in the soft foundation rock mass under the heavy pressure of the overlying hard rock occurred plastic flow extrusion in the direction of the free surface,and the slope rock mass collapsed,causing the upper hard rock to sit down and plastic flow occurred.-Cracking damage.