Structural Feature Analysis And Research On Deformation And Failure Mechanism Of Dangerous Rock In The Red Bed Zone Of Renchi Expressway

Dangerous rock collapse is one of the most common geological disasters in Guizhou mountainous areas.Most highways in Guizhou Province pass through mountainous areas,and there are a large number of dangerous rocks and falling rocks on both sides of the expressway.This paper takes the dangerous rocks in the red section of the Ren-Chi Expressway as the research object,and uses two methods of manual field investigation combined with drone surveys to conduct detailed investigations on 12 dangerous rock slopes and 21 dangerous rocks along the line.According to the on-site investigation results and the interpretation results of the unmanned aerial vehicle three-dimensional model,the distribution law of dangerous rocks and the structural characteristics of dangerous rocks in the study area are analyzed and studied.The control factors and deformation failure modes of the dangerous rock in the study area are analyzed,and two typical dangerous rocks with different failure modes are selected for the PFC numerical simulation study,which provides technical support for the research and prevention of dangerous rocks along the red-bed section of the Ren-Chi Expressway.The main research contents and achievements are as follows:(1)Through data collection and sorting,the engineering geological conditions of the study area were ascertained,using drone low-altitude photography technology to take aerial photographs of 12 dangerous rock slopes,and establish 12 drones three-dimensional surface models,based on the three-dimensional model,information such as the size of the dangerous rock,the development of the cavities,and the occurrence of structural planes are interpreted.(2)Analyze the development and distribution of dangerous rocks based on the survey results and interpretation results.The results show that the dangerous rocks are all developed in the Jiading Group Member 1(Kjd~1)formation;the distribution elevation is between 310m and495m.Mainly located at ridge cliffs,steep slopes,gully cliffs and steep slopes,where the slopes of the slopes are all greater than 60°.(3)Analyze the structural characteristics of the dangerous rock in the study area from the aspects of the dominant grouping of the structural planes of the dangerous rock,the development density of the structural planes,the development characteristics of the unloading cracks,the development characteristics of the cavities,and the structural types of the dangerous rocks.The results show that there are three sets of dominant structural planes in the dangerous rocks along the line,which are a set of nearly horizontal bedding planes and two sets of nearly vertical structural planes.The development density of structural planes is obviously affected by lithology and layer thickness,and the development density of sandstone joints is lower than that of mudstone.Among them,a group of structural planes nearly parallel to the slope direction are unloading structural planes,which are formed by the undercutting and unloading of Chishui River;There are cavities of different depths and shapes under the dangerous rocks along the line,and the depth of their development is between 0.51m-4.01m;There are two main types of dangerous rock structures along the line:block-like structure and sand-shale interbedded structure with unequal thickness.(4)Through the analysis of the controlling factors of the deformation and failure of dangerous rock,dangerous rocks in the study area are mainly controlled by factors such as stratum lithology,topography,differential weathering,unloading structural surfaces,cavities,and human engineering activities.Among them,unloading structural surfaces and concave rock cavities play a major role in controlling the deformation and failure of dangerous rocks.The FLAC3D software was used to carry out a numerical simulation study on the stress field distribution in the valley cutting process,and the results showed that the in-situ stress of the valley occurred stress deflection on the valley slope during the river cutting process.The original ground stress is gradually restored to the interior of the slope,a zone of stress concentration and increased shear strain appears at the bottom of the valley.In the process of valley undercutting,the magnitude of the principal stress field continuously decreases,indicating that the strain potential energy in the rock body is constantly decreasing during the process of valley undercutting,which provides conditions for the formation of unloading structural planes.(5)Through investigation and analysis,the dangerous rocks in the study area mainly have two failure modes:dumping and falling.Through PFC2D,the two typical dangerous rocks with two failure modes are numerically simulated and analyzed,and the deformation and failure of the two dangerous rocks with different failure modes are qualitatively analyzed in terms of contact force and displacement.