Study On Failure Mode And Stability Of Jurassic Sand-mudstone Bedding Slope In The Three Gorges Reservoir Area

In China,the failure types of bedding rock slopes combined with soft and hard rocks are complex and difficult to control.Jurassic sand-mudstone bedding slopes in the Three Gorges Reservoir area are a very representative type.Problems that are prone to occur and frequently occur are studied from the aspects of soft rock properties,genesis of weak surfaces,slope angle,rock formation inclination and its combination form,joint distribution,and the main inducing factors of landslides are analyzed.Conduct failure mode and stability studies.The research results can provide a theoretical basis for the instability mechanism and stability evaluation of sand-mudstone bedding slopes caused by road excavation and cutting slopes,and provide support for the prediction and prediction of bedding rock slope instability.The main research work of this paper includes the following:(1)Conduct investigation and research based on typical landslides in the study area.Taking the typical sand-mudstone bedding rock slope as the research object,investigate and clarify the natural geographical conditions,geological structure,rock formation,landslide material composition,landslide shape and scale in the landslide area,and preliminarily analyze this type of landslide.The cause of the formation,laying the foundational background of engineering geology for the follow-up research.(2)Research on landslide-inducing factors based on the properties of soft rock and the origin of weak surfaces.Firstly,the internal and external factors affecting the stability of this type of slope are summarized,and it is proposed that "the water seeping from the cracks in the sandstone layer flows to the upper part of the mudstone layer,and the mudstone softens when it encounters water,forming a weak layer" is one of the main reasons for the instability of the slope.Through mudstone disintegration test and sand-mudstone model softening test under the condition of fissure water,the origin of weak rock formation was studied,and the microstructure,sample characterization and mineral composition of sand and mudstone were analyzed by field emission electron microscope scanning and X-ray sample diffraction test,further explained the development process of the induced causes of the Jurassic sand-mudstone bedding landslide.(3)Research on failure mode based on physical model test.Through the failure test of soft and hard interbedded rock slope,the relationship between the leading edge slope angle and the dip angle of the soft interlayer was explored when the bedded rock slope was damaged.The research results show that the stability of bedding rock slope is controlled by the density of layers and joint planes.When the slope contains multiple weak planes,the front edge of the slope is easy to be damaged along the planes and the joint penetration plane of the trailing edge after excavation..(4)The failure mode and instability mechanism of the Jurassic sand-mudstone bedding slope are analyzed,and the stability of the case slope is calculated based on the limit equilibrium method.The PLAXIS 2D finite element software is used to simulate the changes of the slope during excavation and rainfall.The PLAXIS 2D finite element software is used to simulate the changes of the slope during excavation and rainfall,and the analysis shows that the sliding front section is linear and close to the weak surface.The tensile cut-off points are mainly distributed at the toe of the excavation at the trailing edge and leading edge of the slope.