Study On The Mechanical Mechanism And Evolution Characteristics Of Toppling Deformation In Thin Anti-dip Slate Slope

Toppling of rock mass is the deformation model,which is common in steep pitch anti-dip layered slope,that layered rock mass bends to free face under the effect of comprehensive agent,such as geostress,gravity or groundwater,and extends to the deep gradually.The ductility bending toppling deformation developed in thin layer soft slope has a huge scope of influence and can induce giant landslide,which is a great threat to the project.So study of the mechanics mechanism and characteristics of toppling deformation in thin anti-dip layer slope and stability evaluation based on kinematic characteristics is of great significance to scientific practice and engineering applications.Taking the thin anti-dip slate slope in right dam abutment of Zhala hydropower station dam site on Yuqu River in Xizang for an example,the time-sensitive characteristics of toppling deformation are explained by rheological theory in this paper and rheological experiment of cantilever beam and frame-type model test are completed to figure out mechanical mechanism,evolution process and characteristics of toppling deformation.The main conclusions are as follows:(1)Strata can be viewed as a cantilever beam with one fixed end and one free end during the process of toppling deformation.It can be concluded through rheological experiment in which rock beam deforms under the effect of uniform load created by weight that rheological process can be divided into 4 stages: instantaneous deformation stage,lateral creep stage,steady deformation and accelerated creep stage.Fracture develop from top to bottom in the accelerated creep stage which is considered to be unsafe.Strain acceleration(a)can be a discriminant index to distinguish the different status during the whole process of deformation.It can be considered that,linking to the related achievements in landslide early warning,the rock beam is in the lateral creep stage with strain acceleration is less than-1.02×10-4/h-2,in the steady deformation with strain acceleration between-1.02× 10-4/h-2 and 1.45× 10-4/h-2 and in the accelerated creep stage with strain accelerated more than 1.45×10-4/h-2.Considering the anti-dip slope as the superposition of rock beams,this conclusion can be a reference for slope stability evaluation.(2)The bending rheological process can be divided into instantaneous elastic deformation,instantaneous plastic deformation,viscoelastic deformation and viscoplastic deformation by deformation properties.One seven-element rheological model is achieved which consists of hookean model,kelvin model,bingham fluid and a improved non-linear viscoplastic element to describe the characteristics of bending rheological.It is proved that the model can describe the rheological characteristics under different stress conditions by characteristic analysis and curve fitting of the rheological model.The depth of failure and development are estimated in this paper by taking the mutation of strain rate and the point with zero strain as criterion,which is based on the rheological constitutive equation of bended rock layers.The lithological combination conditions are proposed mathematically according to the characteristics of constant development depth and that the depth of development is greater than fracture.(3)Based on the rheology constitutive equation of bending rock beam,the developing depth and bend depth can be calculated by using the zero strain and strain acceleration which is greater than it is in the steady state deformation stage.Lithologic combination condition mathematically is achieved by taking use of the relationship that developing depth is more than bend depth.(4)The frame model test provides the data support for the study of the evolution stages of the toppling deformation by using the kinematic indexes.It can be found after the frame model test of the geological process that the toppling of the whole slope can be divided into initial creep stage,constant creep stage and then evolve into a large landslide because of transfixion of potential deflection surface.When it comes to the rock in shallow surface,the more easily occurring deformation and failure is the failure of rock beam bending and fall,which is the most common types of damage in toppling failure.Dividing the evolution stage of the process of toppling deformation by kinematics indexes can be beneficial to predict the trend of toppling deformation so as to evaluate the stability of toppling deformation more pertinently.(5)It can be found through frame model test that the strain acceleration waves near zero basically instead of constanting to zero when it is in constant creep stage.Once the slope failure occurs,the acceleration will increase rapidly and break through the upper limit in constant creep stage.After comparative analysis of deformation index,such as displacement,deformation rate and acceleration,it is concluded that acceleration can be the index for stability analysis of toppling slope and a>a2 can be warning criterion of toppling failure.a1 and a2 can be obtained by plenty of monitor data and simulation tests.