| Landslide,which is one of the most common natural disasters,is not only widely distributed,but also have caused serious damage.In China,mountains and hills are widely distributed,as well as landslides.Due to the complex geological conditions,landslide has a severe impact on China.Stabilizing pile is an effective tool in controlling landslide.Since its' easy construction,the stabilizing pile is widely used in the landslide control project.In the rock creep phenomenon,the rock internal structure continues changing with time under a constant load.This geotechnical behavior is widely observed.The rock creep negatively affects the rock strength,and this decrease in the rock strength further affects the control effect of the piles and the long-term stability of landslide.The Three Gorges Projects is the largest hydro-project of world.A significant number of large-scale landslides and collapse have been found in reservoir area,the bedrock of which is mostly the Jurassic stratum.Jurassic sand-mud bedded rock is major lithology in this area.During the evolution of landslide,the creep behavior of bedrock will cause damage strain.The strength of rock decrease as time goes on.For the controlled landslide in the Three Gorges,the creep behavior of bedrock in anchoring section will lead the decrease of rock strength.This will affect the anchoring affects of the piles,which lead to the stability of the controlled landslide.Thus,it is necessary to consider the creep behavior of the rock mass in anchoring section and its effect to the control effect of the piles.It is also important for evaluating the long-term stability of the controlled landslide.Taking the Jurassic sandstone and mudstone as object of study,this paper performed the triaxial creep test on the sandstone and mudstone under different confining pressures,studied the creep behavior of two kind of rock mass,established the creep model,and analyzed the long-term strength.Based on the established model,the constitutive equation of interbedding rock mass was deduced.An ideal model of landslied-stabilizing pile system has been established,considering the creep behavior of interbedding rock mass in an anchoring section.Analyzed the control effect of the piles,considering the creep behavior of rock mass in an anchoring section.Based on the above researches,the main results of this paper are as follows:(1)Short term mechanical property of Jurassic sandstone and mudstoneThe basic properties of Jurassic sandstone and mudstone were studied by taking the physical mechanics tests.The strain-stress curve of rock can be given by uniaxial and triaixial compression test.Through the curve,both the deformable features of uniaxial and triaixial compression can be divided into four stages: initial compression stage,linear elastic deformation stage,plastic yielding stage and plastic softening stage.The failure mode of rock samples under two conditions are different: the sample failed by brittle fracture in uniaxial compression test and failed by typical shear failure in triaixial compression test.According to curve of elasticity modulus and stress,the yield stress under different confining pressure can be driven of.The short-term strength can be calculated by Mohr-Coulomb Failure Criterion.The elastic modulus of sandstone is three times bigger than mudstone.For the interbedding rock,the unmatched elastic modulus will lead the uncoordinated strain.(2)Creep behavior of Jurassic sandstone and mudstoneIn the process of the triaxial creep test,the multi-step loading technique was applied.The test results show two stages(initial creep,steady-state creep)when the deviatoric stress is lower than the yield stress,show three typical stages(initial creep,steady-state creep and accelerated creep)when the deviatoric stress is greater than the yield stress.The accelerated creep strain is the key component of total strain.The strain-stress curve considering rock creep behavior consist of four stage: initial compression stage,linear elastic deformation stage,plastic yielding stage and plastic softening stage.The rock creep strain and steady state strain rate decrease with time increase under same deviatoric stress.This means confining pressure has negative effect on the rock creep strain.Under the same confining pressure,the steady-state stage strain sate increase with deviatoric stress.The instantaneous elastic strain increases with the deviatoric stress.The strain rate of steady state stage of sandstone is lower than mudstone.This means under triaxial stress state,the creep deformation of mudstone is larger than sandstone.(3)Established the nonlinear consititutive model of Jurassic sandstone and mudstoneA nonlinear viscoelastic-plastic creep model is established to describe the creep behavior of sandstone and mudstone.Based on the hyperbolic theory,Burgers model is improved,the improved Burgers model can well fitted the linear relationship between initial elasticity modulus and deviatoric stress,it is also well fitted the viscoelasticity behavior of rock.A nonlinear viscoelastic-plastic creep model is developed to describe the accelerate creep stage.Through comparison between the model and test curve,the viscoelastic-plastic creep model can well fitted the entire process of rock creep.Applied the generalized mises criterion and elastic-plastic theory,three-dimensional creep model is established.The long-term strength is taken as the critical stress that causes the steady-state creep.With the developed creep model,the long-term strength of the sandstone and mudstone can be derived as well as the linear relationship between steady creep strain rate and deviatoric stress.Both long-term compression and shearing strength are lower than short strength.(4)Established the nonlinear creep model of inter-bedding rock and compiled the numerical program of the modelThe stress-strain relationship is homogeneous in macro level,depends on rock mass characteristic of two rock at micro level.Considering the displacement compatibility of cell,the relationship between strain-stress tensor and the volume content and strain tensor can be derived.Calculated by the Cosserat medium theory,equivalent elasticity modulus and poisson ratio can be derived.Based on the rock creep model and elastic-plastic theory,incremental form of element creep model can be derived.Because of rock creep,the share of strain of sandstone and mudstone changed with time in the numerical model.This will cause the strain redistribution problem.A numerical program is compiled to simulate the stress redistribution caused by rock creep.To verify the program of established model,a numerical is developed,the result show the model of inter-bedding rock can fit the creep behavior of rock well.(5)Control effect of the piles considering the creep behavior of inter-bedding rockmassIn the numerical simulation of bedrock creep behavior in different operating condition(different width and depth of pile),the deformation around pile and the distribution law of bending moment and shear is influenced by the creep behavior of inter-bedding rock mass.The result shows the time-varying rules of displacement around pile is the same as rock strain.Strain consist of instantaneous strain and creep strain.The main displacement is translation.The creep strain is major part of total strain,the strain of initial creep is major part of creep strain.The displacement mode changed during the evolution of model.The pile deformation of pile is RB.?Influenced by the rock creep behavior the pile translated while turning around the bottom.The deformation of the pile turns to RBT pattern.The value of bending moment and shear obviously decreased,considering the creep behavior of bedrock.The maximum bending moment and shear decrease with the increase of time,the distance to the top of pile increase with the increase of time.Considering the creep behavior of bed rock,the anchoring force turns lower by time,which means the anchoring effect decreased with the increase of time.The effect on the deformation of the rock around slide depend on the depth and width of the piles. |
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