Study On Deformation Induced By Excavation Of High Bedding Rock Slope

This paper is based on the national science and technology support program project that is “the control theory and dynamic control technology research of the highway subgrade in Southwest China(NO: 2015BAK09B00)”.The route of “rock – layer – rock slope” is taken to research the deformation induced in the progress of excavating the soft and hard rock in the southwest mountainous area.The combination method of laboratory test and numerical simulation is used to analyze the variation law of mechanical indexes of sandstone mudstone under different unloading rates.The contact surface and thin layer element theory are used to simulate the interfacial properties of layered rock mass.The distribution of stress and deformation of the bedding rock slope and its influence on numerical simulation are discussed.Specific research work and achievements are as follows:(1)Through the rock test,the failure modes of sandstone mudstone under different stress states are obtained.In the tensile strength tests,sandstone rupture is circular arc and vertical micro cracks and vertical slit width;mudstone fracture and vertical fracture is bow shaped.In the three axial compression tests,the elastic modulus of sandstone increases with the increase of confining pressure,and the tensile strength and tensile strength of mudstone are increased.In the three axis unloading test,oblique line transition of sandstone burst into a "Y" type,which is compression shear tensile failure;and mudstone is compression shear failure.With the axial strain curve,the confining pressure is mostly two straight lines and the deviatoric stress is in the three segment.(2)The mechanical indexes of sandstone and mudstone have distrinct damage and degradation to under the condition of different unloading.When the confining pressure is low,the sandstone increases slowly and then tends to be stable with the increase of unloading rate.When the confining pressure is high,the mudstone decreases first and then increases with the increase of unloading rate.The maximum unloading ratio of sandstone and mudstone is at about 0.5,and firstly decreases and then increases slowly with the increase of unloading rate.With the unloading rate increases,unloading modulus of sandstone decreased firstly and then tends to be stable,the deformation modulus decreases to a steady state as the unloading rate increased;unloading modulus of mudstone increased firstly and then decreased,the deformation modulus is decreased slightly with the increasing trend of unloading rate.(3)Both contact surface and the thin layer element are used to simulate the shear characteristics of layer interface between sandstone and mudstone.In the nonlinear stage,the stress-strain curve of the contact surface method is hyperbolic,and the curve of the thin layer element method is linear after the ultimate shear strength.Both of them can simulate the shear characteristics,but the former is difficult to simulate the large excavation area,and the data of the latter is discrete.Therefore,the thin layer element method can better reflect the distribution of shear stress.(4)Stress concentration on the toe of slope is induced by excavation,which causes the phenomenon that there exists deformation in the platform along level direction and slope surface toward free face.The horizontal deformation of the excavation surface decreases with the increase of the shear modulus,and the deformation at the midpoint of the platform increases with the increase of Poisson's ratio.The vertical deformation of the excavation platform increases with the increase of the thickness of the first layer and then decreases,and the serrated phenomenon of the inter layer stress becomes more and more obvious with the increase of the dip angle of the strata.The horizontal deformation of excavation surface increases first and then decreases with the increase of excavation width,and its maximum value is located near the slope shoulder.The phenomenon of stress concentration is gradually eliminated with the increase of excavation stage on the excavation surface and slope toe with excavation stress concentration series increases gradually eliminate.