| According to the field investigation,unloading of the dam site on both sides is intense and complex,and there is the characteristics of asymmetrical on both sides.The unloading depth of right bank is obviously stronger than the left bank,and there is the phenomenon of some local unloading depth is sharply higher.This causes the rock mass is badly broken and the integrity is poor.The unloading fracture by unloading effect may be the control structure surface in the bank.There is cataclastic rock mass during the development of unloading of shallow slope.These can lead to a series of engineering geology problems.According to the basis of the research on the engineering geological conditions and structural characteristics of the rock mass on both sides of the dam site,this paper describes the characteristics of the unloading development of the banks on both sides of the strait,and analyzes the characteristics of unloading depth and unloading distribution,deformation and failure.And summarizes the abnormal development of unloading and the abnormal phenomenon of local unloading.Analysis the difference in Slope unloading of dam site bank from the factors of unloading development.Combined with the history of river valley evolution,the mechanism of unloading and formation and evolution process of river valley slope are revealed by means of geological mechanism process analysis,physical simulation and numerical simulation.The main contents and results of this paper are as follows:(1)Through the study of the development characteristics of the structural plane of the rock mass on the two sides of the dam,it is concluded that the primary structure mainly includes the flow layer,the steep columnar joint.The physical and chemical belts and alteration zones formed by the contact surface of intrusive rocks and basal rocks and tectonic dynamic metamorphism and magmatic-tectonic hydrothermal activity.Tectonic structural planes are mainly tectonic extrusion under the action of medium and small fault,interlayer compressive belt(surface)and tectonic fissures,born superficial structural plane is a new slope surface.slope,and the surface modification of unloading fissure and along the existing columnar joints or steep dip Angle fracture tension produced by the tension fracture.(2)Through the study of unloading of rock mass on the bank slope of the dam site,the unloading macroscopic characteristics are obtained.The unloading of the bank slope is based on the boundary of elevation 3000 m,the unloading relaxation phenomenon of the upper rock mass is obvious,collapse,the dangerous rock body and the deformable body are common,while the shallow surface part of the rock mass is open to the shallow surface.Cracking is the main way,and the unloading degree of rock mass gradually decreases from the superficial part to the deep part of the slope.(3)Through the study of the index zoning of the unloading zone,the qualitative index classification standard given by the standard is adopted,the unloading zone is divided by the quantitative index index of the open fissure intensity and cumulative opening of the rock mass and the seismic wave velocity of the adit.The quantitative index can reflect the degree of unloading well,and the density of the open fissure in the 5m section is determined.The strong and weak unloading boundaries are greater than 10 and 2-10 respectively,and finally the results of comprehensive division are obtained(4)The stress field of the river valley slope evolution is analyzed by FLAC.The results show that the direction of the maximum principal stress in the slope is gradually shifted to the bank slope along with the valley cut down,and the direction of the minimum principal stress is perpendicular to the bank slope,the local tensile stress appears on the slope top and the slope table,the stress concentration in the bottom of the valley and the right bank erosion are in a certain range.The stress magnitude of the shear zone and the shear zone decreases,and the local stress differentiation occurs.(5)Using the UDEC discrete element to simulate the formation and evolution process of the river valley slope and analyze the deformation and fracture,the result shows that along with the river valley cutting,the slope of the river banks will be deformed,the displacement is moving towards the river valley,the plastic zone is deepened,the unloading displacement of the right bank and the plastic failure area are larger than the left bank,and the alteration shear is shear.The yield failure is more obvious and the bending collapse deformation is gradually destroyed.(6)The physical simulation test on the formation and evolution of the slope unloading on the bank shows that the rock mass in the shallow surface of the bank slope in the valley of the river valley produces a clear fracture of the unloading fracture,and the fracture of the right bank is more obvious;the monitoring data shows that the pressure unloading in the slope is reduced,the horizontal displacement to the face to the air surface becomes larger and the slope surface is shallow.The pressure and displacement of the part are larger than that in the deep,and the pressure and horizontal displacement of the measuring point on the upper part of the slope are larger than the lower part,and the right bank has a larger change than the left bank,and the unloading of the upper and right banks is more serious.(7)By the river bank slope of numerical and physical simulation study show that the formation of river bank slope unloading of one-time complete evolution is not a short time,but with the incised valley,the airport surface changes constantly adjust,the gradual release of slope stress,adjust the distribution of temporary stability,in the bank slope lithology,rock mass structure,structural plane structure early condition,the basic features of bank slope under dynamic condition and status of tectonic stress,such as weathering,born after a long period of superficial modification effect,gradually formed the current bank slope unloading characteristics.Dacite in high strain can be stored and the lithologic characteristics of brittle deformation result in overall is strong on both sides of the bank slope unloading degree and the time effect of supergene transformation led to the upper slope unloading effect is relatively lower,dacite overflow surface in the area(like)the overall flat structure characteristics of the left bank and right bank alteration belt and ductile shear zone of asymmetric exposed caused on unloading obviously in the left bank of the serious results. |
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