| According to the investigation of adit and slope field,the weathering unloading phenomenon on both sides of the study area is strong,the rock mass on both sides is severely broken,and the distribution of ductile shear zones is present on both sides of the study area.Abnormal unloading phenomena occur in some sections of adits.The fragmentary rock mass is distributed locally on the slope surface,and its integrity is poor.Long unloading fissures are often the controlling structural planes of rock slopes,and are sliding surfaces or boundaries that control the deformation and failure of slopes,which play an important role in the stability of slopes and the choice of dam sites.Based on the analysis of engineering geological conditions and structural characteristics of rock mass in the dam area,this paper analyzes the structural surface of the dam area,expounds the weathering and unloading characteristics of the study area,and comprehensively divides the unloading zone.On this basis,the unloading effect of the study area was studied by numerical simulation,physical simulation and unloading test.Combined with the unloading influence factor,the unloading mechanism of the study area was briefly analyzed.The main research contents and achievements of the thesis are as follows:(1)Through the statistical analysis of the structural planes on both sides of the dam area,there is no I or II level structural plane on both sides,and the dip angle of the fissure is medium to steep.The structural planes at all levels on both sides of the dam area are relatively developed in both the NE and NW directions,and the dip angles of the structural planes are mostly steep.According to the description of adit rock mass structure,the adit rock mass can be divided into block structure,mosaic structure,cracked structure,loose structure and rock mass structure type between these structures.(2)The degree of weathering of the rock mass in the project area is affected by the topography,faults and groundwater in the dam area,and the severity of weathering is quite different.Through analysis,the weathering of the rock mass in the engineering area is weak,and the weathering occurs mostly in the tectonic belt and the small fault development zone.The main weathering effect in the dam area is chemical weathering,while the physical weathering is weak.The mechanism of weathering unloading is discussed,and the weathering unloading phenomenon in the study area is briefly described.The unloading zone is comprehensively divided by three quantitative indicators: the crack opening degree,the flat seismic wave velocity and the wave velocity ratio.(3)Analysis of the variation characteristics of dacite under unloading conditions,it can be seen that the specimens are mainly axially deformed during the loading phase.When the confining pressure is unloaded,the specimens will undergo lateral expansion and volume generation.When the confining pressure is unloaded to a certain extent,the samples will be destroyed.With the confining pressure increases,the peak strength of the sample will increase when the confining pressure is increased.Under the same confining pressure condition,the faster the unloading rate,the more easily the samples are destroyed.Under the same confining pressure condition,the faster the unloading speed,the smaller the confining pressure difference when the samples are broken,and the smaller the elastic modulus of the samples.(4)Using the flac software to numerically simulate the evolution process of the valley,it is found that the maximum and minimum principal stress of the slope gradually decrease with the continuous cutting of the valley.The displacement of the slope in the x direction is toward the valley,and the displacement gradually increases with the evolution of the valley.In the valley position,the displacement is always the smaller value distribution,and the larger displacement is mainly distributed in the ductile shear zone.The distribution range and depth of the plastic zone of the slope increase continuously with the valley cut.The plastic zone distribution is mainly concentrated in the right bank ductile shear zone and the right bank slope position,and the plastic zone is less distributed in the left bank ductile shear zone.According to the numerical simulation results,the ductile shear zone has a great influence on the unloading of the slope rock mass.(5)Through the physical simulation test of the dam area,it is found that the stress of the slopes on both sides of the slope gradually decreases with the undercut of the valley.At the same elevation,the stress change of the rock mass inside the slope is smaller than that of the slope.When the upper rock mass is cut under the late river valley,the stress does not change substantially.The left bank slope cracks during the river valley cutting process,and the crack gradually extends and widens along with the river valley undercut.During the unloading process,cracks and small scale collapse appeared in the local position of the slope surface.The slopes with the valley undercut produce a certain displacement to the valley direction,and the higher the elevation,the more obvious the displacement phenomenon.(6)In the long-term geological history,the river bank slope forms the current form.With the change of the terraces and free surfaces,the stress inside the slope was gradually released and redistributed.And the slope body is unloaded,and the slope rock mass structure and structure are changed.The current topography has been formed through long-term epigenetic transformation and physical and chemical weathering.Through the analysis of physical simulation,numerical simulation and unloading test,combined with the actual conditions of the dam area,the unloading mechanism of the study area is briefly analyzed. |
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