| The study area is located in the near intake on the right bank of Maji hydropower station in Nu River of Yunnan, in which the phenomenon of deformation and fracture controlled by low-angle and tilt-valley structural planes is very obvious, whose macro-combination mode shows sliding-fracturing. However, these structural planes did not cut and expose to the slope toe, but buried inside the toe or below a certain depth of the valley. And according to the views of traditional engineering geology and rock mechanics is difficult to understand the cause of this phenomenon.Therefore, based on the understanding of engineering geological conditions for the study area, the author conducted the site macro investigation and interior microscopic test analysis for the existing signs of deformation and failure in the slope, so as to determine the combination mode and analyze qualitatively the mechanism of slope deformation and failure. Meanwhile, with the numerical analysis software FLAC3D to simulate the evolution of the slope, analyzed the changes of the stress and displacement fields in the slope, and further demonstrated genetic mechanism of slope deformation and failure. Finally, using two-dimensional limit equilibrium method and finite element strength reduction method, calculated and analyzed the stability of natural slope and excavation slope, thus supported reasonable proposals for excavating and supporting of the intake. The main conclusions are as follows:(1) The existing phenomena of deformation and failure have mainly manifested in two aspects, one is the shearing-slipping phenomenon along the low-angle and tilt-valley structural planes in the lower part of the slope, the other is the tensile fracture phenomenon along the mild-steep fissures in the upper part of the slope. It shows the sliding-fracturing deformation and failure mode, however, compared with the common sliding-fracturing mode, these low-angle and tilt-valley structural planes did not cut and expose to the slope toe, but extends to the below of the discontinuity between bedrock and Quaternary.(2) According to the field survey and indoor microscopic test, and combined with the geology-rock mechanics environmental conditions of the slope development, the phenomenon of slope deformation and fracture is a sliding-fracturing mode dominated by the softening effect of rock in the valley bottom. That is, the granulite in the valley bottom (slope toe and valley below) was compressed because of weathering and softening, meanwhile, alaskite vein were crushed inserting the granulite. Resulting in the low-angle and tilt-valley structural planes (ft 3 fault as the representative) buried in deep slope sheared and dislocated, and further causing the mild-steep fissures in the upper part of the slope migrated and intensified to the deep.(3) On the basis of qualitative analysis, putting the B6-B6’geological profile as a geometric model, using FLAC3D software to simulate the evolution process of slope, analyzing the stress distribution rule, deformation characteristics and the changing rule of the plastic zone of the slope in each period. The results showed that, the stress distribution had little change and the displacement difference was not obvious in the two walls of structural planes in the early stage of valley cutting and rock weathering; the maximum principal stress increased and the minimum principal stress reduced near the surface structures after the second times cutting of river valley; as the weathering of rock in the slope toe and the bottom, the displacement difference of two walls increased significantly in the current valley period, which shows rock mass in the slope had obviously deformed. The calculation results verify the qualitative analysis well.(4) In this paper, the example of slope deformation and fracture revealed the existence of the softening effect of valley bottom. For the different lithologies, different slope structures and different stages of valley cutting, the above effect’s influencing extent and performing forms may be different, but it is with the effect caused by changing slope shape (due to natural cutting) to the slope exist in the entire processes of valley formation and evolution, which is a kind of geological function having universal significance.(5) Using the limit equilibrium method (Slide) and the finite element strength reduction method (Phase2.0), respectively analyzing the stability of natural slope and excavation slope in various operating conditions. The calculation results show that natural slope and excavation slope is basically stable or stable in the general conditions, Fs>1.05; while the excavation slope is less stable in the extreme earthquake and storm condition. Therefore, according to the arrangement of the intake, should reduce the amount of excavation, move the excavation line out, or support during the excavation... |
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