Geological-mechanical Response During Large-scale Excavation In Rock Slope At Left Bank Of Jinping I Hydropower Station

The preliminary review for characteristics and parameters of the rock masses and rock mass quality has been implemented according to the collected information of regional geo-environment, geological conditions, supporting, monitoring and in situ tests, and has been compared with the early results of surveys of the Jinping I Project. Thus, on the basis of factors of the control action of all kinds of structure of the slope, it can be deduced that the boundary condition controls the deformation, stability and structure partition of the slope. Then, the mechanism and law of deformation response during large-scale excavation in so high rock slope of Jinping I, have studied and summarized by surveying the appearance of deformation and rupture, and analyzing results of the system monitoring at different depth or the key parts of the slope and the excavation numerical simulation using the SIGMA/W software. According to the foregoing analysis, the study content of left bank excavation slope’s deformation response mechanism of geological-mechanics model and deformation stability is as follows:(1) Regional geological environment of this area is relatively stable, and current tectonic stress field, generally in the NW direction, has been under the low confining pressure and low energy accumulation stage of strain energy, but the adjacent large active fault-Anling River Fracture-tend to reach a higher activity level and the edge of the recent potential unbroken zone of the fault is over the dam site area, so the influence of this claims our attention.(2) The basic engineering geological conditions, revealed during the excavation, are overall consistent with the results of earlier exploration. More exactly, slope body’s (dam abutment and above) structure condition and rock mass quality are of deviation, the rock mass conditions in lower part of the slope are relatively better.(3) According to the in-situ tests and the wave patterns of for rock mass in excavation period, the review and comparative study shows that the parameters of rock mass deformation and strength in preliminary suggestions, obtained in the left bank of the slope, is reasonable and reliable at all levels. Based on those results, the guiding principles for subsequent analysis of the numerical simulation and parameters selection are provided.(4) Slope body’s macrostructure distinctly controls the excavating deformation: the appearance of stronger displacements come from multi-point displacement meter and obviously cracks due to deformation in structure of cavern concentrator are mainly concentrated in the cracking rock masses at dam abutment, and the location of the anchor ergometer, showing increasing anchorage force, as well, often sited nearby the outcrop of master discontinuities of such as the lamprophyre dike (X), f42-9fault, etc.(5) Deformation response of excavation in mechanics include:unloading rebound, distinction rebound, topping-tensile, deep sliding-tensile fracture, etc. These visual phenomena of deformation are mainly developed inside the slope and rarely extend to the slope’s surface. According to this, the slope deformation is in adaptive adjusting range and there is no local signs of deterioration.(6) The results of system monitoring at different parts and depth of the slope, show that displacement vector is roughly parallel to the slope surface nearby the opening line, and the distance is about100mm. The surface’s deformation at berm is dominated by horizontal displacement component and vertical displacement is given priority to settlement. Deep deformation of slope are mainly concentrated at position of deep cracks in the back of lamprophyre dike(X), lateral displacement is about40mm. The simulation results show that the vertical deformation is settlement displacement as a whole. The dynamic state of deformation caused by excavation response of slope is sensitive to the process of excavation with obvious features in tendency to excavated surface, volatility, periodicity, synchronicity. After excavation, these deformations tend gradually to converge. The influence of excavation on the slope above is strong within100m range of elevation and relatively weak within200～300m.(7) According to the analysis for deformation phenomenon investigation, monitoring data, actual working condition, the concept mode of slope deformation under excavation can be overall summarized as a composite model, which includes the compression at the bottom of "anchored rock wall", the upper topping and ballooning-deep sliding tension, further analysis using numerical simulation shows that the model is able to connect each deformation phenomenon appearing at various parts of slope.(8) In conclusion, on the left bank rock high slope of Jinping I, excavation deformation under the "large-scale excavation plus strong supporting" conditions, controlled by such f42-9fault, etc, as the specific geological structure, is a response for adaptive adjustment. And, the basic background of deep deformation arisen in the slope focus on the function of structure controlling and stress adjustment. That is to say, the larger scale of f42-9fault itself, the deeper scope controlling deep deformation; moreover, the larger scale of excavation, the stronger for stress differentiation. Three layers of shear holes and "anchored rock wall" formed by anchor cables in itself is the basic control function of excavation deformation and stability of slope, the actual data confirm that this is a process.(9) Judging by the above several aspects, by the view of controlling deformation and stability of slope during construction, the implementation of support is adequate and the slope can be stable.