Study On Excavation Stability Of Complex Rock Slope At High Field Stress Areas

The problem of excavation stability on complex rock slope is frequently encounted in the course of hydropower engineering construction. Thus, this paper will concentrate on the above topic based on the project-JinPing I stage hydropower station-the highest arch dam in the world. Started from the analysis of geological survey in engineering, the concept, classifications as well as the corresponding failure modes of the slope structure of complex rock slope are summarized in areas with high field stress. The field in-situ stress of dam area is inversed with regressive analysis method according to the actual measurement results toward several points. And on the basis the applied method from regressive ground stress to calculation model is studied. Furthermore, the release rules of ground stress caused by slope excavation are analyzed. And the corresponding secondary stress divisions are made by using qualitative and quantitative method. Hereby the condsideration of ground stress in the slope stability is analyzed. Then based on damage mechanics theory and rock empirical strength criterion, new statistical damage constitutive model of rock is derived. By using its strength reduction principle, the numerical simulation method considering regressive ground stress and three-dimensional point safety factor method based on deformation-stress field are put forward to evaluate the excavation stability of slope. As for block combinations including multi-group transfixion structure surface in the slope mass, corresponding calculation program is compiled by using block theory. Finally, three-dimensional monitoring feedback analysis is made by field monitoring results. While theoretical research is made, the application of the theory to practical engineering and checks for the legitimacy of the theoretical results compared with practice are important part in this thesis. The following is the research contents.(1) The determination about concept, types and its corresponding instability failure mode of slope mass structure of complex rock slop at high field stress areas. Compared with rock mass structure and slope structure, the concept of slope mass structure is put forward at high field stress areas. Based on the summarization of deformation and failure mode and instability mechanism, slope mass structure is divided into six large classes. And subclass is made to this slope mass structure commonly developed 1-3 group joints in slope mass. The method of the stability analysis of complex rock slope based on slope mass structure is preliminary established.(2) The regression of initial stress field considering cutting valley and wastage. The influence factors of ground stress and special factors of cutting valley and wastage at deep-incised valley areas are analyzed. According to actual measured point stress and using multivariate linear regression analysis, the field stress which can be used in engineering is gained. The distribution regular of gound stress field at deep-incised valley areas is summarized. The precise method of stress field from regression to calculation model is built.(3) The analysis of secondary stress adjustment caused by slope excavation and the consideration of tectonic stress in slope stability analysis. By analyzing releasing characteristic of groud stress caused by slope excavation, the zones of secondary stress are analyzed from qualitative and quantitative two sides. On the basis, the consideration of ground stress in slope excavation stability is analyzed.(4) The numerical simulation method considering regressive initial stress in slope excavation stability analysis. According to the method which is put forward in the first and second, the calculation model is built and the initial ground stress in model is defined. Based on damage mechanics and the empirical strength criterion of rock failure, by the laboratory test of rock physical mechanics properties, new rock damage constitutive model and damage evolution equation are derived. Taking FLAC3D as development platform and using its embedded FISH language, the data interface program is compiled. The damage evolvement process of rock failure is reflected in numerical calculation. So the potential failure surface of slope is defined. On the basis, the three-dimensional point safety factor method based on deformation-stress field is put forward to evaluate the excavation stability of slope.(5) The three-dimensional block stability analysis program of rock slope based on block theory is compiled. As to the block combination including multi-group transfixion structure in slope mass, according to the basic knowledge of block theory, three-dimensional block stability analysis program is compiled by using programming language. The problem of the determination of potential instability block formed by muti-group structure surface combination is solved, especially in the semi-deterministic blocks and random block.(6) Three-dimensional monitoring feedback analysis of slope. On the basis of the gained geological data and test of rock physical mechanics properties, according to practical situation of the computational domain, the range of waiting for inversion parameters is determined, design scheme of numerical simulation by using orthogonal test, and the displacement of every scheme corresponding monitoring point is calculated by FLAC3D. In accordance to the functional relationship (scilicet degree of closeness) between the displacement of slope monitoring point and the corresponding calculated value of every scheme, the optimum calculation parameters complying with the range of calculation model and boundary is determined. Finally, the face analysis of excavation deformation is done by the result of parameter inversion, which can provide corresponding reference to numerical calculation and block stability analysis.