Research On Technique And Application In Refined Analysis Of Complicated Geotechnical Engineering Structures Based On Scaled Boundary Finite Element Method

In order to promote the transformation of clean and low-carbon energy sources and accelerate the development goal of non-fossil energy proportion,China has proposed to plan ahead the development layout of clean energy such as hydropower.A number of large geotechnical structures such as high earth-rock dams have planned and started construction in Southwest and Northwest China.However,the area is located in active seismic zone with frequent strong earthquakes and strong potential damage to the structures.The damage of high dams caused by earthquakes will produce incalculable consequences and secondary disasters,which seriously threaten the safety of national life and property and regional economic development,making the seismic safety of high earth-rock dams and other geotechnical structures particularly prominent.Therefore,it is of great theoretical and engineering significance to ensure the smooth operation of the project and carry out seismic safety performance evaluation research.Fine analysis can further improve the rationality and accuracy of analysis,which is the inevitable trend of numerical simulation in domestic and overseas.However,at present,there is almost no research on fine simulation and analysis of large geotechnical structures such as high earth-rock dams,mainly because of the complexities of such geotechnical engineering structure,and the interaction between structure and infinite foundation,as well as the interaction between materials and interfaces are needed to be considered at the same time.In addition,such geotechnical structure are huge in volume(usually over 100 meters in height,over 1 kilometer in length and width),but at the same time,there are some key small-scale components(minimum thickness is about 0.3 m),such as impervious panels and impervious walls,leading to the scale of the structure itself varies greatly(100 to 1000 times),which makes it difficult to efficiently establish fine analysis grids and carry out large-scale solution analysis using the traditional technology.Therefore,it is of great research significance and engineering application value to establish an efficient cross-scale fine computing model and to develop a high-performance cross-scale fine analysis method,which can accurately describe and track the damage and failure process of key structural components.This paper combines with the national key R&D plan"Research on damage evolution mechanism and safety evaluation criteria of multi-coupling system of super-high earth-rock dam under strong earthquake";National Natural Science Foundation of China"Research on deformation characteristics of rockfill materials and ultimate seismic capacity of high rockfill dam under extreme earthquake load"and Research on important water conservancy and hydropower projects,such as research on numerical simulation of RuMei core-wall rockfill dam,considering the interaction of dam-foundation-reservoir water system,the three-dimensional non-linear static and dynamic fine analysis of Dashixia concrete face rockfill dam and the special study on Xinjiang Altash concrete face rockfill dam.Based on the theory of Scaled Boundary Finite Element Method(SBFEM),the following work has been carried out to solve the problems of static-dynamic analysis and seismic safety evaluation of large geotechnical-structural structures,such as cross-scale,refinement and high efficiency.(1)Using efficient quad-tree and octree discretization technology,a series of processing procedures,such as format conversion and sorting,are developed.A pre-processing mode are achieved with the advantages that are easy to operate,low labor cost and easy to modify and regenerate.The grid cross-scale,refined and efficient discretization problems suffered from large-scale complex geotechnical engineering structures can be solved.(2)The polyhedron boundary surface element is interpolated by the polygon mean function,and the semi-analytical shape function and stiffness of the element are derived from SBFEM elasticity theory.An improved three-dimensional scaled boundary complex polyhedron element is developed.This method can directly solve the octree polyhedrons and other complex polyhedral elements which is difficult to calculate directly by the traditional method.The presented method improves the flexibility,versatility and robustness of the finite element method.The large-scale cross-scale fine analysis of engineering structures is achieved.(3)Firstly,the element shape function and strain-displacement matrix are constructed using boundary Gauss integral points and constant elasticity modulus.Then,based on the traditional FEM framework,the conformity matrix,stiffiness matrix and stress integral are solved by introducing in-domain integration points.In this manner,the scaled boundary two-dimensional polygon and three-dimensional polyhedron elements are developed for elasto-plastic analysis.This work breaks through the limitation that traditional SBFEM is mainly built for elastic analysis,and provides a simple and efficient solution for the non-linearization of SBFEM.(4)Combining the mean-vaule polygon interpolation and theory of interface element,the spatial polygon three-dimensional interface element is developed.The problem that traditional Goodman element is difficult to solve the polyhedron interface element can be resolved well.Conjunction with the aforementioned work,a cross-scale fine analysis method for all systems considering infinite foundation-soil-interface-structure interaction is established.(5)The common attributes of SBFEM and FEM element construction are abstracted using object-oriented design method and element encapsulation technology.And the program development interface of two numerical analysis methods is unified.Then the developed numerical algorithms are integrated in the GEODYNA finite element program platform developed by the research group,making the seamless coupled calculation of SBFEM-FEM achieved.Additionally,according to the geometric similarity of cubic elements generated from octree,an efficient nonlinear similar elements acceleration technique is developed.The solution efficiency of large-scale elastic-plastic fine analysis is significantly improved.A high-efficiency cross-scale fine analysis system for large-scale and complex geotechnical engineering is developed and applied to the fine seismic safety evaluation of more than ten maj or hydroelectric and nuclear proj ects,such as the RuMei core wall dam(the world’s highest,315m),Dashixia face-slab dam(the highest under construction,247m),and SanAo nuclear power plant.The method has also achieved good application results in the cross-scale fine damage analysis of subway structures,which has a good application prospect.