DEVELOPMENT AND APPLICATIONS OF A HIGH- PERFORMANCE NUMERICAL METHOD FOR FLUID-SOIL- ROCK-STRUCTURE INTERACTION ANALYSIS BASED ON SPH AND DDA

九州大学学術情報リポジトリ

Kyushu University Institutional Repository

DEVELOPMENT AND APPLICATIONS OF A HIGH-

PERFORMANCE NUMERICAL METHOD FOR FLUID-SOIL- ROCK-STRUCTURE INTERACTION ANALYSIS BASED ON SPH AND DDA

彭, 新艶

http://hdl.handle.net/2324/4110493

出版情報：九州大学, 2020, 博士（工学）, 課程博士 バージョン：

権利関係：Statement of depositing dissertation and fulltext file have not been submitted.

（様式２）

氏 名 ：彭 新艶

論 文 名 ：DEVELOPMENT AND APPLICATIONS OF A HIGH-PERFORMANCE

NUMERICAL METHOD FOR FLUID-SOIL-ROCK-STRUCTURE INTERACTION ANALYSIS BASED ON SPH AND DDA

(SPH

DDA

区 分 ：甲

論 文 内 容 の 要 旨

Multiphase problems, e.g. problems related to fluid-solid or soil-rock-structure interaction, widely exist in geotechnical engineering. For example, soil-rock-mixture (SRM) landslides, which can cause serious disasters to human society, involve soil-rock-structure interaction. Tunnel water inrush phenomenon, which frequently occurred in tunnel construction process and can deteriorate the operating environment and even cause casualties, involves water-rock interaction. In order to conduct practical prediction and take preventive measures for disaster mitigation, it is necessary and important to analyze such kind of multiphase problems.

However, there is no effective numerical method currently for this purpose.

With rapid development of computer technology, numerical methods have become increasingly popular and gained wide acceptance in their capabilities of solving engineering problems. Among them, discontinuous deformation analysis (DDA) is a powerful technique in modelling the mechanical behavior of solid blocks such as rocks and structures. Meanwhile, smoothed particle hydrodynamics (SPH) demonstrates promising capability in simulating fluid dynamic system based on particles. Also, there are studies on the coupling of DDA and SPH for solving fluid-solid interaction problems. Although large advancement has been achieved in numerical simulation studies up to now, the following issues still remain unsolved: (1) how to develop a high-performance DDA program for large scale simulations by taking the advantage of multiple cores, which is almost standard configuration in a personal computer (PC); (2) how to develop a soil-particle based high-performance SPH program for the mechanical analysis of soil materials; (3) how to develop a comprehensive simulation program for analyzing fluid-soil-rock-structure interaction problems.

This study aims at to develop a high-performance numerical method for fluid-soil-rock-structure interaction analysis by coupling DDA and SPH and apply the developed method to analyze practical problems such as SRM landslide and tunnel water inrush hazard in geotechnical engineering. At first, a high-speed DDA program is developed by using CPU (central processing unit) parallel computing tec hniques based on OpenMP (open multi-processing) parallelization. It can speed up a large-scale 3-D DDA simulation 5 times faster than the original DDA program. And then, a soil-particle-based SPH program SPH_s is developed by implementing an existing elastic-plastic soil constitutive model associated with the Drucker-Prager yield criterion using GPU (graphics processing unit) parallel computing techniq ues. Thirdly, a new coupling program between the CPU parallel DDA and GPU parallel SPH_s is developed based on a penalty method using the Mohr-Coulomb failure criterion. It can be applied to simulate soil-rock-structure interaction phenomena. Finally, the developed high-performance method is successfully applied to study the mechanical behaviors of SRM landslides and tunnel water inrush problems.

The contents of the thesis are organized as follows:

Chapter 1 introduces the background, the scope and objectives of this study, and the organization of

the thesis. The SRM landslide disasters and tunnel water inrush problems are briefly introduced. The methodologies for such problems are reviewed. The above-mentioned unsolved issues of the current studies are then presented.

Chapter 2 develops a high-speed DDA program for large-scale simulations. Following the review of fundamentals of DDA together with its advancements and applications, the advantages of DDA for modelling the mechanical behaviors of rocks and structures and the difficulty in large -scale simulation are discussed. Unlike SPH of explicit method, GPU parallel computing techniques are not very suitable for DDA of implicit method. With the advancement of PC, multi-core CPU becomes popular. Thus, a parallel DDA program is developed using CPU parallel computing techniques based on OpenMP para llelization theory. It has been shown that as large as 5 times speedup from the original program is available by using a 6 -core PC for simulating a large-scale model with 1371 blocks, which is very useful in practical applications of DDA.

Chapter 3 develops a soil-particle based SPH program called SPH_s using GPU parallel computing techniques. Following the review of fundamental theory, the advancement of progra mming and applications of SPH, the advantages of SPH for modelling fluid dynamics are discussed . In order to couple with CPU parallel DDA, the soil-particle GPU parallel SPH program with an expected soil constitutive model is needed in this study, but there are no existing codes available for this purpose. Thus, the program of SPH_s based on GPU is developed by implementing an existing elastic-plastic soil constitutive model associated with the Drucker-Prager yield criterion. The correctness and accuracy of SPH_s is verified by simulating a dam-break test of soil column. The calculated results such as large deformations and post-failure behavior of the soil material are in good agreement with those from the laboratory test.

Chapter 4 develops a new coupling program, called DDA-SPH_s, between the CPU parallel DDA and the GPU parallel SPH_s for simulating soil-rock-structure interaction phenomena. Following the review on the boundary treatment of SPH based on virtual or ghost particles, and boundary treatment of the existing DDA-SPH coupling program taking DDA blocks as moving boundaries, the existing DDA and SPH coupling scheme is clarified inapplicable to DDA-SPH_s because the strength from the contact between a soil particle and a rock block should be considered. Thus, a new coupling scheme bridging DDA and SPH _s is proposed based on a penalty method using the Mohr-Coulomb failure criterion. The contact between block and particle is treated as a vertex-to-edge/face contact. Contact forces between SPH particles and DDA blocks are calculated based on the penalty method. The Mohr-Coulomb failure criterion is used for separating or coupling behavior of a pair of soil particle and block. The correctness and accuracy of DDA -SPH_s is verified by reproducing the failure process of a modular-block retaining wall system conducted in an experiment. The calculated results are in good agreement with those measured from the experiment.

Chapter 5 presents practical applications of the DDA-SPH_s method to study the mechanical behaviors of SRM slopes which widely exist worldwide and can lead to landslides cau sing serious damages to the infrastructures and endanger human lives. Previous studies majorly focus on either rock slope or soil slope but very few for the mixture of both. It is obvious that the mechanical behaviors of a n SRM slope are affected by different shape, size and content of rocks and their distribution in a slope. Thus, a number of simulations with soil-rock-mixture slope models are carried out. The results show that the deformation is proportional to the roundness but inversely proportional to the sorting coefficient of rock blocks. Also, the deformation of an SRM slope with rocks distributed along the potential sliding surface is much smaller than that with rocks distributed in the sliding body. In addition, the runout distance of a n SRM landslide and the maximum impact force on nearby buildings increase with higher rock contents, which is more destructive to nearby structures and human lives.

Chapter 6 simulates tunnel water inrush phenomenon using the coupling program between the parallel DDA and water-particle based SPH. It is the first time that a tunnel water inrush phenomenon is reproduced and the mechanical behaviors of tunnels are clarified from the viewpoint of the distance T from the tunnel face to the water domain, the water quantity, and the presence or absence of water outlet. The results show that (1) the deformation of tunnel increases with either the decreasing of T or increasing of water pressure induced by the initial height of water domain; (2) the deformation of tunnel is small er without water outlet and slightly affected by the location of a water outlet.

Chapter 7 summarizes the conclusions of the study and proposes recommendations for future research .