Yuzo Ohnishi

Development of high‐order manifold method

The Manifold Method of Material Analysis (MM) with high-order displacement functions has been derived based on triangular meshes for the requirement of high accurate calculations from practical applications. The matrices of equilibrium equations for the second-order MM have been given in detail for program coding. The derivation of the method is made by means of approximation theory and very few new mathematical concepts are used in this paper. So, it may be understood by most engineering researchers. By close comparison with widely used Finite Element Method, the advantages of MM can be seen very clearly in the following aspects: (1) the capability of processing large deformation and handing discontinuities like block oriented Discontinuous Deformation Analysis method; (2) making element meshes easily and (3) using high-order displacement functions easily. The C program codes for the second-order MM has been developed, and it has been applied to the example of a beam bending under a central point loading. The calculated results are quite good in agreement with theoretical solutions. By contrast, the results calculated for the same model by use of the original first-order MM are far from the theoretical solutions. Therefore, it is important and necessary to develop high-order Manifold Method for the complicated deformation problems.

Hydro-mechanical response of a fractured granitic rock mass to excavation of a test pit — the Kamaishi Mine experiment in Japan

A thermo-hydro-mechanical experiment was conducted in a fractured granitic rock mass at the Kamaishi Mine in Japan. The experiment consists of the excavation of a cylindrical test pit on the floor of an experimental drift. The test pit was then filled with bentonite with an embedded heater. During the excavation of the test pit, the hydro-mechanical response of the surrounding rock was monitored. This paper presents the efforts of four research teams to numerically simulate the hydro-mechanical response of the rock mass during excavation. While the total inflow rate to the test pit, the flow distribution on the pit walls and the displacements in the rock mass away from the pit could be reasonably predicted, the pore pressure in individual boreholes, and the expansion behaviour of the pit were less successfully simulated. The reasons for these discrepancies are discussed in the paper.

Practical studies on rockfall simulation by DDA

Abstract In this paper, simulations of real rockfall by discontinuous deformation analysis (DDA) are conducted. In the simulations, the energy losses of rockfall are categorized into three types, i.e. the loss by friction, the loss by collision, and the loss by vegetation. Modeling of the energy loss using absolute parameters is conducted by the DDA method. Moreover, in order to verify the applicability and validity of the proposed DDA, field tests on rockfall and corresponding simulations of rockfall tests by DDA are performed. The simulated results of rockfall velocity and rockfall jumping height agree well with those obtained from the field tests. Therefore, the new technique properly considers the energy-absorption ability of slope based on vegetation condition and shape of the rockfall, and provides a new method for the assessment and preventive design of rockfall.

A study on problems associated with finite element excavation analysis by the stress‐flow coupled method

This study attempts to address some problems associated with excavation analysis by means of the stress-flow coupled method. This is done through the investigation of two examples, both of which are excavation analyses modelling a sequential excavation process. The first example is a three-dimensional elastic analysis of a tunnel constructed in soft rock layer. The second example is an axi-symmetric elasto-plastic analysis of a shaft constructed in slightly overconsolidated clay layer. In order to clarify the effect of sequential excavation process on the analysis results, a conventional two-dimensional analysis on each example is also carried out. Through this study, we will demonstrate that it is essential to consider in detail the incremental advance of a tunnel face when one investigates the change of pore water pressure and stresses surrounding a tunnel face during excavation. Additionally, on the basis of the analytical results obtained, a proposal is presented for evaluating the stability of rock mass surrounding a tunnel during construction.

7 – Thermal–Hydraulic–Mechanical Coupling Analysis of Rock Mass

Publisher Summary This chapter describes methods for the analysis of coupled thermal, hydraulic, and mechanical phenomena of rock mass. The prediction of the phenomena is most important for the plan and design of a structure constructed in a rock mass. For coupled thermal and mechanical problems, there are many examples in which classical continuum mechanics are applied with numerical calculation techniques. In such cases, the medium is often considered as elastic. When plastic deformation because of thermal stress is considered, the yield function is needed as a function of temperature in addition to stress. When a repository is constructed in saturated deep crystalline rock, convection of the groundwater induced by increasing temperatures is the most important matter for assessment. As groundwater does not homogeneously fill the volume of a fractured rock, the effect of groundwater on the deformation behavior can be anisotropic. When fracture flow is considered as a phenomenon restricted to a plane, the effect of the deformation on the permeability is considered as a change in the area of the channels in the fracture plane.

STABILITY ANALYSES FOR ANCIENT MASONRY STRUCTURES USING DISCONTINUOUS DEFORMATION ANALYSIS AND NUMERICAL MANIFOLD METHOD

In this paper, the stability including stress distribution of two ancient masonry structures, the pyramid of the Pharaoh Khufu, Egypt and the Pont of Gard, were analyzed using discontinuous deformation analysis (DDA) and numerical manifold method (NMM). For the simulation using NMM, the newly developed four-node isoparametric element was used. The stress distributions/concentration were calculated and compared between the two methods. The calculated results show qualitative agreement with observations. DDA and NMM are applicable to simulate the physical phenomena of masonry structures.

THM Simulation of the Full-Scale In-Situ Engineered Barrier System Experiment in Grimsel Test Site in Switzerland

Abstract Coupled THM simulation of the FEBEX, which is the full-scale in-situ Engineered Barrier System Experiment performed in Grimsel Test Site in Switzerland, is one Task in the international cooperation project DECOVALEX III. In the Task, the simulation of the thermal, hydraulic and mechanical behaviour in the buffer during heating phase is required, e.g. the evolutions and the distributions of stress, relative humidity and temperature at the specified points in bentonite buffer material. This report presents our approach for calculation of the Task. Our numerical code THAMES is the three-dimensional finite element simulator of fully coupled processes. First, we defined the input data for THAMES from the supplied properties of FEBEX bentonite. After calibrations of some parameters such as thermal vapour diffusivity, the analysis that treats fully coupled thermal, hydraulic and mechanical processes was carried out.

A numerical study on the effect of shear resistance on the landslide by Discontinuous Deformation Analysis (DDA)

Japan is located in Circum-Pacific earthquake zone, which is one of the most seismologically active areas in the world. As a result, landslides have occurred frequently and often cause serious damage not only to human lives but also to the various important structures such as national roads, railway, electric power plans etc. From the engineering point of view, to investigate the mechanism of landslide due to earthquakes and estimate the damage caused by landslides are important issues. In this study, as the first step, to check the validity of DDA simulation for the seismic problems, a series of shaking table tests were carried out in the laboratory and simulated by DDA. Then, one of the largest landslides occurred in Aratozawa Area, Miyagi, Japan in 2008 caused by Iwate-Miyagi Nairiku Earthquake was simulated using DDA and discussed the mechanisms of the landslide. The 2-D DDA model for one of the survey lines was created based on the geological survey, and physical properties were determined from the laboratory tests using rock/soil samples obtained from the landslide site. In this study, to discuss the mechanism of the landslide, a series of parametric study in terms of shear resistance along the fractures was conducted.

Application of Manifold Method (MM) to the stability problems for cut slopes along the national roads

Recently one of the most challenging problems for civil engineers is how to construct new structures/infrastructures adjacent pre-existing ones and how to evaluate the effect of the new construction on the pre-existing structures (so-called neighbouring construction). The Manifold Method (MM) is one of the discontinuum based numerical approaches to simulate the mechanical behaviour of fractured rock masses including large deformation/displacement along fractures as well as stress/strain conditions of the rock blocks/masses. In this study, the MM was used to investigate the stability of the cut slope in the highly fractured rock masses along one of the national roads in Japan, focusing on the effects of new construction on the pre-existing structures/infrastructures. The effect of reinforcement during the construction such as rock bolts, anchors, etc. was also investigated and evaluated quantitatively by numerical simulations using MM.

Numerical Analysis of Discontinuous Rock Masses Using Three-Dimensional Discontinuous Deformation Analysis (3D DDA)

Numerical analysis methods are considered very important in the field of geotechnical engineering, particularly in the area of disaster prevention. Discontinuous Deformation Analysis (DDA) is a type of discontinuous numerical analysis method that is frequently used in this topic. Since most geotechnical engineering problems are three-dimensional, Two-Dimensional Discontinuous Deformation Analysis (2D DDA) computations have exhibited limited accuracy. In order to simulate three-dimensional block behavior more accurately, the Three-Dimensional Discontinuous Deformation Analysis (3D DDA) theory for blocks with general shape was developed. This paper describes the basic principles of 3D DDA, and goes a step further by developing a new 3D DDA method. This new 3D DDA method proposed by authors is applied to an actual example site. In order to demonstrate the capability of this new method in the numerical analysis of discontinuous rock masses, the simulation results were compared and examined with the actual monitoring of the displacement behavior proceeding that led to the failure at the field site. The results show the applicability of 3D DDA in determining the deformation and failure mechanisms of rock masses.