Browsing by Author "Fukuda, D"

Now showing 1 - 7 of 7

item: Conference-Abstract
Development of a numerical simulation method for complex fracture process of rocks based on 3-D ECZM-FDEM using GPGPU parallel computation
(Division of Sustainable Resources Engineering, Hokkaido University, Japan, 2024) Takarada, K; Fukuda, D; Di, W; Liu, H; Ogata, S; Maeda, Y; Min, G; Kawasaki, S; Iresha, H; Elakneswaran, Y; Dassanayake, A; Jayawardena, C
For the developments of surface and underground mines, numerical simulation has been regarded as a highly crucial approach in terms of mining design and safety. The combined finite-discrete element method (FDEM)[1] has attracted significant attention for reasonably simulating very complex fracture processes of rocks. FDEM is based on the continuum mechanics model considering finite-strain theory, the cohesive zone model (CZM)[2] by utilizing initially zero-thickness cohesive elements (CEs) and potential-based contact mechanics model. The FDEM based on the intrinsic CZM (ICZM), which inserts the CEs at the onset of the simulation, has been the mainstream of previous studies applying FDEM due to its simpler implementation. Although the FDEM is generally known as a computationally expensive numerical method for both two-dimensional (2D) and three-dimensional (3D) problems, the computational acceleration of the ICZM-based FDEM can be achieved with relative ease through parallel computation using general-purpose graphics processing units (GPGPUs). However, the accuracy of continuous deformation when rock is intact is significantly compromised in the ICZM. The FDEM based on the extrinsic CZM (ECZM), which activates CEs only when and where the local stress reaches the given activation criteria, is expected to overcome this issue. However, although the implementation of 2-D ECZM-based FDEM with the GPGPU parallel computation has been reported, its 3-D counterpart has not been achieved. Based on this background, this study proposes a novel master-slave algorithm to achieve the implementation of the GPGPU-parallelized 3-D ECZM-based FDEM. Figure 1 shows the examples results of GPGPU-parallelized 3-D ECZM-based FDEM for uniaxial compression test simulation and spalling test simulation [3]. These results indicate that the developed ECZM-FDEM can reasonably reproduce the fracture and failure patterns of rocks in both static and dynamic tests compared to laboratory tests. The significant advantage of the proposed approach lies in the fact that the precision of continuous deformation can compared to those of the parallelized ICZM-based FDEM. The proposed approach could be an important basis for the further developments of the ECZM-based 3-D FDEM for simulating very complex 3-D rock fracturing processes in the various rock engineering problems.
item: Conference-Full-text
Experimental and numerical analysis of dynamic fracture processes in rock and rock-like materials using NRC vapor pressure agent
(Division of Sustainable Resources Engineering, Hokkaido University, Japan, 2024) Min, G; Fukuda, D; Di, W.; Liu, H; Kawasaki, S; Cho, S; Iresha, H; Elakneswaran, Y; Dassanayake, A; Jayawardena, C
This study investigates the fracture characteristics of rocks and rock-like materials subjected to the Nonex Rock Cracker (NRC), a vapor pressure crushing agent. The NRC generates vapor pressure by instantaneously vaporizing a crystallized water mixture through the thermite reaction. Both experimental methods, using high-speed cameras and dynamic pressure gauges on Polymethyl methacrylate (PMMA) and granite blocks, and numerical simulations with a 3-D combined finite-discrete element method (FDEM) were utilized. Results indicate that gas pressure infiltrating pre-existing cracks primarily drives crack propagation. The study concludes that accurately modeling gas injection into initiated cracks during deflagration is essential for reasonable numerical simulations of rock fracturing processes using NRC.
item: Conference-Full-text
Numerical analysis of effects of clay on a cut rock slope deformation at an open-pit limestone mine, Japan
(Department of Earth Resources Engineering, University of Moratuwa, 2021-12) Amagu, AC; Zhang, C; Kodama, J; Iwasaki, H; Ikegami, S; Sainoki, A; Fukuda, D; Fujii, Y; Dissanayake, DMDOK; Jayawardena, CL
Rock slope instability is one of the major challenges of rock engineering projects, including open-pit mining. In this regard, rock slope deformation due to excavation, change in temperature, and influence of rainfall and snowfall have been previously investigated to understand characteristics and causes of slope deformation observed at an open-pit limestone quarry in Japan. The results only revealed characteristics of the deformation as forward and downward displacement of the cut rock slope, but its causes were not clarified. To deduce the causes of the rock slope deformation, we employed the 2-dimensional finite element method (2-D FEM) to investigate the deterioration effect of clay found at the footwall of the rock slope in terms of reduction in Young's modulus of the clay based on experimental results. Firstly, change in distances was analysed from displacement data measured by the automated polar system (APS) over five years, which decreases gradually with time. Secondly, the simulation results were discussed and then compared with the measured displacement data, which shows similar tendencies at the middle and top of the rock slope revealing maximum displacement at the middle of the rock slope. Conclusively, deterioration of clay at the footwall of the rock slope is one of the possible causes of the deformation in the quarry.
item: Conference Full-text
Prevention of catastrophic volcanic eruptions
Fujii, Y; Fukuda, D; Dassanayake, ABN; Abeysinghe, AMKB; Dassanayake, ABN; Elakneswaran, Y
Giant volcanic eruptions emit sulphate aerosols as well as volcanic ash. Needless to say that volcanic ash causes significant damage to the environment and human at large. However, the aerosols are even worse. They reach the Stratosphere and stay there for months to years reflecting insolation. As a result, air temperature at the Earth's surfaces drops. Even a slight temperature drop may cause severe food shortage. Yellowstone supervolcano, for example, can even make human in the Northern Hemisphere extinct in several hundred thousand years. Therefore, gradual energy release by supercritical geothermal power generation was proposed to prevent such catastrophic eruptions. The necessary technical innovation is drilling into the depth. However, after the innovation, the power generation itself would be profitable. The risk is unpredicted induction of unwanted catastrophic eruptions.
item: Article-Full-text
Tangent modulus method – An original method to measure in-situ rock stress
(Elsevier, 2018) Fujii, Y; Makasi, M; Kodama, J; Fukuda, D; Goto, K; Kumakura, S; Kanaoka, M; Dassanayake, ABN
This paper proposed Tangent Modulus Method (TMM) which is an improved oriented core method to determine in-situ rock stresses. In this approach, the cylindrical specimens prepared along different directions from thick core samples were uniaxially compressed twice to a given stress level. The stress value of the bending point in the first loading cycle of the stress-tangent modulus curve is considered as the normal component of the in-situ rock stress along the drilled direction of the specimen. Four types of rocks from soft porous tuff and sandstone to hard crystalline granite was investigated to evaluate the potential of this method. The effects of changes in strain rate, temperature, water content, confining and pore pressure, and stresses larger than the preload on the stress value of the bending point were experimentally investigated on preload specimens to investigate their influence on TMM. Comparison of the stress measurement results by TMM and an overcoring method at AK tunnel in Hokkaido, Japan was also performed to validate the TMM.
item: Article-Full-text
A Three-dimensional constitutive model for rocks based on a strain-dependent elastic modulus
(The Geological Society of America, 2022) Li, Z; Fujii, Y; Kodama, J; Fukuda, D; Dassanayake, ABN; Sinkala, P
Our research group previously proposed a simple two-dimensional (2D) constitutive model for rocks to simulate not only the axial stress–axial strain relationship, but also the axial stress–lateral strain relationship, with few complicated equations. However, the failure envelope that it predicted was linear, and it did not consider the effect of the intermediate principal stress (⁠σ2 ⁠). In the present study, the authors modify this simple 2D model to have a convex failure criterion. Then, the model is extended to a simple three-dimensional (3D) model that well approximates true triaxial stress–strain curves for real rocks under specific values of σ2 and σ3 and uses only four parameters. However, the predicted peak stress–σ2 relationship is linear. Finally, a modified 3D model was developed, which exhibited the true triaxial convex failure criterion. The equations in this model are simpler than the conventional true triaxial failure criteria. The proposed models can be implemented with a finite element method to improve the design of rock structures.
item: Article-Full-text
Water drainage from Kushiro Coal Mine decreased on the day of all M ≥ 7.5 earthquakes and increased thereafter
(Nature Publishing Group, 2018) Fujii, Y; Ichihara, Y; Matsumoto, H; Kodama, J; Fukuda, D; Dassanayake, ABN
The amount of water drainage from Kushiro Coal Mine in Hokkaido, Japan decreased on the day of all M ≥ 7.5 earthquakes with epicenters within 300 km of the mine during the monitoring period and increased after these earthquakes. This is a valuable finding which would give us a clue to understand pre- and post-seismic rockmass behaviors and contribute for progress in earthquake prediction in future.