Thaya, S. (Tokyo Institute of Technology) | Pipatpongsa, T. (Tokyo Institute of Technology) | Takahashi, A. (Tokyo Institute of Technology) | Doncommul, P. (Electricity Generating Authority of Thailand)
The large deposits of freshwater snail fossils aging around 12-13 million years has been discovered at Mae Moh lignite mine in the northern part of Thailand. The preserved area of snail fossils with layers of up to 12 meters deep in the mining area has been set aside; however, there is a concern about the influence of mining activities in the vicinity area as well as excavations at a deeper depth. Therefore, detailed studies of the strength characteristics of snail fossils become necessary. The present study reported part of an investigation program in which direct shear strength properties of snail fossils were focused through the direct shear test with constant vertical stress under wet and dry conditions. The intact and disturbed samples were collected from a subsurface of a location deposited outside the preservation area. The effects of vertical effective stress, water, overconsolidation, and multi-reversal shearing on the shear strength properties of snail fossils were examined. The results show that the stress ratio decreases with increasing the vertical effective stress and the number of shearing. The presence of water appeared to have an impact on strength properties to some degrees. In addition, there is a rise in the stress ratio as the overconsolidation ratio increases.
ABSTRACT The object of this study is to investigate the unloading failure mechanism of hard rocks in the unloading process. A commercial finite element program LS-DYNA was employed to simulate the rock unloading process. The implicit and explicit methods were performed in sequence to simulate the static initialization-dynamic unloading process of rocks. The numerical results indicated that the rock failure can be induced by releasing of the initial stress, and the previous result of the equivalent initial stress release rate (EISRR) theory based on the 1D stress state is not suitable for 3D stress state. In 3D stress state, a new definition of equivalent strain energy release rate (ESERR) was introduced. The further study indicated that the ESERR can characterize the effect of different confining stresses and different unloading path on rock unloading. A significant finding is that the ESERR can quantitatively describe the characteristics of the unloading process under 3D stress state. This finding indicated that in practical underground excavation engineering, dynamically controlling the ESERR can be used to increase excavation potential of rocks and minimize the needed external excavation energy by using the initial energy.’
Leelasukseree, Cheowchan (Chiang Mai University) | Pipatpongsa, Thirapong (Tokyo Institute of Technology) | Khosravi, Mohammad Hossein (Tokyo Institute of Technology) | Mavong, Narongsak (Tokyo Institute of Technology)
For orthotropic materials, the value of tensile stress generating near the loading plate is influenced by contact area between loading plates and specimen in the diametrical compression test. However, very few studies on determination of contact area in diametrical compression test have been carried out. In this paper, the method of determination for contact area between loading plates and specimen in diametrical compression test is shown. For this method, the relation between the contact area and the ratio of tensile strain generating near the loading plate to that generating in the center of the specimen is calculated using theoretical solution and these results are shown in graphical representation. Furthtermore, this method is confirmed just befor failure for specimen that is made of mortar during experiments.
Nakanishi, Tatsuro (Japan Atomic Energy Agency) | Tsuda, Hidenori (Japan Atomic Energy Agency) | Abumi, Kensyo (Obayashi Corporation) | Uyama, Masao (Obayashi Corporation) | Ohnishi, Yuzo (Kyoto University)