DEM is now recognized as a powerful tool for simulating behaviors in rock mechanics. In particular, bonded particle model has been successfully applied in emulating the elastic modulus, Poisson's ratio and strength parameters of isotropic rock by controlling the microparameters in DEM model. In this study, the smooth joint contact model was introduced to represent the bedding planes in order to eventually model the transversely isotropic rock. Consideration of anisotropy is important for shale gas production because shale is shown to have a significant anisotropy in terms of elastic constants and compressive and tensile strengths. The chosen anisotropy model is transversely isotropic model which is believed to model the mechanical behavior of shale to a reasonable extent. The properties of Boryeong shale (Cho. et al., 2012) were used as a reference for transversely isotropic rock. Transversely isotropic rock model using DEM behaved in good agreement with the mechanical behaviors of Boryeong shale from the laboratory. The results can be evidence that development of anisotropic numerical model is promising through DEM. This anisotropic modelling is expected to pave the way for wide variety of engineering application ranging from traditional rock mechanics application to the emerging applications such as shale gas production.
Funatsu, Takahiro (National Institute of Advanced Industrial Science and Technology) | Takashi, Takehara (National Institute of Advanced Industrial Science and Technology) | Kuruppu, Mahinda (Curtin University of Technology)
The deformation and strength properties of rocks are often affected by internal structures of rock, such as bedding planes, microcracks, etc. These structures may cuase the mechanical anistorpy, and crack growth may be also affected the internal structures. In this study, we use the sedimentary rock sample having the bedding planes. There are two main aims in this study. The purposes of this research are:
1) To investigate relationship between fracture toughness and loading axis with respect to bedding planes.
2) To investigate relationship between fracture toughness and other mechanical properties of rock.
The mechanical properties investigated other than fracture toughness are uniaxial compressive strength, Young’s modulus, Poisson’s ratio and P-wave velocity. The experimental results indicate that Kimachi sandstone shows anisotropic properties of Young’s modulus, tensile strength and mode I fracture toughness, but little anisotropy of uniaxial compressive strength, Poisson’s ratio and P-wave velocity.
It is very difficult to predict weathering characteristics of rock because of limitation caused by time and space. An experimental study of accelerated weathering was performed on Cretaceous granitic rock samples from Jinhae and Gimhae area in southeastern Korea to investigate physico-mechanical property changes including revelation characteristics of microfractures due to laboratory accelerated weathering process. Total of 140 cycles of freeze-thaw were completed on deteriorated rock specimens with measuring the index properties as well as geometries of microfractures. Each complete cycle of freeze and thaw implemented 24 hours, comprising 2 hours of saturating in vacuum chamber, 8 hours of freezing at 16±1°C and 14 hours of thawing at room temperature. The seismic velocity was found to decrease with increasing freeze-thaw cycle. Effective porosity and absorption tend to increase with freeze-thaw cycle. The amount of deterioration of rock samples depend on pre-test degree of weathering. Effective porosity, absorption and seismic velocity can be used as the measure of physical weathering for granitic rocks of the study area. The size and plane density of the microfracture on rock specimens were obviously changed with increasing freeze-thaw weathering. The conducted research in this study has shown that accelerated weathering test has strong capability to capture the weathering characteristics of deteriorated rocks.
Design of rock structures and analysis of rock mass behavior demands a proper understanding of the influence of loading rate on the mechanical properties of rock mass. Many researchers considered the effects of dynamic loads on rock specimens through laboratory tests and numerical methods. Nevertheless, generalizing the intact rock behavior to the rock mass is the most important issue. In this paper, the rock mass behavior in dynamic loads is studied whilestrain rates ranges from 10-5 to 1031/s. The generalized Hoek-Brown rock criterion is used to demonstrate the rock mass behavior in several loading rates and strain rates. The database was obtained from the literature,includes uniaxial and triaxial loading of rock samples. Uniaxial compressive strength and deformability modulus of the rock mass is illustrated under different strain rates and confining pressures. The variation of rock mass properties is analyzed under dynamic loading furthermore GSI, m, s and D parameters. It was concluded that uniaxial compressive strength of the rock mass increased by increasing strain rates and dynamic loads. Indynamic triaxial loading it was observed that an increase in confining pressure, increased rock mass strength. The deformability modulus is as increase as rock mass strength in uniaxial and triaxial conditions.
Nakanishi, Tatsuro (Japan Atomic Energy Agency) | Tsuda, Hidenori (Japan Atomic Energy Agency) | Abumi, Kensyo (Obayashi Corporation) | Uyama, Masao (Obayashi Corporation) | Ohnishi, Yuzo (Kyoto University)