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.
In-situ stresses are one of the most important elements for the design and stability assessment of rock engineering structures and earthquake science. Many in-situ stress inference and measurements techniques are devised and they are broadly classified into direct or indirect techniques. Drilling and blasting technique is widely used as an excavation technique in rock engineering practice. The experiments on specimens clearly indicated that the fracture zones around the blasthole was larger in the direction of the maximum load. Some parts of the blastholes remain following blasting. The author proposes a method how to infer the in-situ stresses from the damage zones around the blastholes in this article and it is named as the blasthole-damage method. The fundamentals of this method are described and it is applied to several sites where in-situ stress states are obtained by using direct or other indirect techniques. The inferences are compared with measurements and the validity of the method are discussed in view of the measurements or inferences from other methods.