Authors: Shu Hong Wang, Juan Xia Zhang, Chun An Tang, Shan Yong Wang
Abstract: A series of numerical model tests were performed to investigate the behaviour of the
anisotropic rock surrounding circular excavations under high confining pressures. The aim was to
provide information on the formation of fractures and failure around deep level rock tunnels under
controlled conditions. Solid cubes containing a circular hole were confined to a vertical pressure with
same as the confinement in the horizontal directions. In this modeling, the inhomogeneous rock is
generated by using Weibull parameters which are related to the microstructural properties determined
by crack size distribution and grain size. The fracture angle is assumed to be 45o. The observed failure
zone around the excavation was simulated using both the maximum tensile strain criterion and
Mohr-Coulomb criterion respectively (as the damage threshold). And RFPA (Realistic Failure
Process Analysis) code was used as the calculating tool in this modelling, three opening modes are
simulated and compared. Computational model predictions that include crack propagation and failure
modes of rock show a good agreement with those of the observation in site. It is pointed out that the
damage evolution of EDZ strongly depends on the inhomogeneous, the excavation mode, anisotropic
property, and the various loading conditions. Concerning the existence of a weak plane, the amount of
displacement at the side wall of the tunnel was quite large, since the shear deformation occurred in
EDZ. The model is implemented in RFPA code and is able to represent the change in fracture patterns
between the solid and jointed parts. This provides confidence for the application of the numerical
model to the design of rock tunnels at great depth.
3014
Authors: Ming Tian Li, Shu Cai Li, Ning Zhang
Abstract: In order to understand the anchorage mechanisms the fracture behavior of jointed rock masses reinforced with rockbolts was compared with those of the jointed rock masses without rockbolts. Firstly the unaixal tensile tests were conducted on the specimens with inclined surface cracks, horizontal through cracks and horizontal a quarter through cracks to investigate the crack growth of the jointed rock masses without rockbolts. The experimental results show the fracture of the specimens without rockbolts belonged to tensile fracture in the catastrophic way under uniaxial tensile conditions. However the experimental results of the specimens reinforced with rockbolts show that rockolts can change the initiation of the pre-existing cracks, incur the secondary cracks and there existed stable crack propagation.
2562
Authors: Zhe Zhang, Yan Feng Feng, Qing Li, Shu Juan Zheng
Abstract: Based on the heterogeneity of rock, by using the RFPA2D, influene of the horizontal in-situ stresses on the distributions of plastic zones is discussed. Among the current problems that rock or civil engineers face, perhaps there is none as challenging as the characterization of fluid flow though fracturing rocks, especially when they are highly stressed. In mining and civil engineering projects, the re-distribution of the stress field during the excavation of tunnels and underground chambers lead to the formation of new fractures. These damages may cause dramatic changes in the permeability of the rock masses. As a result, the rate of water flowing into the tunnels and chambers will increase.
3377
Authors: Pei Feng Sun, Tian Hong Yang, Qing Lei Yu, Wei Shen
Abstract: With ShapeMetriX3D rock non-contact measuring technology, structural planes’ distribution of MiaoGou iron mine slope is got. Then, the Mont-Carlo method is used to create equivalent fracture network, with that scale effects and anisotropic properties of rock mass are studied by RFPA2D, considering different scales and directions in statistical window. The results show that both deformation modulus and the strength of the rock mass’s REV are 2.5 m. Furthermore, the strength ratio of filler to rock (K) and the strength of the rock mass fit the logarithmic relationship in rough, while the elastic modulus ratio of filler to rock (M) and the strength of the rock mass fit the linear relationship in rough. The strength of no joints rock mass is much stronger than three times of the strength of jointed rock mass, but the rock mass elastic modulus of no joints is less than 1.6 times of the elastic modulus of jointed rock mass. The research results are directive and have reference value for the study of anisotropy mechanical parameters of rock mass engineering.
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