Rock Mechanics
Weiqun Liu; Tian Fang; Sheng Sang
Abstract
Mudstone is a common rock in underground engineering, and mudstone with fractures, have the certain self-closing capability. In this paper, we employed experiments and numerical analyses to investigate the mechanism of such a characteristic, and also examined the permeability pattern of mudstone overburdens. ...
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Mudstone is a common rock in underground engineering, and mudstone with fractures, have the certain self-closing capability. In this paper, we employed experiments and numerical analyses to investigate the mechanism of such a characteristic, and also examined the permeability pattern of mudstone overburdens. The experiments were performed with the MTS815.02 testing system, involving material properties under different water contents and their crack-closing behaviors. The principal task of numerical analysis is to determine the permeability of fractured mudstone layers, working with the COMSOL platform. The experimental results show that the Young’s Modulus of water-saturated mudstone is just 2.2% of that of natural mudstone, and the saturated also exhibit a remarkably obvious creep behavior. As the surrounding pressures increase, the permeability coefficient of fractured mudstone decrease exponentially, even dropping by two orders of magnitude corresponding to over 2.0MPa pressures. Based on these experiment outcomes, we can easily infer that rapid or complete fracture-closing is the main reason of permeability drop, and furthermore, both softening and creep are the major factors of self-closure of mudstone fractures, and especially, the softening behavior plays an absolutely fundamental role. The numerical analyses show that either a higher in-situ stress or lower fracture density can obviously become one of the advantageous conditions for fractured mudstone layers to restore towards impermeability. These results are also verified by the engineering observation in Yili No. 4 mine of China. There obviously existed the recovery of water-blocking capacity of overlying strata after a period of time. We hereby recommend this investigation as refences for underground mining or engineering construction involving mudstone.
Rock Mechanics
K. Bour; K. Goshtasbi
Abstract
The design of underground spaces is mainly carried out using empirical, analytical, and numerical methods. The convergence confinement method (CCM) is an analytical technique that is widely utilized in analyzing the stability of underground spaces. However, the main challenge in the stability analysis ...
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The design of underground spaces is mainly carried out using empirical, analytical, and numerical methods. The convergence confinement method (CCM) is an analytical technique that is widely utilized in analyzing the stability of underground spaces. However, the main challenge in the stability analysis is the selection of an accurate constitutive model for rock mass, and particularly, its post-failure behavior. The existence of water plays a significant role in the stability analysis, whereas this effect is not usually considered in the CCM method. In this research work, a circular tunnel in a saturated medium is modelled and compared with its dry condition. Two types of constitutive models namely elastic perfectly plastic (EPP) and strain softening (SS) are used and compared in order to investigate the effect of water and post-failure behavior on the stability of tunnels. With this respect, the codes are written and incorporated in the constitutive models and various analyses are carried out. The results achieved from the analyses show that the elastic reaction of ground in the presence of water in both constitutive models are the same and that the ground reaction curves (GRCs) and longitudinal deformation profiles (LDPs) are similar. However, the trend of GRC is different in the case where the rock failure occurs and the face of the tunnel goes beyond 0.5D. According to the results obtained, the maximum displacement in a saturated medium with different K values for the SS model is more than that for the EPP model.
