Computer Aided Design for Safety Analysis of Excavation in Stratified Rock Tunnel

Stratified rock mass is widely existing in tunnel engineering. The most relevant feature of stratified rocks is the occurrence of very persistent bedding, which makes the rock-mass highly non-isotropic. A number of techniques for designing underground excavations in stratified media have been described in the literature, like theoretical method and laboratory test, which can only be applied in analyzing the problem with simple geometry and costs much expense. Recently, with rapid development of computer technique, numerical simulation methods have been widely applied in engineerin. Among all the numerical simulation methods, fast lagrangian explicit finite difference code of continua (FLAC3D) is widely used to solve practical problems, especially in field of elasto-plastic characteristic, large deformation analysis and construction procedure. So in the present paper, numerical simulation for the failure mode of stratified rock mass after tunnel excavation is done by FLAC3D, which can give further guidance to understand the anisotropic characteristic of stratified rock mass.

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The Deviation of Semi-Theoretical and Semi-Empirical Water Inflow Prediction Formula Based on Sphere Coordinate Conversion and a Grouting Excavation Evaluation Method

Applied Sciences ◽

10.3390/app112411956 ◽

2021 ◽

Vol 11 (24) ◽

pp. 11956

Author(s):

Yonghong Wang ◽

Jiabin Li ◽

Chuan Wang ◽

Qin He

Keyword(s):

Numerical Simulation ◽

Rock Mass ◽

Fractured Rock ◽

Water Inflow ◽

Theoretical Formula ◽

Simulation Methods ◽

Confined Aquifer ◽

Fractured Rock Mass ◽

Numerical Simulation Methods ◽

Weight Method

The water in the rock medium is exchanged with the confined aquifer through the fracture, which leads to the water inflow line in the confined aquifer is no longer horizontal. This paper assumes that the aquifuge is a kind of semi-isolation layer, while the first-order derivative of the total head slope line function within the influence of precipitation approaches the slope of the line connecting the top plate of the aquifuge with the spherical center. This hypothesis demonstrates the relationship between the bottom of the well water inflow and the complete well gushing water. Laplace’s equation for the spherical coordinate transformation is used to find the analytical solution of the water inflow for stable flow. The calculation results are in line with reality through actual engineering and numerical simulation methods. The current numerical simulation methods and theoretical methods mostly consider the aquifer in the ideal state, which is difficult to simulate the fractured rock mass. The theoretical formula proposed in this paper can more effectively reflect the actual seepage situation of fractured rock mass than other formulas. In addition, the combination of theoretical derivation, numerical simulation and field measurement can predict the water inflow more accurately than unilateral research. At the same time, for the question of whether the face excavation is grouted or not, this paper using the subjective and objective assignment weight method combined with analytic hierarchy process method and entropy-weight method to take the weight calculation and giving a slurry excavation judgment method based on the proposed formula. Theoretical support is given for the selection of permeability coefficients for each hole in the overrun exploration and this method is validated by different projects, which has some degree of reference value.

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