Effect of a fault and weak plane on the stability of a tunnel in rock—a scaled model test and numerical analysis

Abstract

Scaled model tests were performed to investigate the effects of (1) faults, (2) weak planes, and (3) grouting on the stability of a tunnel. Numerical analyses were carried out and the results compared with those of the scaled model tests. When every parameter is properly scaled down in accordance with the scaled-down geometry, it is possible to represent the geological conditions of the operation site with the scaled model.Four different types of model were made to investigate the effect of a fault on the stability of a tunnel, and five different model types to examine the influence of weak planes and grouting effects. A mixture of sand, plaster and water was used to reproduce the scaled-down physical properties of rock and weak planes. The scale factor of the model was checked with field conditions. A hydraulic biaxial compression testing machine was used. Numerical analysis using FLAC 2D for the actual scaled model test was carried out as shown in Fig. 1. It was observed that the amount of deformation and the size of the plastic region increased as the distance from a fault to the tunnel decreased. When a fault was located across the upper part of the tunnel, the displacement of the crown was greater than when the fault was located to the left of the tunnel.The numerical analysis also showed that the tunnel was found to be stable when the cellular arch method (CAM) reinforcement was installed around the crown of the tunnel. However, better stability was obtained when the region above the crown of the tunnel was systematically grouted. 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 along the weak plane. Numerical analysis presented quantitative values comparable to the results of the scaled model tests. ARTICLE IN PRESSFig. 1. The failure zone and plastic region around the tunnel in the scaled model test, (a) pressure=3.0 kg/cm 2 , (b) plastic region by FLAC 2D analysis.

Numerical simulations of failure behavior around a circular opening in a non-persistently jointed rock mass under biaxial compression

“…Such discontinuities can aggravate stress concentration and strength degradation, thus resulting in different patterns of rock mass failure around the opening compared with the patterns observed in isotropic rock masses. According to the number of discontinuities considered, related analytical models can be classified into three main categories, namely: a 'one-joint' model [10][11][12][13]; a 'single set of joints' model [8,[14][15][16][17][18]; and a 'multiple set of joints' model [19][20][21][22]. The 'one-joint' model is particularly used to investigate the effect of a fault, which is a large geological discontinuity, on the deformation and failure behavior of an underground opening.…”

Rock failure with weak planes by self-locking concept

“…(8,9) and (1,2) are different in appearance, transformation can be made to prove the equivalence, which indicates that the model based on self-locking concept gives the same results as that of Mohr-Coulomb criterion for weak planes.…”

“…In geotechnical engineering, the influence of mechanical parameters of weak planes are included, such as in numerical procedures in the analysis of tunnel stability [9][10][11], or for surface deformation [12] caused by production of coal formation with weak planes. In drilling wells in the petroleum industry, wellbore stability can also be affected by weak planes [13,14].…”

“…(1,2) are expressed by t and s in local coordinate system, and Eqs. (8,9) are represented by s 1 and s 3 in global coordinate system, which are essentially the same.…”

Experimental study on similarity materials for soft rock of deep-buried tunnels

“…Every external condition containing force condition may cause multiplicity of material properties. Therefore, before the start of the model test, all of the simulation objects should be analyzed specially, so as to find the appropriate similarity materials to make the model (Hanif and Darwish, 1993;Liu et al, 2003a;Jeon et al, 2004).…”