International Journal of Geomechanics

One-dimensional viscous behavior of clay was evaluated by performing drained one-dimensional compression tests, and drained triaxial compression tests. In both types of tests, the strain rate was changed stepwise many times and creep tests were performed several times during otherwise monotonic primary loading, unloading, and reloading. The specimens were: (1) saturated specimens of undisturbed clays; (2) normally consolidated saturated clay specimens reconstituted by consolidating slurry of clay chips from undisturbed samples and clay powder; and (3) specimens prepared by compacting wet, air-dried, and oven-dried powder of several different clay types. One-dimensional viscous behavior, which can be described with $\beta$ value of clay, is significant in all types of clay specimens. The observed viscous behavior of clay specimens is successfully simulated by a nonlinear three-component rheology model of the isotach type.

Evaluating the stresses in backfilled stopes constitutes a critical step for insuring underground mine safety and for analyzing backfill response. In recent years, the writers have presented several methods for conducting numerical and analytical investigations to assess the stress state in backfilled stopes. The results have shown significant stress transfer to the rock mass along stope walls which induces an arching effect. To date, most solutions have been developed for (sub-) vertical openings. In this paper, the results of an extensive numerical investigation on inclined stopes are presented. Emphasis is placed on the influence of stope geometry, backfill properties, and filling sequence on the stress distribution in the backfill. Results indicate that for a given stope geometry, the most influential factors are the backfill shear strength parameters (cohesion $c^{\prime }$ and friction angle ${\varphi }^{\prime }$ ), Poisson’s ratio $\mu$ , and dilatation angle ${\psi }^{\prime }$ . Some of these parameters not only affect the stress magnitude, but also the distribution pattern which is shown to also depend on the filling sequence. One of the main outcomes from this study indicates that increasing the value of $c^{\prime }$ tends to change the mechanical response of backfill from that of a particulate material to that of a consolidated medium, with each layer responding somewhat like a bending beam under vertical loads. The numerical results are compared to others obtained in previous investigations and also to analytical solutions and experimental test results obtained on a physical model. These are discussed in relation to the effect of the influence factors and their implications for the analysis of backfilled stopes.

Soil loss during tunneling may induce the ground deformation. The loss volume depends on tunneling methods, soil types, workmanship, etc. The movement pattern along the tunnel section can be separated into two parts: one part of which focuses on the planed center of the tunnel, and the other translates in the vertical direction. On the basis of the complex variable theory for elasticity, the corresponding second part movement could be deduced if the first part is predetermined. This paper studies the ground deformations under four possible focusing movement patterns. A comparison between the solutions and measured data is conducted for five different tunnels. It is proposed that the third focusing movement pattern could be presumed for predicting tunneling-induced ground deformation.

This paper presents finite-element analyses of excavations by using a coupled deformation and flow formulation. Specific numerical procedures were implemented into the finite-element codes to simulate the excavation construction and to solve the nonlinear coupled system. The paper discusses results of two generic excavations, with analyses conducted using different constitutive models and different excavation rates. Although the constitutive model affected the magnitude and distribution of the excess of the pore-water pressure due to the excavation process, the constitutive models only slightly influenced the dissipation rate of the excess pore-water pressure. Excavation rates that were one order of magnitude smaller than the hydraulic conductivity of the soil led to results representative of drained processes. Because of the slow rate needed for drained conditions, partially drained conditions normally prevail during excavations, highlighting the importance of coupled analyses.