Traditional Limit Equilibrium Method Research Articles

Characterization of phyllites for tunnelling

In traditional tunneling, an analysis of the face stability is required to avoid failure mechanisms or excessive face extrusion. Face reinforcement can improve face stability and reduce deformations. In the present work a numerical study of both unreinforced and reinforced tunnel excavation faces by means of 3D FEM analyses is presented. The results are compared with those of the traditional limit equilibrium method and with an analytical solution based on previous numerical studies. It could be shown that the LEM may lead to non-conservative results. Finally, the deformation response is assessed and the benefits of face reinforcements are investigated.

Numerical modelling of progressive damage and associated fluid flow using a hydro-mechanical local degradation approach

In traditional tunneling, an analysis of the face stability is required to avoid failure mechanisms or excessive face extrusion. Face reinforcement can improve face stability and reduce deformations. In the present work a numerical study of both unreinforced and reinforced tunnel excavation faces by means of 3D FEM analyses is presented. The results are compared with those of the traditional limit equilibrium method and with an analytical solution based on previous numerical studies. It could be shown that the LEM may lead to non-conservative results. Finally, the deformation response is assessed and the benefits of face reinforcements are investigated.

Numerical study of parameters influencing the response of flexible retaining walls

A practical numerical model is described for analysis of flexible retaining walls. In terms of capabilities, the model fits between traditional limit equilibrium methods and full finite element approaches; it overcomes many of the limitations associated with the former but is not equipped with the versatility offered by the latter. Using an approach similar to that adopted in boundary-element based models, the wall stiffness is represented by a series of elastic beam elements whose stiffness is combined with that of the prestressed struts and the soil to form, the overall stiffness matrix. The stiffness matrix of the soil is obtained by inversion of flexibility matrices generated by interpolation and sealing of flexibility matrices calculated for a simplified soil model using finite element methods. The soil behaves linearly elastically, as long as the pressures correspond to stress levels lying between the limits. Where the lateral displacement of the wall corresponds to a pressure outside of these allowable limits, correction forces are added until the resulting pressures are within the active or passive pressures. Arching is permitted by considering the forces acting on the wall compared with the forces consistent with possible failure surfaces within the soil. Other features that can be accomodated by the model include struts, variations in water table, and the effects of surcharges. The proposed model has been shown to capture the displacement, anchor loads, and lateral stresses for several field problems. Based on these studies and other field applications of the model a number of points have been observed that are of practical interest; these points are separately listed. Key words: numerical analysis, retaining wall, anchor, arching, soil–structure interaction, deflection.

Generalized Slope Stability Analysis: Interpretation, Modification, and Comparison

The results of a generalized variational slope stability analysis, which is rigorous in the framework of limit equilibrium, are presented. To alleviate possible intimidation due to the abstract nature of the variational analysis, interpretation is provided showing this analysis to be equivalent, in principle, to traditional rigorous limit equilibrium methods. The variational approach, however, is more efficient in the sense that no guessing of a force-related function is needed to obtain a statically determinate problem, nor is it necessary to assess the results for static reasonableness. Consequently, its application is simpler than other rigorous methods. A simple yet efficient numerical scheme, requiring the solution of only three simultaneous nonlinear equations, is illustrated. All the algorithms necessary to assemble a computer program are explicitly given. Several complex problems are analyzed, comparing the results with the predictions of the Morgenstern-Price and Janbu methods. This comparative study indicates the applicability of the variational analysis, suggesting it is on par with other rigorous methods.

Analysis of a rock slope with internal dilation

A class of rock slope failures exists in which the mode of failure requires the existence or creation of internal shears to accommodate large internal slide mass distortion. These internal displacements are required to allow motion along the basal slip surface. This paper demonstrates that the more traditional limit equilibrium methods of analysis are often conservative when used to assess the stability of slopes with this failure mechanism. As a result, back analysis may overestimate the available shear resistance. A method of analysis capable of handling this failure mechanism was proposed by S. K. Sarma. A case history from the Revelstoke Hydroelectric Project, British Columbia, is used to demonstrate that these internal shears were required for movement to occur and that passive anchors inside the sliding rock mass can be used to improve the overall slope stability. No attempt is made to evaluate the actual factor of safety of the three-dimensional slide mass. Key words: rock slope, foliation shear, stability analysis, dilation, internal shears, passive anchors.