Analysis Of Underground Excavations Research Articles

An automated a priori knowledge-based p-adaptive three-dimensional finite element mesh improvement method for stress analysis of underground excavations with prismatic cross-sections

ABSTRACT With increasing modelling capabilities in geomechanics incorporating non-linear material behaviour, an increasing complexity of models representing excavation of tunnels can be analysed. Often, analysis is using finite elements, where problems size can be a controlling factor due to limited computational resources. An approach to analysing these problems is to optimise the discretisation of the differential equations by concentrating elements where solution accuracy counts the most. This paper describes a priori p-refinement method for mesh improvement for stress analysis of prismatic tunnels. The improvement results in a mesh with higher-order elements near regions of interest and lower-order elements elsewhere. The focus is on the automated insertion of transitional elements at the interface of the two regions, based on the zone of disturbance in the geomaterial. The method was incorporated into a finite element code, and its performance was tested on practical problems, where the global stiffness matrix size was reduced by 70%, and the calculation times were significantly shortened. The average difference compared to complex models without mesh improvement was less than 3%. It is anticipated that the presented method enables analysis of problems that would otherwise be beyond the current computing capabilities leading to safer and economical designs.

NON-LINEAR FAULT BEHAVIOUR NEAR UNDERGROUND EXCAVATIONS — A BOUNDARY ELEMENT APPROACH

A boundary element model for stress/stability analysis of underground excavations in the vicinity of faults is presented. The boundary element formulation adopts the fictitious stress method for the simulation of excavation boundaries and the displacement discontinuity method for the representation of faults. The numerical model employs the Barton–Bandis non-linear joint model for the modelling of the fault behaviour and linear elastic behaviour for the rock. An incremental-iterative in situ stress relaxation algorithm is implemented for the non-linear analysis of the faults. Both deformation and peak strength models of Barton–Bandis are incorporated for modelling the mechanical behaviour of the fault. The non-linear deformation of fault considers the effects of coupling between shear and normal stresses and displacement, joint closure, joint separation, hardening followed by post-peak or residual behaviour. The peak strength model employs a mobilized non-linear shear strength envelope. The differences between linear and non-linear simulation of the fault models are discussed. A comparison of model predictions with the classical Mohr–Coulomb peak strength model with constant joint stiffness is presented. The numerical model is used for a case study of Canadian hard rock underground mine. The shear and normal displacements along the fault during four mining sequences with backfill simulation are presented and discussed.

Analysis of underground excavations and their support systems : Elias, G Ph D thesis, California Univ, Berkeley, 1976, 118P

Analysis of underground excavations and their support systems : Elias, G Ph D thesis, California Univ, Berkeley, 1976, 118P