In this paper, the effects of dynamic loads on the geometry of the failure zone occurring around underground openings, excavated in deep and massive rock masses, have been investigated. Following an elasto-plastic stress analysis of a two-dimensional underground opening under static conditions, dynamic loads have been applied. In the static and dynamic analyses, FLAC2D computer program has been utilized. Maximum ground acceleration value is selected as an input parameter. An index determining the relative size of the yield zone around the opening has been used for comparison of instabilities.

In diesem Bericht wurden die Auswirkungen von dynamischen Lasten, auf die Geometrie der Bruchzone in der Umgebung von Untertagehohlraumen, die in tiefen und massiven Gebirge aufgefahren wurden, untersucht. Nach einer elasto-plastischen Spannungsanalyse eines zwei-dimensionalen Untertagehohlraumes unter statischen Beanspruchungen, wurden dynamische Lasten aufgebracht. Fuer die statischen und dynamischen Analysen wurde das FLAC2D Computer Programm verwendet. Die maximale Bodenbeschleunigung wurde als Eingabe Parameter gewahlt. Zum Vergleichen der Unstabilitaten wurde ein Index verwendet, der die relative Grösse der Bruchzone in der Umgebung des Hohlraumes bestimmt.

Dans ce papier, l'influence des chargements dynamique sur la geometrie de la zone en rupture observee autour des cavites profondes excavees dans des massifs rocheux ont ete etudiees. Des chargements dynamiques ont ete appliques, dans le cas d'une modelisation bi-dimensionnelle de l'excavation d'une cavite profonde, sur la base d'une analyse elastoplastiques des contraintes en conditions statiques. Le code de calcul FLAC2Da ete utilise pour les analyses statiques et dynamiques. La valeur maximale de l'acceleration du sol est choisie comme paramètre d'entree. Un indice determinant la taille relative de la zone sollicitee autour de la cavite a ete utilise pour comparer les differentes instabilites.

Introduction

Underground openings should meet the stability requirements conforming with their function during their service life. In regions with seismic activity, the stability performance of an underground opening under dynamic loads is as important as its performance under static conditions. In the design, therefore, additional effects occurring around the opening due to dynamic loads (e.g. earthquake) should also be considered. If occurrence of an overstressed zone around the underground openings is unavoidable, the geometry (size and shape) of the failure zone should be determined under both static and dynamic loads.

In this paper, the effects of the seismic loading parameters, in situ stress field, and opening geometry on the stability of deep underground openings have been investigated. Using a numerical stress analysis program, static and dynamic analyses have been carried out for two-dimensional underground openings excavated in a rock mass with an elasto-plastic behavior. Also, the significant results are presented and discussed.

Analyses

In this study, FLAC2Dfinite difference program1 has been used for elasto-plastic plane-strain analyses of underground openings subjected to static and dynamic loads.

Opening Shape and In situ Stress Field

The analyses have involved mainly two opening shapes, i.e. circular and arched roof with varying width-to-height ratio (W/H). For the arched-roof shape, a parametric equation developed by Gercek2 has been used to obtain a finite difference mesh conforming to the opening geometry.

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