In this paper, stabilities of various underground openings are compared. For this purpose, the relative size of the overstressed zone occurring around the opening and the factors affecting the geometry of this region have been considered. Using an analytical solution and an empirical failure criterion, it has been possible to demonstrate the effects of opening geometry and in situ stress field on the expected stability.


Dans cet article on a essaye de comparer la stabilite de diveres ouvertures souterraines en tenant compte de relative grandeur de la zone d'ultra tension autuor des ouvertures et les facteurs affectant la geomerie de cette zone. En utilisant une resolution analitique et un critere du rupture empirique on a reussit à demontrer les effects d'une part de la geometrie d'ouverture et d'autre, Ie champ d'etat de contrainte in situ, sur la stabilite.


In diesem Bericht, wurden die Standfestigkeiten verschiedener Untertagehohlraume Verglichen. Mit dieser Absicht, wurde die relative grösse in der Umgebung des Hohlraumes entstehenden Überspannungszone und die Faktoren die die Geometrie dieser Zone beeintlussen berucksichtigt. Mit der Benutzung einer analytischen Lösung und eines empirischen Bruchkriteriums, konnten die Wirkungen der Geometrie des Hohlraumes und des primaren Spannungsfeldes auf die Standfestigkeit gezeigt werden.


In the design of underground openings in massive elastic rock, determination of stress distribution, especially overstressed regions, around the opening is considered to be a key step. According to Hoek & Brown (1980), " …qualitative evidence from practical experience does tend to suggest that there is a reasonable correlation between the zone of overstressed rock predicted from elastic theory and the stability and support requirements of underground excavations. In fact, many underground excavation designers use the elastic theory predictions as rough guidelines in judging the excavation stability …" If the elastic stress analysis predicts some kind of failure, optimization of design variables is necessary to restrict the extent of boundary failure and the zone of failure around the excavation. For the design of single openings of two dimensional nature (e.g., tunnel, gallery, etc.), excavation geometry and orientation are two of the few design variables and the designer is expected to make practically feasible modifications involving these variables. In some instances, when the excavation geometry is not a design constraint, the designer is faced with the task to determine the optimum opening geometry for a given set of conditions (i.e., in situ stresses and rock mass quality). One of the ways to achieve this objective is to compare the expected stability by studying the overstressed regions around excavations having various geometries. In this paper, an approach is presented for the comparison of stabilities of various non-circular underground openings excavated in massive or jointed (three or more joint sets) rock masses. In the following sections, first, the methodology used in this approach is briefly explained. Then, the effects of opening geometry and in situ stress field on the expected stability are demonstrated by using a number of charts obtained by a series of parametric study.


The methodology employed for the prediction and comparison of overstressed regions around underground openings is shown in Fig. 1, and the fundamental aspects of this approach are summarized below.

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