Abstract:

In this paper, an attempt is made to optimize the location and design procedure of the backfill stopes according to the some geotechnical parameters. In this regard, a large number of numerical models were made using FLAC 2D software, because of the plane strain condition. So shallow, semi-deep and deep individual stopes has been defined. Since all stopes in this paper are considered as individual excavation, there is not any conventional pillar, although arching effect on this post pillar areas have been investigated as one of the main objectives. In order to determine the stress state in the backfill and its surrounding area, volumetric strain energy released within the fillings has been used as an indicator. This parameter can explain the backfill state (active or passive form) and indicates the efficiency of the backfill. Finally, volumetric strain energy released and stress state within the backfill has been plotted versus variable geotechnical parameters. So this paper presents a design procedure and locating approach of the backfill stope according to the geomechanical issues.

Introduction

Backfilling has become a standard practice in mining operations. One of the main reasons behind the extensive use of backfill in mines is that it can lead to a significant reduction of the amount of wastes disposed on the surface. Backfilling thus protects the landscape and reduces the potential for environmental impacts such as acid mining drainage (when sulphide minerals are present). Despite this advantage, it must be kept in mind that the main role of mine backfill is to provide ground support to ensure stope stability and improve ore recovery by reducing dilution [1]. It is thus important for ground control engineers to have well adapted tools that allow a relatively fast and reliable estimate of the stress state in and around backfilled stopes. In this regard, it must be recalled that most backfill materials, even those that include a significant portion of binder, are relatively soft and show a low yielding strength compared to the surrounding rock mass [2]. As a consequence, the backfill placed in a stope tends to settle significantly, often producing fairly large strains (of 5% or more) [3]. The deformation of the backfill may then induce some load transfer along the interfaces due to the frictional forces that develop along the contact with the rock mass [4]. This type of phenomenon, often encountered with confined backfills, is known as arching [5].

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