Experimental investigation of undercut stratified rocks using base friction technique

چکیده مقاله

Excavation inside stratified rocks can be for mining purposes or construction of civil underground spaces. In coal mines, coal layers are usually placed between other layers of sedimentary rocks. One of the most important factors affecting the stability of the tunnel as well as the shape of the collapsed area above the tunnel is the angle of the layers. In this research, the influence of the bedding slope angle on the instability and failure mechanism in undercut inclined stratified rocks was investigated experimentally. One of the main challenges in physical modelling, especially for the rock engineering problems, is to reproduce the real filed conditions in the laboratory. In order to achieve the prospect behaviour of rock masses and for the demonstration purposes, simplifications may be applied. For this purpose, a total number of 20 physical model tests were conducted and the undercut process and the instability of the roof layers was modelled using a basic friction table, while a base friction powder was used as a modelling material. The results of this research show that in the case of horizontal stratified rocks, the length of the failed roof beams decreases from the bottom to the top, while in the case of inclined layers, the length of the beams increases from the bottom to the top, so that the longest beam is placed in the highest part of the unstable area. Also, increasing the span of the tunnel does not affect the shape of the collapsed area and only the area of the collapsed area increases and the amount of this increase is linearly related to span of the tunnel. Also, the 30 degree angle has the lowest and the horizontal mode has the most collapsed area at the top of the tunnel.