Investigation of fill distribution in post-injected longwall overburden with implications for grout take estimation

In civil and mining engineering, grout injection technology, which involves the injection of grout into the bedding separation zone or other voids through surface boreholes, is used to stabilize the ground above underground excavations. The injected fill at the targeted void space mitigates the deformation of overlying strata, thus reducing surface subsidence. When applying this technology it is important to determine the distribution of the injected fill in the overburden, as it affects grout take estimation, evaluation of subsidence control effectiveness, etc. In this paper, we present theoretical and physical models of the distribution of the injected fill. According to previous borehole data, the location of the injected fill is assumed to be a single horizon. Based on the characteristic of the main injection horizon and geological features of the surrounding strata, an easy-to-use theoretical model of injected fill distribution is proposed, which quantifies the fill thickness at different locations along the main injection horizon. The proposed model is verified using a physical model of overburden grout injection. In addition to the injection parameters such as the horizon depth and ratio of injection, a site-specific geological parameter, namely the angle of full subsidence, as well as the underground opening width, play a vital role in governing the fill distribution. Using the proposed model, we develop a method for estimation of grout take, which may facilitate the injection design, thus improving the effectiveness of ground stabilization. (C) 2016 Elsevier B.V. All rights reserved.