Physical and numerical model simulations have been performed to determine the surface subsidence induced by underground opening under super-critical conditions. The study is focus on the effects of opening geometry and block size of the overburden on the angle of draw (λ) and the maximum subsidence (Smax). Granular materials are used to simulate individual blocks in overburden. The results indicate that λ and Smax decrease with increasing the block size-to-width ratio (Bs/W) ratios. The λ increases with opening height (H/W) and length (L/W). The Smax/W ratios and λ approach constant when the opening length-to-width ratios (L/W) is beyond 3. Under the same opening geometry, increasing the opening depth results in a reduction of λ and Smax. The results of discrete element analyses agree reasonably well with those obtained from the physical models. These verified numerical models can be extrapolated to predict the super-critical subsidence behavior of fractured rock mass.

1 Introduction

The behavior of the subsidence above the underground mining can impact the environment and surface structures within the mine area (Asadi et al. 2005). In order to minimize the environmental impact, a reliable subsidence prediction is essential. Some recent research results on subsidence behavior are summarized below.

Using FLAC3D, Dai et al. (2011) find that the surface subsidence extends widely and the surface deformations decrease with the increase of the layer thickness. Guo et al. (2011) demonstrated by using numerical models that the subsidence of strip pillar mining increases with the increase of mining depth. Li & Wang (2011) used PFC to simulate the process of subsidence and to calculate the distribution of contact force and displacement of ore particles, which have a good consistency in comparison with the actual survey data in Shandong province. Discrete element modeling is employed for this study due to its advantages in analyzing large deformations and discontinuous processes. Thongprapha et al. (2015) used physical model simulations to determine the effects of underground opening configurations on surface subsidence under super-critical conditions. They conclude the angle of draw the maximum subsidence and the volume of trough are controlled by the width, length, height and depth of the underground openings.

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