Failure Mechanism and Deformation Characteristics of Gob-Side Entry Retaining in Solid Backfill Mining: A Case Study

In solid backfilling mining, gangue and other solid materials are backfilled into the gob to restrain the roof subsidence. As a result, instead of being subjected to periodic collapse, the overlying strata will be able to maintain its integrity and bend or sink as a whole with partial fracture and failure, thus facilitating the gob-side entry to retain. To study the mechanical deformation characteristics and failure mechanism of such gob-side supporting wall, this research analyzes the structure features of the surrounding rock in gob-side entry and builds mechanical damage model for gob-side supporting based on the hypothesis of planar slip surface in the theory of Coulomb earth pressure. The relationship among normal force acting on the contact face N, the angle between the slip surface of gangue and vertical face eta and other relevant factors are discussed. The result suggests that eta is mainly affected by delta, the friction angle between the backfill body and the supporting wall interface, and phi, the internal friction angle of backfill materials; eta increases as delta increases and decreases as phi increases. N, mainly affected by delta, phi and uniformly distributed load q, has positive correlation with q and negative correlation with delta and phi. The research also reveals that compressive stress exists only when the width of wall exceeds 1.741 m; such stress will decrease sharply when the width of wall is between 2 m and 3 m, and become stable when the width goes beyond 3 m. According to numerical simulation and field test, the maximum values of roof-to-floor longitudinal deformation and lateral deformation between two sidewalls are 350 mm and 210 mm, respectively. The research results proved that the model employed can accurately predict and evaluate the deformation and damage of the gob-side entry.