Analysis of inclined length effect of roof fracture and overlying strata catastrophe in steeply inclined longwall face: A case study

Abstract

In order to determine the optimal inclined length of steeply inclined working face, the fracture field, strain field, displacement field and strata movement trend of steeply inclined working face were monitored through physical simulation test and digital speckle technique. At the same time, combined with theoretical analysis, the movement law of overlying strata and the catastrophe mechanism of working face caused by the length effect of working face are deeply studied. The research results show that with the increase of working face length, the length and growth rate of middle extremely unstable region are always largest, followed by lower and upper. The spreading failure characteristics of “roof-overlying strata-roof” appear along the inclined direction. When the working face length is less than 125 m, the larger vertical displacement and horizontal displacement are concentrated in the middle extremely unstable region. When the working face length is greater than 140 m, the larger vertical displacement is transferred to the lower stable region and the larger horizontal displacement is transferred to the upper unstable region. Based on this, it is obtained that the working face boundary length of roof and overlying strata catastrophe is 125 m and 140 m respectively. Furthermore, it is put forward that the optimal working face length is 95 m ∼ 125 m on the premise of effectively controlling the hanging space instability in the upper goaf and the flying gangue disaster in the working face. The application of digital speckle technique in large deformation measurement of large-scale physical models is realized.