Research and application on the “multi-layer” filling body with foamed expansion filling material for gob-side entry retaining gateway

Gob-side filling body consolidated by inorganic filling materials had gradually been widely used in gob-side entry retaining technology and engineering. However, the excessive stiffness of traditional filling body leads to severe damage of filling body and surrounding rocks under overburden pressure, especially in large mining height mining faces. To solve the problem of stiffness failure of filling body, a new filling material added with foaming agent and fibers was developed. Besides, a "multi-layer" filling body composed of conventional filling material(CFM) and foamed expansion filling material(FFM) was designed and applied. The failure characteristics and mechanical behaviors of the "multi-layer" filling body were studied by numerical simulation and field monitoring. The results demonstrate that FFM sample showed a weakened brittleness and enhanced compressibility to presented a tensile and shear failure mode under uniaxial compression. The "multi-layer" filling body composed by the upper part with a height of 0.5 m FFM layer and the lower part with a height of 2.5 m CFM layer was designed to adapt to roof sinking by "deformation-yielding". The upper part of "multi-layer" filling body formed by FFM had high compressible deformation property to absorb and transfer roof pressure to the coal side and reduce the vertical stress of roadway roof. The stress concentration of filling body and its own bearing environment were optimized. The damaged area of the "multi-layer" filling body composed mainly concentrated inside the upper part and the surface of the lower part in the filling body. The bearing area inside the "multi-layer" filling body was approximately rectangular. Through the application of the "multi-layer" filling body for gob-side entry retaining gateway, the stability of filling body had been improved significantly. The average shrinkage rate of roadway cross-section was 20%～30%, which was able to satisfy the requirement of the subsequently mining.