Model tests on loading characteristics of linings in overlying horizontal coal mined-out area

The tunnel construction adjacent to the overlying mined-out area is easy to expand the rapping range of the overlying rock and to increase the loose load. In order to study the characteristics of lining structures under loads in overlying horizontal thin coal mined-out area, indoor scaled model tests are carried out to measure contact force between tunnel lining and surrounding rock and structural internal force of the secondary lining (axial force and bending moment) in the strata thin seam mined-out area. The variations of displacement, axial force and bending moment under different pressures and the influences of pitch under confining pressure on the earth pressure and internal forces of the secondary lining are analyzed. The results show that the overlying mined-out area has a certain effect on convergence displacement of tunnel. The smaller the distance, the greater the displacement and the more obvious the increase of bending moment and axial force. The internal force of the secondary lining is discretely distributed, the maximum eccentricity distance appears in the invert site and the bearing capacity has a certain degree of reduction, so it is the weak part of the main structure of the tunnel. The first crack appears in the inverted arch of the secondary lining, and the overlying mined-out area has remarkable influence on the order of cracks.