Abstract：
During the construction of a small-space twin-tube tunnel underneath a mined-out area, the distur? bance from an adjacent tunnel excavation will be superimposed and the stability of the mined-out area is seriously affected. An indoor similar model test of a small-space twin-tube tunnel underneath the mined-out area was carried out and the settlement of the rock mass and around the mined-out area during excavation was monitored. Considering the two cases of formation dip angles of 15 ° and 25° in the mined-out area, the simulation of formation discreteness in the mined-out area and the similarity of the model to prototype was achieved by controlling the rock compressive strength and porosity in the mined-out area. Test results show that: 1) there are three extreme ground settlement points located in the left tunnel, right tunnel and middle rock wall of the mined-out area, respectively, with the maximum ground settlement occuring above the pilot tunnel; 2) the greater the dip angle is, the larger the settlement is and the wider the range of settlement is; 3) the maximum settlement induced by the small-space twintube tunnel excavation is about 35% to 74% higher than that of single-tube tunnel excavation, and the impact of pilot tunnel excavation on the settlement above the subsequent tunnel is less than that of the following tunnel excavation on the settlement above the pilot tunnel in the mined-out area; and 4) the settlement process of the mined-out area can be divided into six stages, and the settlement develops quickly during excavation of the left and right tunnel underneath the mined-out area. In order to avoid the extension of the disturbance range during the following tunnel excavation, excavation of the following tunnel should be performed after stabilization of the mined-out area settlement induced by the pilot tunnel excavation or installation of the secondary lining of the pilot tunnel.
2016, Vol. 53 