Study On The Bearing Characteristics Of Continuous Box Structure In Mining Area

Bridges and culverts are important ways to connect the traffic. Box structure, as an important form of resistance to deformation, has been widely used in mining area. There are many researches on bearing capacity and resisting deformation of box structures, but less on the continuous construction of box structures, and most of them are water culverts. Taking 4# box structures under railway line at Zhangji North Mine as background, the multilayer continuous construction has been studied. Because of the higher total height of box structures after completion, being 10 meters, this paper has proposed to set buttress outside the side wall of box structures, refering to the design of counterfort retaining wall. This paper, taking two structure forms of no buttress box structures and buttress box structures, has mainly analyzed the box structure stress variation of ballast thickness, tilt height and closed or not after the completion of box structures through ANSYS software.The maxium stress value of the two structure forms increases gradually as heightening the thickness of ballast.The stress value reaching maximum of box structures is about 1.20~3.00 times of the stress value before mining, while the stress value of no buttress box structures is 3.0 times of the stress value of buttress box structures.There are tilt and curvature in addition to subsidence. Because of the smaller lateral dimension and the vertical deformation joint settlement, this paper only considers the tilt section uniformly sloping effect on box structures. With the increase of the slope, the stress of two structure forms increases first and then decreases. In general, the stress value reaches maxium while the slope being 30‰ or 40‰.The stress value of box structure with buttresses is 2.30~3.00 times of the box structure’s value without buttresses. Therefore, the buttress box structure plays an important role in protecting the sidewall, and the buttress box structure is a reasonable structure form for continuous construction of box structures. In the heightening process, the stress of buttress box structures can also be influnced by the factors of height and closed or not after the completion of box structures. It will be heightened 3 times under the influence of mining. Anslysing each model after heightening, the law of stress evolutionin can be obtained: the tensile stress and the stress in X direction reaches the maximum after the first heightening, and the pressure stress of sidewall reduces with the heightening process; the tress of box structure baseplate reaches minimum after the first heightening, then increases gradually with the heightening process. After analysing the box structure model being closed or not, it can be concluded that box structure with slab structure is more advantageous to the structure.Finally, analyzing the optimization design of reinforcing bar connection method and the sequence of backfill inside and outside the box structure, we can draw a conclusion that reinforced straight thread connection is an ideal method and the corresponding implementation plan is given. After the continuous construction, the soil inside the box structure should be backfilled first in order to assure the safety of box structure.