Abstract:

The service life of Metro tunnel constructed by mining method would be affected by cracks and corrosion of and hollows behind support structure. In order to improve the detection and recognition accuracy of support structure disease of Metro tunnel constructed by mining method, models of common shaped hollows, hollows contained with water, support structure gaps filled with different dielectrics and hollows behind steel grating arch and Hshaped steel arch are established by finitedifference timedomain method(FDTD). The propagation rules of ground penetrating radar wave in tunnel support structure are analyzed; the reflected results of different support structure diseases are analyzed; and a case study is made on engineering detection of Line No. 3 of Qingdao Metro. The results show that: 1) The radar reflection waves of hollows usually show as hyperbolic curves and their signals are strong. The radar images of triangle hollows which show as parallel inclined lineup are greatly different from those of other shaped hollows. 2) When the hollows and support structure gaps contained with water, the radar reflection waves are clearly visible at bottom of hollows and support structure gaps. 3) The steel structures of support structure have great influence on the detection and recognition of tunnel structure diseases; as a result, the diseases detection of primary support and secondary lining should be carried out respectively.

Key words: tunnel constructed by mining method, tunnel support structure disease, ground penetrating radar, finitedifference timedomain method, forward modeling