Abstract:

A shield tunnel is being constructed closely crossing underneath the FuxingmenXidan largecrosssection tunnel of Beijing Metro Line 1 with unreinforced secondary lining. As such, to ensure the stability of structures and facilities, controllable deformations, and normal operation of trains during the construction of the shield tunnel, the overall condition of the undercross section is assessed as Grade 3 (serious disease) based on the current situation. Moreover, key construction technologies related to shield tunneling through largecrosssection tunnels with plain concrete secondary linings are proposed herein. These technologies involve structuraldamage control with respect to the Line 1, aramid fiberbased adhesion, steel platebelt reinforcement, grouting reinforcement outside the tunnel of Line 1, shield tunnelingparameter control, and monitoring and measurement. The following conclusions can be drawn from the obtained results. (1) The strength, stiffness, and stability of the unreinforced structure after reinforcement using aramid fibers and steel plate meet the requirements, and no structural cracking or block dropping occurs. (2) Undertaking grouting on both sides of the section of the shield tunnel near the crossing on the existing line through the guide tunnel can effectively reduce the drilling hole length and improve drilling and grouting accuracies. In addition, the guide tunnel provides effective support for Line 1. Furthermore, the jack supporting measure is set in the lower passing section of the guide tunnel to improve the settlementcontrol effect. (3) The setting of the test section, optimization of the tunneling parameters, filling of the clay shock, and synchronous and secondary grouting have substantially positive settlementcontrol effects, thus reducing the impact of the construction work on the existing line and operation of trains and ensuring safety and satisfactory quality with respect to the construction.

Key words:

earthpressure balance shield, largecrosssection tunnel with unreinforced secondary lining, structural damage