THE SETTLEMENT LAW OF RAILWAY BALLAST BEDS TRAVERSED BY A SHIELD TUNNEL AND THE CONTROL OF SHIELD CONSTRUCTION PARAMETERS

To study the settlement law and the key points of construction parameters of shield tunnels for controlling the subsidence of ballast beds caused by traversing construction of shield tunnels, based on the Beijing power transmission project of the cable shield tunnel beneath the Beijing-Guangzhou railway, the time course change and development trend of the settlement trough during the shield construction was analyzed using finite element numerical simulation and monitoring. A thorough investigation of the law of railway settlement and the control of shield construction parameters is conducted by analyzing shield construction parameters. The results indicates:1) The numerical model results of the subsidence of ballast bed and monitoring data have good consistency, and the subsidence of ballast bed was moderate due to a strict control of the shield construction parameters during the traversing process while a high rate in the prophase and later period was present; 2) The subsidence of railway could be effectively controlled by controlling the construction parameters of the shield tunnel. During the construction, the average value of shield excavation was controlled to be approximately 18.8 m³, which is approximately 1.25 times of the theoretical value. The pressure of the soil chamber maintained steady growth from 0.050 MPa to 0.054 MPa. The torque value was well controlled at 1150 kN/m-1200 kN/m. The synchronous grouting and secondary grouting cooperated well with the change of the pressure of the soil chamber through timely increase or decrease.