Effects of twin tunnel undercrossing excavation on the operational high speed railway tunnel with ballastless track

Abstract

The high speed railway tunnel, with the train running at a speed of 350 km/h (designed speed up to 350 km/h), is pretty sensitive to the disturbance caused by new undercrossing tunnel excavation. Hence, control requirements on the existing tunnel structure are particularly rigorous. The allowable geometric deformation in regular maintenance and the installation accuracy error of the ballastless track of high speed railway are considered. This paper puts forward the control requirements on displacement and structural stress of existing tunnel and the track irregularity induced by the construction of undercrossing earth pressure balance (EPB) twin-tunnels. Then, based on refined numerical analysis, the effects of the undercrossing twin-tunnel excavation on the existing Liuyang river high speed railway tunnel, in Changsha, China, were investigated considering the tunnel lining construction joints. Compared with previously centrifuge model test results and field measurements, the numerical results show that the presence of the existing tunnel reduces ground settlement induced by the undercrossing tunnel excavation, but such shielding effects will be weakened if considering the construction joints in the existing tunnel. However, the numerical analysis results, without considering the construction joint, underestimates surface ground deformation and overestimates the stress performance of the existing tunnel structure. The relative position between the shield tunnel center line and the existing tunnel construction joint determine the undercrossing position of the twin-tunnel, which has a great influence on the stress and deformation of the existing tunnel. It is suggested the middle line between new twin-tunnel is located directly below the construction joint of the existing tunnel to ensure a symmetric undercrossing excavation, especially in the ground deformation sensitive area.