Ground surface settlements due to construction of closely-spaced twin tunnels with different geometric arrangements

• Closely-spaced twin tunnels with various geometric arrangements are presented.
• A method is adopted to describe the settlements due to the twin tunnels construction.
• Surface settlement data induced by each of the twin tunnels are presented.

This paper examines the ground surface settlement profiles due to the construction of closely-spaced twin tunnels using the shallow tunnelling method. In the concerned zone, where the twin-tunnelling was performed in stacked and offset arrangements, the ground surface settlements of in total 18 cross-sections were continually recorded during construction. To cater for different conditions of the twin tunnels in the concerned zone, partial face, full face and forepoling reinforcement schemes were adopted. The recorded surface settlements and settlement troughs of three typical sections are reported and illustrated. The surface settlement troughs induced by each of the twin tunnels are fitted by the Gaussian function. The parameters that characterize the surface settlement troughs induced by each of the twin tunnels, such as the maximum settlement, percentage of ground loss, trough width and empirical trough width parameter are presented and compared.