Abstract: This article presents a method for security discrimination of adjacent underground pipelines during the construction of twin shield tunnel. Based on Winkler elastic foundation beam model, a relationship is established between strain of continuous pipelines and surface settlement by considering pipe-soil interaction. Assuming that displacement of pipelines and displacement of soil are the same, an expression of relationship between joint angle of discontinuous pipelines and surface settlement is derived. Considering aging of pipelines, a reduction factor related to time is defined, and a method to judge the security of pipelines by measuring surface settlement is built. When the strain or joint angle of pipeline reaches the maximum safety allowable value, the corresponding surface settlement is the controlling value. The pipelines are in danger when the value of surface settlement exceeds the controlling value during the construction stage. Surface settlement monitoring data are used in this method to assess the state of subsurface pipelines and the state is not easy to be monitored. The reliability of this method has been indicated in the comparison between predicted value and measured value, and the horizontal spacing L value of twin tunnel has a great influence on the control value of surface settlement. When L is relatively small, the maximum value appears on the axis of two tunnels; when L is relatively large, the maximum value appears on the vicinity of the tunnel axis. With the increase of L, the maximum control value is gradually reduced.

Key words: twin shield tunnels, underground pipelines, security discrimination, surface settlement