Settlement and Load Transfer Mechanism of Pipeline Due to Twin Stacked Tunneling with Different Construction Sequences

Abstract

The tunnel-pipeline-soil interaction is attracting more and more wide range of scholars and was treated as a plane strain problem, with little attention given to the responses of existing pipeline to twin-tunneling process with different construction sequences. Moreover, there are rare reports available on the influences of tunnel construction sequences on an existing pipeline. In this study, a three-dimensional centrifuge model test and numerical simulations using an advanced hypoplasticity constitutive model were conducted to investigate the influences of twin stacked tunneling with different construction sequences on an existing pipeline. The results shows that the maximum values of greenfield ground settlement, pipeline settlement and additional pipeline bending strain due to twin stacked tunneling when the upper tunnel was excavated first were 25%, 18% and 11% larger, respectively, than those when the lower tunnel was excavated first. The maximum values of greenfield ground settlement, pipeline settlement and additional pipeline bending strain due to twin stacked tunneling when the lower tunnel was excavated first were slightly smaller than those when the twin tunnels were excavated simultaneously. After the twin-tunneling process, the sagging regions were located within ± 1.5DT (tunnel diameter) in these three conditions. The maximum pipeline bending strain within the hogging regions was approximately half of that within the sagging regions. Because of shielding effects from the upper tunnel, the region where vertical stress of the soil reduced was transferred to both sides of the tunnel due to the second tunneling process when the upper tunnel was excavated first. As a result, the extended sagging regions due to the second tunneling process when the upper tunnel was excavated first were two times than that when the lower tunnel was excavated first.