Comparative Analysis of Excavation Schemes for a Tunnel Constructed through Loose Deposits

AbstractBecause of weak surrounding rock, tunnels constructed in loose deposits are prone to collapse, and secondary linings commonly suffer excessive deformation. Therefore, it is important to select an appropriate excavation scheme, which will affect both tunnel construction safety and subsequent tunnel operations. This paper takes the Tingziba tunnel, a highway tunnel shallowly buried in loose deposits of diluvial and proluvial origin, as an example. During construction, this tunnel experienced many instances of vault collapse and advanced support destruction. Isotropically consolidated drained (CD) compression tests were carried out on reconstituted specimens to obtain the mechanical parameters of the loose deposits. Three-dimensional modeling was performed to simulate stress and deformation distributions in the tunnel after excavation by three different schemes, i.e., up and down bench tunneling, three-bench tunneling, and single-side heading tunneling. The comparative analysis results showed that si...