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

TLDR

Tunnels in loose deposits are prone to collapse and excessive lining deformation, making excavation scheme selection critical for safety and operation. The study used the Tingziba highway tunnel in loose deposits, performed CD compression tests on reconstituted specimens to determine mechanical parameters, and then 3‑D modeled stress and deformation for three excavation schemes. Analysis revealed that single‑side heading tunneling reduced vault displacement and plastic zone development, outperforming other schemes, and the findings are relevant for tunnel design in similar loose deposit settings.

Abstract

Because 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 single-side heading tunneling was more suitable for this tunnel and could both reduce vault displacement and constrain plastic zone development. The results should be significant for tunnel design and construction in similar geologic environments.