The Deformation Reserved (DR) method is a commonly used stress release method in the construction of weak rock tunnel with high geostress. The excavated tunnel section is usually larger than its design size, a space is reserved outside the design excavation boundary of the tunnel. The behavior of the double-layer support structure was investigated through theoretical derivation, and the applicability of the DR method in controlling the large deformation of soft surrounding rock during tunnel construction in high geostress was discussed. The calculated results by proposed method were verified by the in-situ monitoring data of field test. It is found that the DR method is capable of releasing the high geostress when tunnelling in squeezing rocks, and the double-layer support structure is necessary to resist the high ground stress.
Tunnel engineering has advanced towards larger sections and greater burial depths, particularly in central and western regions (Xu et al., 2021a). Many tunnels traverse areas of soft, broken rock with high in-situ stress, where they are impacted by the substantial deformation caused by the high ground stress of the soft rock (Kang et al., 2022, Guo et al., 2022, Wang, 2022). Soft rock tunnels under high ground stress undergo significant deformation, which can persist for extended periods and seriously impact construction progress and safety (Xu & Xia, 2021, Xu et al., 2021b, Ding et al. 2017). In response to the challenge of constructing tunnels in high ground stress soft rock with large deformation, both domestic and foreign scholars have undertaken corresponding studies. As early as 1998, Ortlepp and Stacey (1998) suggested that the use of higher strength support structures to resist large deformations in soft surrounding rocks is impractical and requires higher costs. Cantieni and Anagnostou (2009) pointed out that using yielding support to allow for displacement of surrounding rock is an effective way to deal with large deformations during tunnel excavation. Stress in the surrounding rock is partially released as it is displaced. Typically, this stress release is achieved by installing a yielding support system and allowing a certain amount of over-excavation and reserved deformation (Cui et al. 2021).
