Development of similar materials for typical coral reef limestone and stability analysis of tunnel excavation in soft-hard interbedded stratum

The development of underground space in island and reef environments is a key trend in marine engineering. This study aims to develop suitable similar materials for coral reef limestone (CRL) and analyze the stability of surrounding rock during the tunnel excavation. Firstly, using the quartz sand, barite powder, cement, gypsum powder, calcareous sand, coral sand, coral debris, and water as raw materials, four types of CRL similar materials are developed based on its mechanical parameters and the BP neural network inversion method. Secondly, physical model tests are conducted to assess displacement and stress variations during tunnel excavation in the CRL stratum and ordinary stratum, with a focus on the influence of CRL pore structure on the stability of the surrounding rock and deformation failure in the excavation zone. Finally, the numerical simulation of tunnel excavation is carried out to explore the overall impact of the CRL pore structure on the stability of the surrounding rock during tunnel excavation. Results show that: i) The developed materials satisfy the strength and structure characteristics of different types of CRL. ii) The presence of the CRL pore structure leads to a faster rate of rock displacement and stress change, with both the displacement and stress release rates being higher than those of the ordinary stratum. (iii) When tunnel excavation passes through the soft and hard interbedded CRL, the significant deformation occurred in the soft rock and compression failure is prone to occur at the interface between soft and hard rock. iv) The pore structure not only affects the strength of the rock mass but also makes the rock mass more prone to failure. This study provides important insights for underground engineering in marine environments.