Development of similar materials with porous of the coral reef limestone and tunnel deformation failure characteristics analysis in the soft and hard interlayer stratum

Coral reef limestone (CRL) exhibits varying sedimentary facies, rock structures, and lithologies at different depths, posing challenges for island engineering construction. This study investigates deformation characteristics of surrounding rock during tunnel excavation in soft-hard interlayered CRL stratum. A novel method for preparing heterogeneous analog materials with prefabricated pores is developed to simulate soft and hard CRL interlayers. Physical model tests under two working conditions examine displacement and stress variations during tunnel excavation. Numerical simulations are subsequently conducted to verify test validity and assess stratum distribution impacts. Key findings include: (1) Prefabricated pore structures effectively replicate CRL's natural heterogeneity. (2) Upper-soft/lower-hard stratum induces significant vault displacement (2.35 mm) and stress concentration (0.82 MPa) due to soft rock compression. (3) Upper-hard/lower-soft configurations cause pronounced arch foot deformation (3.12 mm) from soft rock yielding under overlying hard stratum. (4) Support systems reduce displacements by 14.8% (lining alone) and 33.3% (combined lining-anchor), with enhanced effectiveness in soft CRL. The integrated experimental-numerical approach provides critical insights for tunnel design in heterogeneous CRL formations, demonstrating that support optimization should prioritize lithological interfaces and stress redistribution patterns characteristic of interlayered systems.