Analysis of Grouting Stability in Composite Stratum Tunnels with Discontinuity Layout Optimization

When constructing tunnels in composite strata of soft and hard rock combinations, the disturbance during construction often leads to the collapse and instability of weak strata. Pregrouting is commonly employed in tunnel construction to reinforce the weak surrounding rock, aiming to achieve stable excavation faces. The assessment of excavation face stability and the selection of grouting parameters are crucial for the safe construction of tunnels in composite strata. This paper utilizes the recently proposed discontinuity layout optimization (DLO) method. Taking the tunnel at the Shilaoren Bathing Beach Station in Qingdao as an example, the stability of the excavation face is quantitatively evaluated using a safety factor. Furthermore, the paper explores the influence of the position of the composite stratum boundary, friction angle, cohesive strength, and grouting parameters on the stability of the tunnel excavation face. Simultaneously, the paper fits the grouting parameters and safety factor curves under different geological parameters, aiding construction personnel in choosing reasonable grouting parameters.