Instability determination and construction monitoring analysis of shield excavation face in diorite-bearing strata

The stability of the excavation surface is directly related to that of the surrounding rock of tunnels and the influence level of disturbance deformation of strata, which is the key issue to the shield construction technology. For the shield tunnels excavated in diorite strata, due to different weathering degrees of the rock mass, it is more difficult to judge and control the stability of the excavation surface. Relying on the tunnel project between the Long-Distance Bus Station and Shengchan Road Station of Jinan Rail Transit Line R2, and aiming at the difference of stratum properties caused by the uneven weathering of diorite, the main influence parameters of support pressure of the excavation face under different lithology occurrence conditions and the influence range of its determination instability are studied through numerical analysis and field measurement. The following conclusions are drawn: (1) For the single stratum, the internal friction angle has the most significant effects on the ultimate support pressure, followed by elastic modulus and cohesion, while the Poisson's ratio and unit weight have the least effects. (2) For the composite stratum, if the stratum with poor self-stability accounts for a larger proportion of the tunnel excavation face in the vertical direction, the limit support pressure will be affected more obviously. (3) The limit support pressure is only related to the stratum parameters within the excavation face. No matter how the stratum parameters outside the excavation face change, the limit support pressure is little affected. The above results have a good guiding role and reference value for the design and construction of shield tunnels in weathered uneven diorite strata or similar strata.