Model test and numerical simulation research on the mechanical response law of lager span and small interval tunnels constructed by CD method

In order to study the mechanics response law of lager span and small interval tunnels during the construction process, this paper took the Jinan Southeast Second Ring Engineering-Daling Tunnel as the research object, and developed a large-scale 3D visible and assemble geomechanical model test system. Based on that, we carried out a model test and numerical simulation of the construction progress of the Daling Tunnel, and we studied the mechanics response law by monitoring the deformation and stress changes of the surrounding rock in real time. Combined with the results of the model test and the numerical simulation, the mechanical characteristic response law of the construction process of the lager span and small interval tunnels was revealed, and we found that: 1) The deformation of the surrounding rock of the lager span and small interval tunnels showed a change law of “slow settlement-rapid settlement-tending to be gentle”. And the stress release of surrounding rock shown a change law of “load accumulation-load release-tending to be stable”; 2) The excavation of the section ③ caused the largest settlement of the vault surrounding rock, which accounted for about 18.5% of the settlement value. The order of the influence degree of the surrounding rock deformation of the vault was ③＞②＞④＞①, which were almost the same with the law of the stress release of the surrounding rock; 3) The excavation of the tunnel ② caused the largest convergent deformation of the surrounding rock of the side wall, accounting for about 26.4% of the total convergent deformation. The order of the degree of influence of excavation on the deformation of the surrounding rock of the side wall was: ②>④>③>①, which were almost the same with the law of the stress release of the surrounding rock. The technical methods and conclusions formed in this experiment have important guidance and reference significance for related projects.