Model Experimental Investigation Of The Face Stability Analysis Of Tunnels In Sand

Subway construction has entered a rapid development period in recent years,with more and more tunnel construction, application of shield machine has becomethe principal means. However, there are more and more face collapses during theprocess of tunneling excavation, so the face stability study is still the major topic atthe present stage or in future in tunnel engineering research.The paper studied the dry sand tunnel face stability by1g model test andtheoretical study and the comparison of practical engineering to evaluate with ParticleImage Velocimetry. The main contents include the following aspects:(1) Use the principle of particle image velocimetry in hydrodynamic, a MPIVimage processing program based on MATLAB platform is developed. And introducedthe image processing principle and process of PIV in detail, introduce the workingprinciple of MPIV program including the parameter setting, it is to provide supportfor the model test results analysis.(2) Combine with the characteristic of MPIV to design a non-contactmeasurement model box (shield diameter is10cm) and PIV test system, excavationface stability tests respectively with the depth ratio of0.5to5.0is studied. With theprinciple of symmetry for model box design, it is to achieve non-contact measurement,and simulate the instability of excavation face by the control of piston displacementmethod.(3) Accomplish the maximum settlement-piston displacement figure is presented,the soil displacement field plots of the front face soil. Research on the influence ofdepth ratios to the surface settlement laws and the how the soil arching affectsworking during the soil deformation process, the face failure modes under differentconditions of depth ratio according to the displacement field is determined.(4) According to the face failure pattern from model tests, on the traditionalthree-dimensional wedge body which based on limit equilibrium method, an three-dimensional wedge body model in dry sand is proposed, and derive it’sexcavation face ultimate supporting force calculate formula, comparing andvivificating with the project of Beijing subway line6.From the experimental results, it shows that during the face instability thesurface displacement experienced four stages from no displacement to collapse. Andin the same way, the soil arching also divides in four stages from soil archingincipience to disappearance. Showed by the displacement field, the mechanism oftunnel face instability is like basin to chimney, and the new dry sand three-dimetionalwadge body model can predict the face supporting force good, and can be thebenchmark of practice project.