The Boreability Evaluation Of TBM Tunnelling Under Composite Strata

TBM integrates many high-tech achievements, such as hydraumatic, machinery and electric etc. It can improve construction efficiency and be widely used. In order to estimate duration, choose machine model and evaluate economical efficiency, it's necessary to do research into TBM construction adaption, especially under composite strata. This paper is to study surrounding rock boreability. The main research contents are:(1) When thrust force reach the critical value, rock will break. Rock-crushing efficiency would prove along with the increase of power. But it need to exclude effect of operating parameter for evaluating surrounding rock boreability. So it's reasonable to define the value of dividing cutter thrust by penetrate rate as boreability index.(2)There are multiple strata in vertical or horizontal direction of tunnel face when encountering composite strata. The relative proportion of soft rock and hard rock have an effect on stiffness and physical properties of ground. So we can define the proportion of hard rock in total thickness as the composite strata index for further research about effect on penetration efficiency.(3)When cutters push against tunnel face, the rock will crack and become into cuttings, then internal and lateral crack will evolve, which produces cuttings. The cutter force could be simplified as a concentrated load, composite strata is equivalent to transverse isotropic body. The equivalent continuum method can be used to deduce the equivalent stiffness. Through the analytical solution for boussinesq problem of transverse isotropic layer the stress distribution can be obtained. Rock crushing area can be deduced according to mohr-coulomb yielding criteria by means of MATLAB programming. After that, we can analyze how composite strata and layer factor affect the penetration efficiency.(4)According to the analytical solution for boussinesq problem, we can analyze how composite strata index and rock strength affect the penetration efficiency. It turned out that penetration efficiency index rose with the increase of rock strength, meanwhile, they appear to be a linear relationship; Penetration efficiency index rose with the increase of composite strata index which present logarithmic relationship.(5)The UDEC model was presented for simulating rock fragmentation process in mixed face ground, calculating how layer factors affect penetration efficiency and comparing with analytical results. A multi-factor forecasting model can be concluded, and then comparing with engineering field data based on Lotschberg Base tunnel and Zagros tunnel.the model is more accurate and concise comparing with others, which have considered the composite strata.