Calculation of process load of deep-buried asymmetric multi-arch tunnels

Deep-buried asymmetric multi-arch tunnels have complex mechanical features such as geometric asymmetry, structural asymmetry and left-to-right load asymmetry. There have been no relevant codes and standards for the process of construction on the pressure evolution of surrounding rocks and load calculation. It is an outstanding problem that the basic theory lags behind on reality in project practice. Based on the calculation of process load and the assumption of the Protodyakonov's theory, the formula for calculating process load of deep-buried asymmetric multi-arch tunnels is derived with synthetical considerations of the asymmetry and the construction process of two cavities of a tunnel as well as the influences of the excavation of the back hole on the increase of the loosening load of the first hole, and the two conditions are compared to see whether the influences of construction process on the load of each part of asymmetric multi-arch tunnel are taken into account or not. Finally, based on specific projects, the derived formula is proved to be valid from practical angle. It may provide a reference for the determination of similar construction schemes and the design and optimization of supporting structures in the future.