Under the conditions of karst development and soft upper and hard lower strata, the ground settlement control of tunnel under airport taxiway construction is stricter than that of ordinary tunnel. Tunnel construction methods and karst disposal measures are also particularly important. It is an engineering problem that needs to be solved urgently to ensure the safe passage of the tunnel under airport taxiways without suspension. Taking the intercity railway tunnel under the taxiways T3 and T4 of Guangzhou Baiyun International Airport as the research object, this study carried out theoretical analysis and field test on Karst Treatment Measures and surface settlement control measures. The Karst Treatment Measures under different condition and the "Pile Supporting Plate" structure system are proposed to support the taxiway. The effect of the system is analyzed by numerical method, and the on-site surface settlement is monitored. The research results shows that the maximum settlement of T3 and T4 taxiway surface monitored on site are 5.90mm and the differential settlement is 0.12‰. The numerical simulation results are similar to this value, and do not exceed the settlement control standard of taxiway. Through the research, the key technologies for the construction technique of tunnels under airport taxiway of airport taxiway under tunnel in karst area and upper soft and lower hard strata are is formed, the karst disposal measures for tunnel construction in karst areas is summarized and the "pile support plate" protection system for ground settlement control when tunnels under pass the airport without suspension is proposed ,which can provide reference for similar projects.

This study addresses the contradiction between the strict requirements of vibration speed control in existing operating tunnels and the difficulties of tunnel excavation in hard rock strata, as well as the lack of theoretical basis for blasting vibration speed control standards in adjacent tunnels. Based on the energy principle, this study establishes the energy balance equation in a single cycle of the low frequency band of blasting vibration wave curve, and proposes to replace the maximum elastic strain energy accumulated in concrete by twice the kinetic energy corresponding to the peak vibration speed under blasting action (the "Twice the Peak Kinetic Energy Method") according to the conversion relationship between the input energy of concrete mass unit and the elastic strain energy and kinetic energy. On the basis of this method, the formulae of safe vibration velocity of blasting in two states were derived by combining the energy criteria corresponding to the damage and destruction states of concrete. It is verified in a new tunnel under existing operating railway section in hard rock stratum in Xiamen area. The results show that the maximum principal stress and displacement reach the maximum value in the cycle when the peak vibration speed decays close to zero for the first time in the low frequency band; the elastic strain energy also reaches the maximum value in the cycle when the kinetic energy decays close to zero; affected by a small amount of dissipation energy, the kinetic energy corresponding to the peak vibration speed is slightly less than twice the maximum elastic strain energy, which verifies the reasonableness of the theoretical analysis. Finally, the safe vibration speed corresponding to different concrete grades is given based on the design value of tensile strength.