Abstract: To improve the construction accuracy and quality of largediameter metro jet system(MJS) vertical reinforcement under a low clearance, a case study is conducted on the Airport T1~T2 Section on the XintangBaiyun AirportGuangzhou North Railway Station of Intercity Railway in Pearl River Delta, and construction technologies are introduced. First, according to the project overview and geological conditions, the undercrossing scheme and the soil prereinforcement arrangement are determined. Then, the construction challenges and essential construction control technologies are studied specifically. Finally, the reinforcement effect is comprehensively examined from three aspects: pileforming quality, structural displacement, and benefits evaluation. The research results show the following: (1) By transforming the lifting device system, the reinforcement construction can be realized under low clearance, thus greatly improves the construction adaptability. (2) The speciallydesigned alloy drill head and the level can realize poreforming with high precision, and the highpressure grouting system can realize the highquality pile with large diameter. (3) The improved MJS process not only ensures the reinforcement effect, but also effectively avoids underground obstacles and pipelines, and its microdisturbance effect also ensures the normal operation of the underground passage during construction.

Key words: shield undercrossing, low clearance, metro jet system vertical reinforcement, pileforming precision, microdisturbance, equipment modification