Abstract: To ensure the safety of the highspeed culvert when a shield tunnel section of Guangzhou metro crossing underneath pile foundations of a highspeed culvert in upper soft and lower hard limestone strata, three reinforcement schemes are selected, and the reinforcement scheme of oblique jet grouting pile + raft board + composite foundation is adopted. The threedimensional finite element is used to calculate and predict the settlement of the bridge pile foundation, and the results are compared with monitoring data. The theoretical calculation analysis and construction monitoring results show the following: (1) The multiangle and omnibearing jet grouting can effectively avoid existing pile foundations, and controlling the mud discharge volume, ground pressure, and the foundation settlement induced by jet grouting can effectively reduce the influence of reinforcing construction on culvert foundation piles. The measured settlement of the culvert cap is 8.04 mm. (2) During shield tunneling, the measured total settlement of the culvert cap is 10.87 mm, which is within safe and controllable range, resulting in normal traffic of highspeed viaduct and culverts.

Key words: shield tunnel, karst, upper soft and lower hard strata, oblique jet grouting pile, culvert pile foundation, ground reinforcement