Analysis of construction impact and safety evaluation of metro shield tunnel under-crossing existing bridge pile foundation

With the continuous development of urban underground space development, shield tunnel engineering inevitably intersects with existing traffic trunk lines, municipal pipe networks and buildings in the construction process, and often faces many difficulties, such as sensitive response of surrounding environment to construction disturbance, serious consequences of risk accidents and so on. Based on practical engineering, this paper conducts the following research: (1) Numerical simulation analysis of subway shield tunnel construction under existing bridge pile foundations is carried out to preview various mechanical responses during the construction process; (2) A scientific safety evaluation system and classification standard for the construction of subway shield tunnel under the existing bridge pile foundation are constructed. At the same time, the combination evaluation method of AHP-Entropy weight method and TOPSIS method based on game theory is used to evaluate it, and it is concluded that the risk level of the construction scene is grade III; (3) Numerical simulation is used to verify the scientificity and effectiveness of four safety measures: pre-grouting reinforcement of bridge pile foundations, pile foundation active underpinning, compensation for strength of pile foundation, and replacement of steel segments. Combined with practical engineering analysis, it is concluded that the optimal safety measure for this construction scenario is the replacement of steel segments.