During the sequential excavation of the double-line shield tunnel near the existing bridge pile foundation, the deformation mechanism of the interaction between the pile, soil, and tunnel is still not well understood. Moreover, the traditional model testing method is incapable of directly displaying the deformation of the internal soil, which hinders the accurate interpretation of the influence mechanism of the pile foundation during shield construction and the effective risk control. To solve these problems, this study aims to investigate the dynamic interaction between the tunnel, pile foundation, and soil under the sequential shield construction conditions.

Based on the actual engineering case of Chongqing Rail Transit Line 15, a transparent soil model test with a geometric similarity ratio of 1:200 was established and combined with particle image velocimetry (PIV) technology to study this issue. In the experiment, the sequential excavation process of the double-line shield tunnel near the bridge pile foundation was simulated, and the displacement field of the soil was captured and analyzed using high-speed imaging combined with the PIVlab software.

The experimental results show that compared with the single-line tunnel construction, the settlement curve of the foundation during the double-line shield construction presents an asymmetric “V–W” type evolution pattern (where “Ⅴ-type” refers to the symmetrical single-peak settlement pattern centered on the arch crown of the preceding tunnel after single-line shield excavation; “W-type” refers to the asymmetric double-peak settlement pattern formed by two settlement peaks at the arch crowns of the preceding and subsequent tunnels respectively, with relatively smaller settlement of the middle soil column after subsequent tunnel excavation). In addition, the response of the existing bridge piers and the surrounding soil occurs with a noticeable delay during shield advancement. The maximum increment of soil settlement and bridge pier inclination occurs when the shield machine advances to a position that is 0.5–1.0 times the tunnel diameter away from the bridge pier section. The sequence of settlement values for the characteristic points is as follows: the arch top of the subsequent tunnel, the middle soil column, and the arch top of the previous tunnel.

The findings of this study indicate that the deformation of the existing bridge piers and the surrounding soil lags behind the advancement of the shield. The most severe deformation stage occurs 0.5–1.0 times the tunnel diameter after the shield passes through the bridge pier section. The subsequent excavation will exacerbate the influence of the preceding tunnel on the deformation of the existing bridge pier. These findings establish a theoretical basis for the monitoring, risk management, and structural protection of similar engineering projects.