Effects of advancing tunnel on a loaded pile: Numerical analysis and field measurements

A full-scale research study was conducted during the bored tunnelling of the Klang Valley Mass Rapid Transit - Putrajaya Line beneath an existing building structure in Kuala Lumpur, Malaysia. The primary objective was to investigate the tunnel-soil-pile interaction at various stages of tunnel excavation. This study combined field measurements and three-dimensional (3D) numerical analysis to understand the transient effects of TBM tunnelling on a loaded pile. An experimental pile was instrumented with vibrating wire strain gauges, an inclinometer, and distributed fibre optic sensors using Brillouin optical time domain analysis. The pile was pre-loaded and continuously monitored in real-time throughout the tunnel construction process. The 3D finite element modelling was used to simulate the pile’s transient responses based on actual tunnel boring machine (TBM) driving data. The study revealed that the zone of influence due to tunnelling effects extended from y = −2 D to y = 4 D , with the peak effect observed at y = 1 D to 1.5 D , where D represents the tunnel diameter. The analysis of axial load patterns highlighted transient responses, including tensile loads below the tunnel invert, which propagated upward and subsided due to negative skin friction. The maximum downdrag load observed reached 56%–71% of the pile’s working load. Additionally, pile movement patterns indicated outward deflections as the TBM approached and a return toward the tunnel post-passage, aligning with the predicted behaviour in a negative face loss scenario. This validated numerical framework provides a solid foundation for further parametric studies and enhances the understanding of tunnel-soil-pile interactions.