Field Observation of Shield Tunnelling and Its Transient Effects on A Loaded Pile

Abstract

A full-scale research study was conducted during the bored tunnelling beneath an existing building structure in the Klang Valley Mass Rapid Transit – Putrajaya Line in Kuala Lumpur, Malaysia. The primary objective of this study is to investigate tunnel-soil-pile interaction at different stages of tunnel excavation. The research involves a combination of full-scale field measurements and numerical analysis, contributing to a deeper understanding of the transient effects of shield tunnelling on existing loaded piles. An extensively instrumented experiment pile, equipped with vibrating wire strain gauges, inclinometer, and distributed fibre optic sensing using Brillouin Optical Time Domain Analysis (BOTDA), was installed, pre-loaded, and continuously monitored in real-time throughout the tunnel construction process. BOTDA is a novel technique for continuous strain measurement, provides inherent advantages over conventional point-based sensors in evaluating three-dimensional pile deformation such bending and axial displacements. The field measurement results indicate that the zone of influence due to tunnelling effects extended from a distance of 2 times the tunnel diameter behind the pile to 4 times the tunnel diameter ahead of the pile, with peak impacts observed at 1.5 times the tunnel diameter ahead of the pile. Continuous strain profiles from fibre optic sensors showed upward forces in the lower portion of the pile, contributing to tensile strains. The maximum tensile load was temporarily sustained before reverting to a compressive downdrag load as the tunnel boring machine (TBM) moved further away. The delayed response, likely occurring upon the dissipation of excess pore water pressure and diminishing tunnel face support pressure. The study elucidates distinct outward movement directions observed in the pile as the TBM approaches, followed by lateral deflection returning towards the tunnel upon TBM’s passage. This validation strengthens understanding of pile behaviour during various tunnel excavation stages, supporting the negative face loss hypothesis.