<p>This study investigated the bending responses of three instrumented piles during tunnelling using distributed fibre-optic sensors. The measurements reveal the strain distribution along the entire lengths of the piles, and the strain is used to evaluate the bending moment and deflection. In particular, the direction of maximum bending moments is outward from the tunnel and the negative peak bending moment (NPBM) is the maximum value, which is independent of pile-tunnel position (<i>L</i>_pt). Besides, the bending strain energy (<i>U</i>) is used to calculate the amount of energy absorbed from the work done by tunnelling loads which includes the face pressure and the soil-squeezing force produced by the shield body. <i>U</i> and NPBM reach the maximum value at the same pile-tunnel position before the tunnel completely crosses the pile. Two novelty parameters, negative peak bending moment-to-strain energy ratio (NPUR) and the ratio of the strain energy other than the negative peak position to the strain energy at the negative peak position (<i>α</i>), are firstly proposed in this study. They successfully describe the ability of strain energy converting into NPBM and the degree of energy concentration in pile, respectively. Most importantly, negative peak curvature, which can be derived from NPBM, can be utilized to determine the local failure of pile, together with NPUR and <i>α</i>.</p>