Squeezing loading of segmental linings and the effect of backfilling

Overstressing of the segmental lining is one of the major hazard scenarios related to shielded TBM tunnelling in squeezing ground. The present paper deals with this specific problem, addressing the key question of the ground pressure acting upon a segmental lining installed behind a single shielded TBM. Starting with a structured discussion of the influencing factors and their interactions, the paper investigates how the type, location and thickness of the backfilling play an important role with respect to the loading of a segmental lining. Secondly, it explains how to take due account of the actual thickness of the backfilling (which is not known a priori since it depends on the deformations of the bored profile) in a numerical simulation. Thirdly, the paper advances a number of theory-based decision aids which cover the relevant range of ground parameters, initial stress, segmental lining and backfilling characteristics, thus supporting rapid initial assessments of the ground pressure acting upon a segmental lining and making a valuable contribution to the decision-making process.

► Structured discussion of the factors influencing the loading of a segmental lining.
► Numerical simulations which take account of the actual thickness of the backfilling.
► Dimensionless nomograms for the assessment of the loading of a segmental lining.