Tunnelling and geotechnics: new horizons

TLDR

Recent advances in tunnelling theory and practice, including model studies, field measurements, and analyses of time‑dependent ground movements, highlight the critical link between tunnelling and geotechnics and the influence of soil permeability and pore pressure on post‑tunnelling deformation. The lecture presents simplified plasticity models, pilot‑tunnel validation, earth‑pressure‑balance tunnelling advances, and fibre‑optic distributed strain sensing, along with a new design approach for pipeline settlement that accounts for soil stiffness reduction due to tunnel volume loss. Case studies demonstrate that directional drilling can install curved grout tubes for compensation grouting in granular soils, and that a design approach incorporating soil stiffness reduction improves pipeline settlement predictions.

Abstract

New developments in both the theory and the practice of tunnelling are covered in the lecture. The important relationship between tunnelling and geotechnics is highlighted, and recent advances in research and practice are described, drawing on model studies, theoretical developments and field measurements from case histories from around the world. Simplified plasticity models are presented that can be used by designers to assess ground movements and tunnel lining loads in complex ground conditions. The important role of pilot tunnels and in situ measurements to validate such models, drawing on a case history from Bolu, Turkey, and on other tunnelling projects, is described. Recent technical advances in earth pressure balance tunnelling are considered, illustrated by measurements from the Channel Tunnel Rail Link project, with emphasis on key factors influencing volume loss, such as face pressure, soil conditioning and effective screw conveyor operation. A recent case history in Bologna is described, in which the innovative use of directional drilling to install curved grout tubes was employed for a compensation grouting project in granular soils. Time-dependent ground movements and tunnel lining distortions occurring after tunnelling are discussed, their magnitude depending on the relative permeability of the tunnel lining and soil, the degree of anisotropy of the soil permeability, and the initial pore pressure prior to tunnelling. The effects of tunnelling-induced settlements on pipelines are considered, drawing on centrifuge tests and analytical solutions, and a new design approach is presented, taking into account the reduction of soil stiffness with increasing shear strain as a result of tunnel volume loss. The lecture concludes with a description of a distributed strain sensing technique using fibre optic technology, based on Brillouin optical time domain reflectometry (BOTDR), and its innovative application to field monitoring of a masonry tunnel subjected to new tunnel construction beneath it.