Investigating High-Strength Expanded Polystyrene (HS-EPS) as yielding support elements for tunnelling in squeezing ground conditions

Abstract

Abstract Tunnelling conditions characterized by large and long-term deformations demand yielding support elements as a part of the shotcrete lining. The yielding support elements transform radial displacements into a tangential closure without compromising the lining system's support capacity and avoiding micro-cracking and overstressing of the shotcrete during the curing process. While products available on the market are satisfactory in performance, they are often heavy, difficult to handle on-site, and hence time-consuming for installation. A novel lightweight yielding support element made out of High-Strength Expanded Polystyrene (HS-EPS) is introduced to overcome these operational drawbacks. Unconfined compression tests on small- and large-scale samples were carried out to investigate the HS-EPS strength and deformation characteristics. Further, the combination of several HS-EPS panels with different stiffness properties allows the specific design of a yielding support element with optimum stress–strain behaviour for minor to severe squeezing conditions. Finally, deformation analyses with stress–strain curves and Digital Image Correlation (DIC) were carried out, and suggestions for the practical application on-site are given.