Undrained behaviour of granular soils conditioned for EPB tunnelling – A new experimental procedure [Undräniertes Verhalten von grobkörnigen Böden für Vortriebe mit EPB-Schilden – Ein neues experimentelles Verfahren]

This paper presents a characterisation campaign carried out on granular soils conditioned for EPB tunnelling using a modified direct shear box. The main objective of soil conditioning is the reduction of its shear strength to control the counterpressure inside the bulk chamber. In order to preserve the pseudo-fluid characteristics of the conditioned soil mass, the main concerning para meters are their undrained properties. To characterise the un drained behaviour an adopted watertight direct shear apparatus was used. The purpose of this research is to define a simplified testing procedure for conditioned soil, analysing its feasibility and reliability with resources that can be found at any laboratory or job site. A comparison between the results obtained under dry and conditioned conditions is presented for three different cohesionless soils. The choice of the materials studied has been made in order to cover a wide range within sands grain size.