Mechanical behaviour of conditioned material for EPBS tunnelling

The rapid growth of the development of the cities all over the World, brought the necessity of bringing deeper the services and all the activities which are not strictly necessary above the ground like houses. This sudden demand of new tunnels obliged to push the excavation industry towards mechanized methods which allow to avoid settlements on the surface, where other structures and infrastructures are located. In this context EPB shield machines play a crucial role, as with a good control of this technology, a tunnel can be excavated basically everywhere, also below important structures. This implies the perfect knowledge of the geology but especially requires a precise study of the soil conditioning, in order to allow an effective counterpressure to the front. The development of preliminary laboratory tests, which means before the tunnel project starts, allows to assess the best conditioning set for each lithotype which can be encountered during the excavation. These tests are performed at room pressure, nevertheless recently the main goal is to study the conditioned mass at pressure conditions which can be found in an excavating chamber, which might influence the state of the mass itself. The aim of this work is the development of new techniques which can exactly reproduce this state, through the use and modification of techniques proper of the geotechnical engineering (shear and triaxial tests) and the design of new devices able to underline these aspects in detail. The new approach includes, as well as the consideration of a certain pressure condition, also the definition of an undrained condition used for testing, which allows to keep the conditioned mass in its original state for its study.