When shield tunnel boring machines (TBMs) are used, the outer lining is constructed using pre-fabricated lining segments. In hard rock conditions the required gap between the lining and excavation boundary is backfilled with pea gravel. In this case, designers consider only the backfilled material relevant for the bedding effectiveness. Thus, a sound knowledge of the deformation properties of pea gravel is essential. At present these parameters are determined in non-standardized laboratory or on-site tests. Moreover, no validation of the used parameters is performed in situ. Based on the static load plate test a prototype for the in-situ determination of the deformation properties of pea gravel was designed and manufactured at the Institute of Rock Mechanics and Tunnelling at the Graz University of Technology. The testing device allows for a maximum test stress of 1.50 MPa under the load plate. This research focuses on the development process and the detailed design of the manufactured prototype. The recorded measurement data (force and displacement) allows to calculate the stiffness properties (i.e. bedding modulus, static deformation modulus, stiffness modulus) of the material tested. Radial openings in the lining segments serve as measurement locations. Mounting of the testing device in the tunnel is possible without any alterations in the lining elements or the lining design. Determination of the stiffness parameters is shown using the test data of one exemplary test series.
In mechanized driven tunnels, using single or double shield TBMs (S-TBM/DS-TBM), prefabricated lining segments are used as outer lining. Thereby, the load-carrying rings are assembled within the protection of the shield. Due to the construction method, a gap between lining and excavation boundary (i.e. rock mass) exists after a newly installed ring leaves the shield. This so-called ‘annular gap’ needs to be backfilled using a suitable material in order to allow for load transfer. Ideally, the occurring rock loads are evenly distributed. In hard rock conditions, a fine grained and closely graded gravel, termed as pea gravel, is pneumatically injected through radial openings in the lining. The invert area is backfilled using a pea gravel-mortar-mixture.