Fill behind lining segments in tunnels excavated by tbm (full face boring machinery)
Mechanically excavated tunnels in rock or rock masses with high convergence (i.e. where the rock has a strong tendency to expand, thereby reducing the cross-section excavated) require special care at the design stage and during construction, to ensure that there is no excessive thrust from the rock on the tunnel lining segments.
This phenomenon can be kept under control by inserting a “collapsible” material between the rock mass and the lining. The material used must be sufficiently rigid to ensure that the tunnel lining ring remains stable, but must also be able to collapse when a predetermined level of stress is reached, deforming plastically to reduce the thrust on the lining.
Laterlite Expanded Clay is ideal for this type of application because:
This process was developed for the Gran San Bernardo Tunnel under the Alps, between Italy and Switzerland, and won the Best Technological Solution of the Year award at the 2012 World Tunnel Congress.
Other fill types in tunnels
Expanded clay is widely used to fill various types of cavity between the rock and the lining of new and existing tunnels, whether or not the rock is convergent.