Fill the gap
Excavation with shield TBMs means that precast concrete segments are installed to form the tunnel and an annular gap remains between these segments and the ground. The filling of this annulus is a very important requirement as this ensures homogeneous contact with the ground, transfers load from the TBM back-up and also can help to waterproof the tunnel. Sika is actively involved around the world in many tunnelling projects, providing a wide range of products for TBM backfilling according to each project’s specific requirements.
Different types of filling materials have been developed: hydraulically setting mortar and two component grouts. Sika offers a complete range of stabilisers and retarders to prepare the backfilling grout: SikaTard®, Sika® ViscoCrete®, SikaFume® and Plastiment®.
Two component backfilling
Two component injection backfill is prepared by mixing a blend of water/cement, bentonite and retarder (component A) with an accelerator (component B). These get mixed just before the component A is injected through the tailskin and transforms itself from a creamy liquid into a gel in around 10 – 20 seconds. The final mix has comparable compressive strength to that of the surrounding ground and can fill every gap and void before it sets and hardens. For the required flow and retarded set effects, Sika’s Sika-Tard® and Plastiment® products are used. SikaSet® or Sigunit® accelerators are then used to control the setting and hardening time and process.