MECHANISED TUNNELLING | TECHNICAL
Retarder 0%
Bentonite 3% Water 67%
Average conventional backfill 2k grouts Accelerator 8%
Cement 22% 56%
Our new grout 7%
37%
Top left, figure 4: Relation of raw materials in conventional two- components grouts
Cement
Water Retarder Betonite Accelerator
Conventional grouts (Average) Component A + B, 45% Free water 55%
Bottom right, figure 7: Relation between free water and Component A in Sika®
Stabilizer-7100 TBM Component A + B Free water Component A + B Free water Component A in powder Sika® Stabilizer-7100 TBM Water Component B Our new grout Free water 55% Component A + B, 95%
Top right, figure 5: Relation of raw materials in Sika® TBM
Stabilizer-7100
Bottom left, figure 6: Relation between free water and Component A in conventional two- components grouts
Also, conventional logistics, mixing and placement
pose several other operational challenges. In a conventional formulation that includes cement
as binder, water, bentonite, other admixtures as Component A, and sodium silicate as an accelerator of Component B, each item requires its own storage tank on site, with the materials procured and delivered separately by multiple suppliers. They are stored and mixed at the site batching
plant located outside the tunnel. There are many influencing factors that contribute to supply chain complexity and overall quality fluctuations over the duration of a project.
REASONS FOR A NEW SUSTAINABLE, ECO-FRIENDLY FORMULATION In a standard annulus grout, regardless the TBM excavation diameter the average percentage CO2 emission is around 20% - 22% range. Figure 2 shows the CO2
grout per linear meter of tunnel1 The goal for a new environmentally sustainable
formulation is to reach a total impact of 12% - 13% of CO2
emissions in a TBM tunneling project, reducing
the overall impact to half of the current one with conventional grouting methods.
ENVIRONMENTAL OPPORTUNITY Conventional grout formulations contain between 260kg to 330kg of cement in every m³, being responsible for an average of 300kg-340kg of CO2
eq. emissions for every
m³ of injected grout in the ground. In order to reduce CO2
200kg/m3 -220kg/m3 eq. emission to around , the challenges rest in doing so while retaining all the key performance properties
(density, viscosity, bleeding, gel time, strength) and operational parameters (pumpability, flowability, stability leading to no segregation) and, last but not least, keeping the costs within the present range. A significant reduction in cement content and overall CO2 carbon footprint emissions represents an
opportunity as long as negligible leaching by limiting free water and increased durability are ensured. The solution that the new grout has focused on is to use unique admixture technologies, thanks to the mining backfill experience and the adoption of less reactive, inert materials.
HOW SIKA® STABILIZER-7100 TBM WORKS
With the new backfill grout solution, Component A is a combination of binder, inert materials and special admixtures delivered as a single dry powder. Existing equipment and systems can be used for the new grout. On site, the new Component A single dry powder
equivalent for segmental concrete and annulus .
must be mixed with water, pumped into the TBM and then mixed at the injection point with sodium silicate as the activator of Component B, as displayed in Figure 3. The binder and water generate a stronger interbond
with inert materials to reduce free water, thereby reducing leaching, increasing strength, controlling hardening behavior and decreasing permeability. Benefits include:
Batching plant & TBM: ● Smaller batching plant with fewer tanks/silos for less complexity
● No retro-fitting required ● Component A mixing procedure unchanged ● No changes of pipes, pumps, tanks outside the tunnel and inside the TBM
● No changes in the injection points in TBM Summer 2024 | 49
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