TECHNICAL | MECHANISED TUNNELLING
Top left, figure 8: Conventional grout @T24hrs after 15 strokes on Hagermann table
Top right, figure 9: Conventional grout @T28days at room temperature
Bottom left, figure 10: The new grout solution @T24hrs after 15 strokes on Hagermann table. Improved rheology & no cracks
Bottom right, figure 11: The new grout solution @T28days at room temperature. Improved durability, no segregation
Logistics and procurement:
● Single powdery material ● Constant product quality with no fluctuations on quality
● One supplier, one point of contact for site technical support
● One supply contract
ROLE OF FREE WATER Free water in backfill grout methods is very much linked to water volume losses in the surrounding grounds. A critical argument for water volume losses is how
much water is bonded in each component of the mix and, reversibly, how much water has a critical volume loss potential. Free water in conventional backfill grouts goes to more than 70%, a huge factor that impacts durability, affecting shrinkage and permeability of the final product. In the new grout method there is significantly less free
water in net volume (overall 5% – 10% range, regardless the higher water/binder ratio).
50 | Summer 2024
Figures 4 and 5 show the different ratios between
raw materials in conventional grouts and the new grout. Thanks to the high volume of inert aggregates, the binder is bonded in the solids and the aggregates are bonded in the water, reducing the net volume of free water. Figures 6 and 7 show the different volume of free
water in conventional grouts and the new grout. In these conditions the net unbonded free water is better stabilized, leading to a much better and more durable final product; anti wash-out properties are improved after gelling; leaching and shrinking are almost erased; and, early strength contributes to tunnel lining stabilization. How much water can potentially leach will heavily depend on the surrounding ground’s porosity and water content.
PROPERTIES COMPLIANCE WITH TECHNICAL PARAMETERS In addition to the consistently reduced CO2
footprint emissions per m3
carbon , pre- and post-injection
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