MECHANISED TUNNELLING | TECHNICAL
Left, figure 12:
Section through a sample of the new backfill grout
technical performance of main parameters can still be ensured with the new backfill grout solution. These are:
● Ensured pumpability, flowability and stability of Component A
● Very limited bleeding of Component A @T24hrs ● Sodium silicate with low solid content dosage as Component B
● Limited shrinkage @T24hrs for reduction of free water and leeching capacity
● Fewer cracks, improved waterproofing and increased durability
● No segregation, allowing the new solution to be compatible with any ground
● Improved anti wash-out properties
Also, an interesting experiment was carried out to test conventional and new grouts by applying shear stresses on the flow table. Figures 8 and 10 show the two different grouts after 15 strokes on the Hagermann table immediately after mixing Component B. Figures 9 and 11 show the same grouts after 28 days curing at room temperature. The new grout shows excellent thixotropy, improved
rheology with no cracks and no segregation, leading to a better durability.
CO2
CARBON FOOTPRINT EMISSIONS SOURCES OF INFORMATION When calculating GWP, it’s important to list the source of information on CO2
credibility to the work. GWP needs also to be formally stated in the Environmental Product Declaration (EPD), drafted in accordance with EN15804+A2 & ISO14025/ ISO21930 standards. Generic (global) dataset from Ecoinvent 3.6, Generic
(European) dataset from CEPE database v3.0 (2016) and EFCA Model EPD: EPD-EFC-20150091-IAG1-EN (Europe) are just some of these sources.
CONCLUSIONS The sustainable backfill grouting technology discussed is a brand-new solution designed to work in the industry for very long time. This new product is compatible with the new ‘Green
TBM’ concept but also with any type of TBM currently serving the market. The benefits are particularly advantageous for the
environment, in terms energy and water reduction, and carbon footprint emissions. The advantage of the new technology of backfill
grout matches with the constant increase of the internal diameter of final tunnels (tunnel ID) that leads to a corresponding increase of the volume of chemicals to be used during TBM operation. With this backfill grouting technology, contractors
have a variety a selection of potential benefits to employ on projects, such as: a new way to approach protection of the environment (reducing CO2
emissions
by 40%-60% and less leaching into groundwater); benefits to themselves and operators (less risk of secondary grouting, able to stick with existing plant, reduction in logistics and mixing, and costs comparable to conventional backfill grouting solutions); and for employers and end users (increased durability, and less chance of water ingress and so fewer repairs).
carbon footprint emissions to give
REFERENCES 1 Wolfgang Aldrian, Tunnelling Journal, April-May (2021).
2 EFNARC, “Specification and Guidelines for the use of specialist products for Mechanized Tunnelling (TBM) in Soft Ground and hard Rock” (April 2005).
3 EN15804+A2 & ISO14025/ISO21930 standards. 4 Ecoinvent 3.6 “Generic (global) dataset” (2022). 5 CEPE database v3.0 “Generic (European) dataset” (2016). 6 EFCA Model EPD “EPD-EFC-20150091-IAG1-EN (Europe)” (2022)
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