Reducing Environmental Impact of Rock Mass Grouting Through Real Time Data Analysis-Paper

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Pre-excavation grouting (PEG) is essential for controlling water inflow in tunnels, but cement production makes it a major source of greenhouse-gas emissions. In Norwegian urban tunnelling, cement used for PEG can generate emissions equivalent to the annual CO₂ output of 15 people for every 100 metres of tunnel. High-pressure grouting can seal fine or clay-filled fractures, but applying it indiscriminately may cause hydraulic jacking and excessive grout consumption.<br /><br />Research cited in the paper found signs of hydraulic jacking in 23% of 3,391 grout holes. It also found that microfine cement (MFC) used about 50% less grout than ordinary Portland cement (OPC), without reducing the likelihood of meeting water-inflow requirements. However, grouting is difficult to predict, and conventional data logging—often at intervals of 10 seconds or more—may be too slow to reliably identify jacking or guide decisions during operations.<br /><br />The Logic Grouting project is developing tools for high-resolution, real-time analysis of grouting data. Online visualization of pressure, flow and grout consumption, combined with measurement-while-drilling data and digital geological mapping, can help engineers adapt grout type, pressure and stop criteria to local conditions. Acoustic-emission sensors are also being investigated, although their effectiveness depends on rock conditions and they are not considered suitable as permanent monitoring tools.<br /><br />A hypothetical case study illustrates the potential benefits. By identifying probable jacking early and adjusting the grouting procedure in selected holes, estimated cement use and CO₂-equivalent emissions fell by about 26%. The authors emphasize that real-time analysis could also reduce construction time and costs while maintaining adequate control of groundwater inflow.

Keywords

pre-excavation grouting

tunnel water inflow

greenhouse-gas emissions

hydraulic jacking

microfine cement

ordinary Portland cement

real-time data analysis

grout consumption

Norwegian urban tunnelling

groundwater control