Sealing under artesian circumstances to stop water causing collapse

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Many geotechnical surveys are conducted each year, and sometimes total soundings cause artesian leaks. Minor leaks can be successfully sealed with bentonite rods pushed into the hole by a wooden pole. However, artesian leakage with high flows can be very difficult to seal. The consequence of a leaking borehole can be severe, especially if it is not discovered in time and particularly if the water flow causes erosion within the soil. Undiscovered sink holes can be dangerous for the public and the landscape can suffer detrimental changes due to the water flowing up through the ground. NPRA report nr. 704 “Sealing leaking boreholes with grout” (2021) describes how Norwegian Public Roads Administration in 2018-2019 conducted a research program where one of the aims was to find a practical and robust method for sealing leaking boreholes caused by total soundings, with the same drilling equipment that penetrated the artesian aquifer in the first place. Drilling mud of bentonite and barite was tested but failed, since the resulting gel did not sustain the pressure over time. Instead cement for underwater repair works was grouted directly into the leaking formation. Huth & Wien Engineering AS (HWE) has used a one-component water reactive polyurethane grout to seal against artesian water pressure at several locations in Norway. The first time was in 2015, when a total sounding for new Rv. 23 in Linnes, Lier, had penetrated a layer with artesian pressure below 18 m of quick clay. The sealing with polyurethane was successful and took less than two days to perform. Several other projects with leakage due to artesian pressure have since been sealed with this method. This paper describes some of these cases, presents the success criteria, and problems encountered. It can be concluded that successful sealing of leakages due to artesian pressure, can be performed by grouting with polyurethane. There is a correlation between the time after puncture and the effort needed to seal the borehole. Leakages that have been difficult or impossible to seal will be presented, together with plausible explanations. Such examples are usually more interesting, and an analysis can be used to improve of the planning and execution of the sealing.

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