Rapid and long-lasting bedrock flow-path sealing by a ‘concretion-forming resin’: results from in situ evaluation tests in an underground research laboratory, Horonobe, Japan

A capability to permanently seal fluid flow paths in bedrock, such as natural faults/fractures, and damaged zones around boreholes/excavations, is needed to ensure the long-term safety and effectiveness of many underground activities. Cementitious materials are commonly used as seals, but these materials unavoidably undergo physical and chemical degradation, therefore potentially decreasing seal durability. To solve these problems, a more durable sealing method using ‘concretion-forming resin’ has been developed by learning from natural calcite (CaCO 3 ) concretion formation. The sealing capability of resin was tested by in situ experiments on bedrock flow paths in an underground research laboratory (URL), Hokkaido, Japan. The results showed a rapid decrease in the permeability down to 0.1% of the initial permeability owing to calcite precipitation over a period of 1 year. During the experiment, inland earthquakes occurred with foci below the URL (depths of 2–7 km and maximum magnitude of 5.4). As a result of the earthquakes, the hydraulic conductivities of the flow paths sealed initially by ‘concretion-forming resin’ increased. However, these flow paths subsequently resealed rapidly and within a few months recovered the same hydraulic conductivities as before the earthquakes. This new technique for rapidly producing long-lasting seals against fluid flow through rocks will be applicable to many kinds of underground activities.