PSI - Issue 32

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A.K. Fedoseev et al. / Procedia Structural Integrity 32 (2021) 202–208 A. K. Fedoseev/ Structural Integrity Procedia 00 (2021) 000 – 000

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If maximum propagation radius of grouting material is less than fault zone extension drilling of additional pumping boreholes could be necessary. In that case harsher scenario takes place when maximum pressures at the WPS top are maintained over the whole length of flaw zone (Fig.1b). If the fault area boundary touches an aquifer border it is possible that the grouting mortar will infiltrate this zone. As it is practically impossible to determine permeability of the freshly formed fault area it is necessary at least to try to estimate its feasible limits. An obvious choice for the lower limit is of course a zero permeability of the fault zone in WPS which complies with aforementioned problem statements (Fig.1a, 1b). As for the upper limit it seems reasonable to assume the permeability of failure zone to be the same as overlying aquifer. Otherwise, if the fault area permeability is higher, it means that low saturated brines from overburden will be driven into the fault zone which in turn could lead to intensification of salt rock dilution and expansion of that zone. That kind of situation has an irreversible pattern and trying to save potash mine using the chosen method no longer makes sense. Bearing all this in mind the proposed problem statements should be supplemented with variants that account for the possibility of grouting material infiltration under pressure into faulted area in WPS (Fig.1c, 1d). The change of pressure with distance from tamping wellbore is determined by the same relations. 3 Application example The proposed methodical approach was applied to the situation around salt exploration well number 492 at the area of blocks 4 and 5 of 3rd south-east panel in south-east part of BKRU-4 mining field (Berezniki, Russia). In this area two sylvinite layers (AB and KrII) have been mined since 2000. Altitude is 160 m, mining depth is around 280 m. The significant increase in subsidence rate (from 50-60 mm/year in 2102 to 153 mm/year in 2013) was registered there in 2013 and next year it went up to 1400/year.

Fig.2.Fault areas distribution at the beginning of 2021 according to geomechanical calculations