Sudden breakthrough

SUDDEN BREAKTHROUGH of the waters and quick clays (EN: sudden break of the water and quick sand inrush; DE: plotzlicher Wasser- und Schwimmsandeinbruch; FR: irruption brusque des eaux et des terrains mouvants; ES: irrupcion instantanea de aguas y de arenas flotantes; RU: внезапный прорыв) is the increased inflow of the water or loose water-saturated rocks, which are having the quick clay properties, into the mine working; this phenomenon proceeds as the result of the spontaneous or forced destruction of the water-resistant rocks within the mine working.

These sudden breakthroughs are observed most often during the starting stage of the mastering of the water-flooded deposits of the useful minerals (in case of the absence of the preliminary drainage), for example, at the underground mines, namely, during the penetration of the mine shafts, of the near-shaft and preparatory mine workings, and less often during the conducting of the extracting works; at the open-pit mines, these breakthroughs are observed during the penetration of the entrance and incision trenches (usually from the sole, during the unsealing of the pressurized aquifers), and less often during the conducting of the overburden stripping and extracting works (on the account of the superficial waters). The sudden breakthroughs represent the greatest danger during the penetration of the inclined and steeply dipping mine workings. The duration of the sudden breakthroughs of the quick clays amounts to several minutes (less often hours), the duration of the breakthroughs of the water amounts to several days or months. The quantity of the material, which has been ejected, may reach several thousand cubic metres, the yield of the water may reach several thousand cubic metres per hour, which fact causes the partial flooding, siltation, or complete "sealing" of the mine workings (especially of the inclined mine workings) throught the great length (up to hundreds of metres), the "burying" of the mechanisms and machines, the forming of the voids within the massif of the rocks, the forming of the pits or troughs because of the settling on the surface of the earth. The initial large inflows of the water usually decrease rapidly, approaching to the constant value (on the account of the establishment of the hydrodynamic regime), or terminate completely after the exhaustion of the resources of the water, after the filling of the mine workings with the quick clays, or after the achieving of the balance between the forces of the hydrodynamic pressure and the friction of the soil mass along the walls of the mine working.

One of the main causes for the manifestation of the sudden breakthroughs at the underground mines and open-pit mines is the insufficient decrease of the pressure of the underground waters within the soil (within the roof) using the drainage devices (see the "Drainage" article), or the unsatisfactory protection of the mine workings against the water using the barrage devices (see the "Barrage" article). The sudden breakthroughs are also caused by the existence of the high-pressure aquifers or water-saturated loose (weakly cemented) rocks near the roof or soil of the mine workings; by the thinning of the water-resistant layers, which are underlying or overlying these water-bearing or loose water-saturated rocks; by the tectonic disturbances; by the collapse of the water-resistant roof (of the mine working) under the water-bearing rocks; by the penetration under the flooded and silted mine workings, under the exploratory boreholes, under the superficial watercourses and water reservoirs.

The insufficient study of the mechanism of the sudden breakthroughs, and the diversity of the factors, which are causing these breakthroughs, determine the complexity of the forecast for these breakthroughs, and of the development of the preventive activities, especially during the operating of the strongly disturbed water-flooded deposits with the inclined and steep embedment. During the penetration of the mine shafts, for the prevention of the sudden breakthroughs, they use the freezing of the loose sandy rocks or the lowering of the water level, while during the penetration of the horizontal underground mine workings, they use various drainage devices for the decreasing of the pressure of the water within these rocks to the acceptable value (which is determined by the calculations). For the places of the underground mine workings, where may take place the sudden breakthroughs, there are forecasted preliminarily the expected quantity of the material and water, which are ejected, there are being developed the activities for the prevention of the breakthroughs, for the ensuring of the safe conditions for the conducting of the mining works, and also for the remediation of the consequences of these breakthroughs within the mine workings (the plan for the emergency response). Within the underground mines, which are dangerous because of the breakthrough of the waters, there are required the water collectors, which are ensuring the work of the main water drainage installations during at least 8 hours with the normal inflow, and for the local water drainage installations, there are required the water collectors, which are ensuring the work during at least 4 hours with the normal inflow; as the emergency water reservoirs, there may be used the old mine workings. For the remediation of the consequences because of the sudden breakthroughs, there are used the redundant pumps within the central pumping chambers, with the performance of at least of the expected inflow o f the water.