HYDROGEOLOGICAL CONDITIONS FOR THE DEVELOPMENT OF THE OSINOVSKOYE DEPOSIT IN KUZBASS

G. M. ROGOV, G. A. PLEVAKO, D. S. POKROVSKY

Over a large area the Osinovskoye coal deposit is overlain by water-bearing conglomeratic and sandy-clayey deposits of Jurassic age and is characterized by very complex hydrogeological conditions for development (Rogov G. M., Plevako, Solomko, 1964).

When mine workings approach water-bearing Jurassic rocks, sudden inrushes of groundwater into the mines occur; from 1957 to 1968 there were 12 such cases: two in the Kapitalnaya-I mine, six in the Kapitalnaya-II mine, and four in the Kapitalnaya-III mine.

The results of studies and analysis of the geological-tectonic structure, geomorphological, and hydrogeological conditions of the deposit made it possible to distinguish four sectors with different hydrogeological development conditions.

The first sector covers the western and southwestern parts of the deposit, where Jurassic rocks are absent or occur as patches on watershed areas. The sector is characterized by a complex geological-tectonic structure. The western limb of the Shchelkan syncline within the sector is complicated by a number of additional folds and a series of major tectonic faults, often extending beneath the valleys of small rivers. The sector includes the western parts of the mine fields of Kapitalnaya-I, Kapitalnaya-II, mine No. 4, and mine No. 9. The productive rocks are weakly water-bearing. Water inflows to the operating levels of the mines (+310, +230, +140) are low and usually do not exceed 50–100 m³/hour. At present the first levels from the surface have been worked out, and mining operations are being developed on the +40 and −40 levels. With the advance of the mining front and the expansion of caving areas, inflows into the mines increase, especially when the subsidence zones capture the valleys of small rivers and ravines. Thus, 217 m³/hour enters the +140 level of the Kapitalnaya-I mine (the total for the mine is 350–400 m³/hour); at the +140 level of mine No. 9, 100 m³/hour enters (the total inflow for the mine is 120 m³/hour). In the Kapitalnaya-II mine, at the +230 level, water inflows are formed entirely by drainage of groundwater along zones of rupture disturbances beneath the valley of the Talzhina River. Water inflows into the Kapitalnaya-I mine at the +140 m level are due to drainage of groundwater beneath the valleys of the Kandalep, Shchelkan, and Polkanaty rivers. Increased water inflows into worked-out mine workings in many cases complicate work on deep levels, since part of them penetrates through the worked-out seams into active longwalls. Sometimes che-

through old mine workings or directly through shaft mouths, which, as a rule, are driven in river valleys, surface waters penetrate into the mine. This is most often observed after heavy rains and during floods.

The second area occupies a narrow strip of the western limb of the Shchelkanskaya syncline, where it dips steeply beneath the Jurassic rock complex. The rapid increase in the thickness of the Jurassic deposits (from 70–80 to 250–300 m) and the complex tectonic structure have determined its distinctive hydrogeological conditions. In the post-Jurassic phases of tectogenesis, the Jurassic rocks at the lower levels were affected by small disjunctive disturbances and by fracture zones oriented along these disturbances, which developed mainly according to the inherited plan. As a result of tectonic movements in the near-contact zone, the productive and Jurassic deposits proved to be crumpled and weakened. The thickness of the weakened zone often exceeds 20 m.

• Jurassic conglomerates and sandstones in the zone of intensive weathering (down to 100–150 m) and in areas of disturbance zones are characterized by increased water content. Despite the regular decrease in the water content of the rocks with depth, the near-contact fractured collectors at depths of 250–300 m, in most cases isolated from the upper, highly water-bearing part of the section, contain large natural reserves of groundwater and pose a danger when their collapse zones are undercut.

The productive rocks beneath the Jurassic deposits are weakly water-bearing. Specific well yields are 0.01–0.02 at the +100 level, and thousandths and ten-thousandths of a liter per second at deeper levels. Here the mine workings are dry, with the exception of individual disturbances along which dripping is observed.

When development and preparatory mine workings approach to within 6–8 m of the contact with the Jurassic rocks, water inflows increase, reaching 20–40 m³/hour. During coal extraction in the Kapitalnaya-II mine beneath the Jurassic rock complex at the −40 level, the total inflow reached 400–450 m³/hour. After leaving this zone and entering the limits of the first area, it decreased to 100–120 m³/hour.

In the second area, nine sudden breakthroughs of groundwater into mine workings occurred. Three breakthroughs into longwalls 1, 20, and 23 (Kapitalnaya-III mine) occurred in the contact zone at a distance of 15–20 m from the Jurassic rocks, as a result of undercutting water-bearing horizons in the zone of intensive water exchange. Four breakthroughs into longwalls 31, 125, and 51 of the Kapitalnaya-II mine occurred in the area where a large tectonic disturbance, “A–A,” was undercut. Two breakthroughs into longwalls 90 and 31 of the Kapitalnaya-II mine appeared after collapse of the longwall roof and undercutting of water-bearing local fractured zones. In all cases, the inflows reached 100 m³/hour, but within 5–6 hours rapidly decreased to the initial 10–15 m³/hour. The exception was the water inflows into longwalls 1, 20, and 23. Owing to the undercutting of water-bearing sandstones in the zone of intensive water exchange, the magnitudes of the water inflows after the breakthrough did not decrease below 30–40 m³/hour for 6–8 months. Within the limits of the second area, the most complex hydrogeological conditions are noted on the northern limb of the Kapitalnaya-III mine at the +100 level. Here the thickness of the Jurassic deposits does not exceed 150–170 m; consequently, collapse of the longwall roof in the near-contact zone will lead to drainage of groundwater from the upper part of the section. Inflows into the longwalls of the northern limb will reach 100–150 m³/hour and more, and sudden breakthroughs are possible when water-abundant zones in disturbances are encountered.

Thus, in August 1968, in longwall 104 in seam \(E_4\), a major inrush of groundwater from Jurassic deposits was recorded, which halted the section for a long time. Beginning as dripping, within 24 hours the water inflow reached 260 m\(^3\)/h. After several hours it began to decline and after 10 days had decreased to 80 m\(^3\)/h. The distance to the contact with the Jurassic deposits was about 35 m. However, in this area there had been double extraction of the Jurassic formations along two closely spaced seams, \(E_4\) and \(E_5\), which increased the height of the previously formed zone of rock crushing after collapse of the roof of the mined-out seams.

Within the limits of the Kapitalnaya-II, Kapitalnaya-I, and Glubokaya mines at the \(+40\) horizon, groundwater inflows into longwalls do not exceed 15–30 m\(^3\)/h, except for areas with large zones of disturbances affecting the Jurassic rocks. Here one may encounter local water-bearing zones with natural groundwater reserves.

The third area encompasses the central part and the eastern limb of the Shelkan syncline. The thickness of the Jurassic deposits exceeds 300–400 m. The productive and Jurassic rocks occur almost horizontally, while on the eastern limb the dip angles of the rocks are 10–15°. Unlike the second area, here, along with large disturbances, erosion channel-like depressions and incisions in the Paleozoic relief are widely developed; they are often composed of coarse-grained, frequently cemented, water-saturated Jurassic sediments. In addition, because of the gentle eastern limb, the third area has an extensive local recharge area compared with the steeply dipping western limb. The thickness of the weakened Jurassic rocks in the contact zone averages 6–8 m, reaching 20–30 m in individual cases (boreholes 1407, 1404, 1463). In mine workings in the near-contact zone, enormous rock pressure is observed, which prevents approach to the contact line by 4–6 m. Examples are crosscut 40 bis and the ventilation drifts of longwalls 271 and 263.

Within the third area the Kapitalnaya-I mine is in operation, and the main promising areas of the Osinovskoye deposit are located there. Water inflows into mine workings are associated exclusively with Jurassic deposits. Water manifestations are observed in workings driven close to the contact with the Jurassic deposits, especially after subsidence of longwall roofs. Longwalls situated in the axial part of the Shelkan syncline and in depressions in the Paleozoic relief are characterized by increased water abundance. Water inflows into longwalls in this part reach 40–80 m\(^3\)/h (longwalls 208, 185, 266, 274, 271, etc.). Water abundance increases sharply when longwalls encounter tectonic disturbances extending into the Jurassic rock complex. In longwall 271, confined to depressions in the Paleozoic relief and encountering a minor disturbance, an inrush of groundwater of up to 500 m\(^3\)/h occurred. High water inflows into longwall 274 (50 m\(^3\)/h) were also associated with a disturbance zone.

Water inflows into the Kapitalnaya-I mine in the third area (horizon \(-60\)) amount to 100–120 m\(^3\)/h, which does not exceed 30–35% of the total water inflow into the mine. From 1953 to the present, inflows into the mines of the Osinovskoye mine field, owing to development of the deposit beneath Jurassic rocks, have increased by a factor of 2–2.5.

The fourth area is located in the northwestern part of the Osinovskoye deposit and is characterized by exceptionally complex hydrogeological conditions. The Jurassic deposits in this area have a thickness of 30–40 m, are strongly weathered, cemented, and over a large area are overlain by highly water-saturated alluvial deposits of the low terraces of the Tom River. The water abundance of the Jurassic and Paleo-

…of Jurassic rocks is high; the specific yields of boreholes exceed 2–4 l/sec; the surface is swampy. This sector will be mined by the Kapitalnaya-III mine at the +100 horizon.

The materials presented show that the operating conditions of the deposit, in the presence of water-bearing Jurassic rocks in the roof, are complex. Water inflows and sudden breakthroughs into mine workings arise after the propagation of collapse and displacement of rocks into the Jurassic deposits and after their intersection with water-bearing zones and aquifer horizons. According to studies by special offices for fire extinguishing in the Prokopyevsk–Kiselevsk district of Kuzbass and by VNIMI (Avershin, 1954; Serednyakov, 1963), the zones of chaotic collapse above workings, on average, do not exceed three times the seam thickness, while the zone of intensive subsidence develops upward somewhat higher than the length of the longwall. Taking these provisions into account, as well as the general regularities in the water content of the Jurassic and Paleozoic rocks in the section, a forecast has been made of water inflows into mine workings and measures have been outlined for the safe conduct of mining operations beneath the Jurassic water-bearing rocks for each delineated sector.

In the first sector, to prevent increased water inflows, it is recommended to observe the ground surface, eliminate the effects of subsidence, isolate surface watercourses, and mine coal cautiously beneath the valleys of small rivers and water-bearing ravines.

In the second sector, groundwater of the Jurassic deposits will be drained by mine workings, providing stable inflows of water into the longwalls of up to 30–40 m³/h during the initial periods of mining and 10–20 m³/h subsequently (1.5–2.0 years). In the northern part, within the limits of the Kapitalnaya-III mine, inflows into the longwalls will increase to 50–60 m³/h. Upon encountering rupture disturbances and their capture by collapse zones, as well as with the development of subsidence zones up to aquifer horizons formed in relief depressions, sudden breakthroughs may occur, with inflows of up to 100–200 m³/h and more.

For the safe conduct of mining operations in this sector, it is necessary to drill advance boreholes into the contact zone in order to study the condition of the Jurassic and Paleozoic rocks and to determine the need for protective pillars to support the roof of ventilation crosscuts and longwalls and to drain waters from overlying horizons. The longwall mining layout must provide for drainage of groundwater into the mined-out and subsided part of the extraction area. The length of the longwalls should be selected with allowance for the development of the arch of intensive subsidence.

In the third sector, mining operations drain natural reserves of groundwater in the Jurassic deposits only within zones of disturbance and weakened rocks that are not supplied by constant recharge. These zones are limited in size and are difficult to identify during exploration work; therefore, they pose a great danger during mining operations. The total inflows of groundwater into the workings in this sector, within the prospective area of the Kapitalnaya-I mine, should not exceed 200–250 m³/h. In individual longwalls, during the initial period, they will amount to 20–50 m³/h; during the closure period, 5–15 m³/h.

For the safe conduct of extraction mining operations, it is necessary to drill advance boreholes in the near-contact zone, especially in areas of expected zones of rupture disturbances and depressions in the Paleozoic relief, for preliminary drainage of groundwater and for studying the condition of rocks in the contact zone in order to determine the factors of rock pressure. Provision is made for orienting the longwalls so as to direct water inflows into the caved part of the extraction area.

In all areas it is necessary to carry out systematic observations of water inflows into mine workings. At deep horizons it is recommended that the chemical composition of groundwater from the Jurassic deposits be studied simultaneously, with determination of the full range of microcomponents. The chemical composition of the waters and their temperature are direct criteria for assessing water inflows into mine workings. The chemical composition of groundwater in local watered zones that are weakly connected with the upper horizons is characterized by a sodium bicarbonate type, by the broad development of trace elements (copper, zinc, cobalt, molybdenum, etc.), increased mineralization (up to 1 g/l), and temperatures above 11–12°. Groundwater entering mine workings from the upper horizons has a calcium–sodium bicarbonate composition, contains a poor assemblage of trace elements, and its temperature is always below 7–8°C.

In the fourth area, given the presence in the roof of highly watered Jurassic rocks and alluvial deposits of the Tom River, and given the high waterlogging of the terrace surface, the conditions for coal mining will be exceptionally difficult. It is advisable to conduct mining operations in this area with complete stowing of the worked-out space, since the subsidence zone will always include the ground surface. Special hydrogeological investigations are required for a final resolution of the question.

LITERATURE

S. G. Avershin. Mine Workings beneath Structures and Bodies of Water. Ugletekhizdat, 1954.

G. M. Rogov, G. A. Plevako, L. A. Solomko. Hydrogeological conditions for the development of coal deposits in the Kuznetsk Basin. Proceedings of the 4th Conference on Groundwater of Siberia and the Far East. Irkutsk—Vladivostok, 1964.

P. Ya. Srednyakov. Pillar Systems for Mining Gently Dipping Coal Seams under Complex Mining-Geological Conditions. Gosgortekhizdat, 1963.