ON THE ISSUE OF MINING COAL FROM THE BELOVO DEPOSIT IN KUZBASS BENEATH THE VALLEY OF THE BACHAT RIVER

G. M. ROGOV

In the Belovo geological-economic district of Kuzbass there are six large coal deposits: Belovo, Bachat, Gramoteino, Krasnobrodsk, Novorossiisk, and Chertinsk—considerable areas of which lie beneath river valleys.

Because of the increased water abundance of the rocks beneath river valleys and the periodic flooding of low terraces, enormous reserves of hard coal are being left in conservation. Meanwhile, in Kuzbass attempts are increasingly being made to extract coal beneath alluvial deposits (Leninsk district—the valley of the Inya River; Kemerovo district—the valley of the Tom River, and others), and mining experience indicates the quite real possibility of carrying out mining operations beneath river valleys, in particular beneath the first terrace of the Bachat River in the field of the “Pionerka” mine of the Belovo deposit.

At present the “Pionerka” mine is developing the southeastern part of the deposit, situated on the watershed of the Inya and Bachat rivers, i.e., under favorable hydrogeological conditions. However, coal reserves in this area are limited, and therefore the question has arisen of mining the northwestern part of the deposit, which lies beneath the valley of the Bachat River (the so-called cut-in area).

Of greatest interest is seam 5 (average thickness 2.95 m), whose coals are suitable for coking without beneficiation, but whose reserves within the technical boundaries of 1941 have been almost worked out. The technical boundary of the 1941 reserve calculation for the mine field in the northwest passes along the pillar beneath the river valley (approximately along the elevation +189 m). As a result, reserves of 28,286 thousand tons remain beneath the river valley, including, for seam 5, \(A + B\)—4,119 thousand tons and \(C_1\)—2,177 thousand tons.

The cut-in area is located within the limits of the first terrace of the river. The surface of the terrace is flat, gently inclined to the north, and is dissected by a large number of shallow gullies of varying orientation (0.3–0.6 m deep). Surface elevations of the terrace within the area vary from 185.65 to 188.0 m.

The Bachat River, meandering, flows in a comparatively wide, deeply incised channel and has a number of abandoned oxbow lakes. The average values characterizing the river within the area are as follows: channel width 12–16 m, depth 0.5–3.0 m, current velocity 0.3–0.5 m/sec; maximum discharge during spring floods up to 100 m³/sec, average summer discharge 4.6 m³/sec, average winter discharge 0.58 m³/sec. The water level in the river during 1955–1957 fluctuated from 183.5 to 187.5 m. Maximal-

The maximum mark of the rise in the water level within the area was recorded in the spring of 1941 (over 58 years) and was 189.5 m.

The productive deposits developed over the area of the Belovo brachy-syncline are represented by fine-grained sandstones—43.5%, aleurolites—33.2%, argillites—20.4%, and coals—2.9%. The deposits of the Lenin Formation of the Kolchugino Series ($P_2$) form the core of the brachy-syncline and contain 14 coal seams of workable thickness. Weathering has extended to a considerable depth. Boreholes and mine workings have established that the thickness of strongly fractured rocks is 40–50 m, measured from the surface of the bedrock. With depth, open fracturing rapidly dies out and at depths on the order of 100–150 m is practically absent.

The Paleozoic rocks are covered by a continuous mantle of loose deposits. The thickness of this cover within the valley varies from 8.0 to 20.0 m.

The alluvial deposits in the upper part of the terrace section are represented by loess-like loams, which overlie layers of buried soils. Below are developed degraded loess-like loams and brown dense clays, lying on strongly clayey sands and gravels. The thickness of the deposits of the first terrace within the mining area is 7.0–13.0 m.

The first aquifer is confined to the gravels of the terrace and to sand lenses; owing to the persistence of the alluvial deposits it is developed everywhere in the river valley. The aquifer is confined, except for the area adjacent to the mine workings of the “Pionerka” mine, where the groundwater is drained (Fig. 1). The head of the aquifer varies from 4.5 to 17.0 m. The water yield of the gravels has been tested by pumping and by filling tests. The values of specific discharge vary from 0.03 to 0.5 l/sec, most often not exceeding 0.15 l/sec.

Fig. 1. Map of the mining area of the Belovo deposit.
1. Boreholes. 2. Boundary of maximum flooding of the first terrace (1941, to elev. 189.5 m). 3. Outline of drained gravels. 4. Groundwater level. 5. Principal directions of groundwater movement. 6. Outlines of the city of Belovo.

The filtration coefficient of the terrace pebble beds varies from 1.5 to 23.4 m/day, with an average value of 9.0 m/day.

The water abundance of the Paleozoic rocks is not everywhere the same. Within the bedrock slope the rocks are weakly water-bearing; specific yields vary from 0.01 to 0.5 l/sec, whereas in the river valley they amount to 0.5–5.9 l/sec. The aquifer is associated with the weathered, fractured part of the bedrock. The rocks are most water-bearing to a depth of 60–70 m. Here the value of the specific yield does not fall below 0.5 l/sec.

In the river valley, increased water abundance is characteristic not only of the sandstones in the roof of seam 5, but also of the rocks enclosing seams 8–13, occurring to a depth of 60–70 m. The filtration coefficient of the rocks varies from 5.5 to 17.3 m/day, with an average value of 6.0 m/day. Rocks occurring at depths greater than 70 m are only slightly watered. The specific yield is only 0.1–0.4 l/sec, and the filtration coefficient is 0.2–2.0 m/day.

The water abundance of rocks at depths of more than 100–150 m has been tested by boreholes. The specific water absorption is determined as 0.001–0.008 l/sec.

The increased water saturation of the rocks in the river valley is due, first, to the fact that the valley is a natural drain for underground waters, where, in the strongly fractured zone of the productive deposits, there is an underground flow possessing large static reserves; second, there are favorable conditions for replenishment of the reserves from ground and surface waters. On watershed areas, underground waters occur at great depth, in a zone of weakly fractured rocks; therefore their recharge is impeded and the reserves are limited.

Long-term observations of water inflow into mine workings (see table) show that its distribution by mine

Table

is extremely uneven. The main mass of water enters workings that have opened seam 5. The most waterlogged workings are in the northwestern part of the mine field, driven beneath alluvial deposits (Bremсberg No. 4). The same was observed in 1936–1937 during the extraction of seams 9 and 10 in the northwestern part of the field, near the river valley.

The inflow of water into the workings of the southern part of the mine field is considerably smaller, although the extent of the workings is several times greater than that of the northern ones. The increased inflows of water into the northern workings are due to the entry of water from water-saturated rocks lying beneath the river valley. Thus, the total inflow into mine 205 m³/hr, recorded in August 1955, consists of an inflow into the northern workings of 145 m³/hr (including 139 m³/hr in Bremсberg No. 4) and into the southern workings of 60 m³/hr. In September 1957, the inflow into the northern workings was 105 m³/hr (95 m³/hr in Bremсberg No. 4), and into the southern workings 40 m³/hr. These data show that almost 3/4 of the total water inflow into the mine enters the northern workings, namely Bremсberg 4.

The character of the entry of water into development and extraction workings differs. When the face of the main drift advances, the inflow is usually concentrated at the face; water enters in the form of intensified dripping or small streams from cracks and disturbed zones. A significant inflow into extraction workings occurs after the mined-out space caves.

As analysis of the factual material shows, the increase in average annual inflows (to 303 m³/hr in 1948) occurred as the mine workings approached the river valley. After work was discontinued in 1949–1952 in longwalls Nos. 58, 59, 68, 69, 69 bis, and 78, adjoining the first terrace of the Bachat River (Fig. 1), the inflows began to decrease sharply. The decline in inflows is due to the drainage of static reserves in the zone of the mine’s depression cone. Regime observations have shown that at present the depression cone continues to grow (the water level in borehole 314 fell by 1.04 m over 9 months).

Analyzing the hydrogeological conditions of the mine-field cut-out area, it should be noted that the water saturation of the bedrock and gravels does not pose a substantial threat to mining operations beneath the river valley. The complicating factors are the periodic flooding of the first terrace by river waters during spring freshets and the shallow occurrence of seam 5 from the surface, since in the axial part of the syncline the seam lies at a depth of 40–50 m, while on the limbs it comes out directly beneath the gravels.

Under such conditions, the cracks and collapse funnels that will undoubtedly appear after caving of the roof will constitute good pathways for the penetration of surface waters into the mine workings. Thus, extraction of seam 5 with caving of the roof cannot be carried out without first protecting the cut-out area against floodwaters. In addition, the system of mining with roof caving will be made difficult by the fact that the southeastern part of the town of Belovo is located on the area being undermined.

All of the above, as well as the increase in the cost per ton of mined coal by 4.93 rubles owing to the costs of carrying out protective measures in the cut-out area, calls into question the rationality of the seam 5 mining option proposed by the Belovougol Trust. Moreover, despite the enormous volume of earthworks and high operating costs, this option for extracting seam 5 does not completely eliminate the possibility of a breakthrough of surface waters into the workings.

In addition, when coal is extracted according to this variant, after mining operations on the site have ended and water drainage from the mine has ceased, the river valley (the eastern outskirts of the city of Belovo) will become swampy as a result of the restoration of the original groundwater level. If, before the exploitation of the Belovo deposit, the low-water groundwater level in the river valley lay at a depth of 2.5–3.5 m, then after subsidence of the roof of seam 5 and subsidence of the surface of the first terrace by 2.0–2.3 m, the groundwater level will lie at a depth of 0.5–1.5 m.

Special hydrogeological investigations carried out with the author’s participation in 1955–1956 on the cut-in section and in the mine workings adjoining the river valley made it possible to propose another variant. Under this variant it is proposed that seam 5 be mined with stowing of the worked-out space, without carrying out any work on the surface of the first terrace or in the channel of the Bachat River. With this variant of mining the seam, the possibility of surface waters breaking into the mine workings is completely eliminated. With good organization of the work, this variant may prove more profitable. When the coal is mined with stowing of the worked-out space, the southeastern outskirts of the city of Belovo will be preserved and will remain suitable for further construction on an area of 1.5 sq. km east of the city.

The smooth and uniform subsidence of the rocks in the roof of seam 5 by 0.1–0.25 m, when coal is mined with stowing of the worked-out space, will have no effect whatever on the character of the terrace surface or on the existing light-type structures.

The inflow into the mine workings has been calculated for the case of mining seam 5, which occurs in the most water-bearing rocks. Water inflows into the workings when other seams, lying at greater depth, are mined will be considerably smaller. The maximum water inflows into the mine workings will be observed during periods of spring floods. At this time the inflow consists of underground, groundwater, and surface waters entering the mine workings. Underground and groundwater enter the workings from the productive deposits and the pebbles of the first terrace. Surface waters will enter by infiltration from the river channel and, in part (when the terrace surface is flooded), through the loamy terrace deposits.

For a preliminary calculation of the expected water inflows into the mine workings, the following parameters were adopted: the thickness of the water-bearing horizon was taken as the upper, most fissured zone of the productive deposits ($H = 35.0$ m); the filtration coefficient, 6 m/day; the filtration regime, laminar. The expected inflows were calculated for the mining of seam 5 according to the second variant.

The total water inflow into the mine workings of the Pionerka mine, with the development of mining operations in seam 5, will be 600–650 m³/hour, including an inflow of underground and groundwater of 540–560 m³/hour, infiltration from the river channel of 20–30 m³/hour, and infiltration through the deposits of the first terrace (during periods when the latter is flooded) of 40–60 m³/hour.

Analyzing the hydrogeological conditions of the site and bearing in mind the minimal time required to prepare it for exploitation, extraction work for seam 5 should be begun from the pillar beneath the channel of the Bachat River toward the former mine workings, in a retreating direction (see Fig. 1). Under such a scheme for opening up the site, the cut-in section will be divided into two parts: (a) the section up to the pillar beneath the channel of the Bachat River and (b) the section beyond the pillar. After the main drift is driven along the axis of the syncline (the continuation of bremberg 4) and district brembergs are cut to both sides as far as the outcrops of the seam beneath the alluvium, a draining barrier will be created, which will make it possible to receive maximum inflows (600–650 m³/hour) of underground waters along the contour of the out—

of the dissected area. With such a mine-opening scheme, stoping operations will be carried out under favorable hydrogeological conditions, with insignificant inflows of water into the faces of the stoping workings.

The preparation and cutting of the second area (behind the barrier pillar under the river channel) can be carried out in parallel with stoping operations in the first area. This area can be worked in a forward direction, with the mining operations advancing from the river channel toward the northwestern closure of the fold. Water inflows in the second area will reach their maximum value in the initial period of development of the mining operations, and as the workings move away from the river they will decrease. By the time mining operations in seam 5 are completed, the inflows will not exceed 350–400 m³/hr, since the development of underground mine workings will cause drainage of the static reserves of groundwater in the river valley. As for replenishment of groundwater reserves from the left-bank part of the river valley, it will be insignificant owing to the weak water abundance of the rocks.

The driving of mine workings in the river valley will considerably accelerate the development of the mine’s depression cone. With full development of mining operations in seam 5, the drainage zone will include the entire eastern outskirts of the city of Belovo, including the territory of the railway junction and the zinc plant. It should be noted that, in this case, the yields of the water-supply wells of a number of the city’s enterprises on this territory will decrease considerably, and the wells used by residents will become dry. The drainage zone will also include the water intake (of 5 wells) of the Belovo station railway junction, which supplies potable and technical water to the depot, the foundry, and the adjacent part of the city.

During the development of seam 5, this water intake will reduce its yield, and after mining operations have been carried out in seams 8, 9, 10, 11, 13, 16, and 17, it will find itself in a zone of drained rocks. In connection with coal extraction beneath the valley of the Bachat River, the question of the water supply of the city of Belovo will become still more acute.

Thus, taking into account what has been set forth above, the following conclusions may be drawn:

1. The total maximum water inflow during the development of mining operations in seam 5 will not exceed 650 m³/hr.

2. It is apparently more rational to mine seam 5 beneath the river valley with stowing of the worked-out space. Under such a mining system, the possibility of flooding the mine workings with surface waters will be eliminated, there will be no need to demolish the eastern outskirts of the city of Belovo, and an area of 150 ha will remain suitable for construction. For the final selection of the variant for mining seam 5, it is necessary to carry out economic calculations.

3. In connection with coal extraction beneath the river valley, it is necessary urgently to resolve the water-supply problems of the city of Belovo.

Tomsk Polytechnic Institute
named after S. M. Kirov