The Leningrad oil shale deposit is located in the west of the Leningrad Region and is the eastern part of the Baltic oil shale basin. The industrial oil shale bed (promplast) lies in the lower part of the Kuker stratigraphic horizon of the Middle Ordovician and consists of four convergent layers of oil shale, separated by interlayers of limestone ...

When designing and implementing the dewatering of mineral deposits it is necessary to take into account and use the experience of already conducted dewatering on similar or close to them deposits. One of such objects, interesting in hydrogeological respect, for which the known experience of dewatering has already been accumulated, is Safonovskoye deposit of brown coal and refractory clays in Smolensk region. Exploration and study of its hydrogeological conditions began in the post-war years and continued until 1950. Some additional works were carried out later - up to 1962. On the basis of exploration works more than 8 mines were designed. The construction of the first mines started in 1949. The mines were successively put into operation: 1 - in 1953, 2 - in 1954, 3 and 4 - in 1956, 8 - in 1957, 6 - in 1958, 7 - in 1959. At the end of 1959 the construction of mine 5 was completed, which is currently intended only for the extraction of refractory clay.

Drilling wells are widely used for pumping water from water-abundant rocks in urban, industrial, transportation and agricultural water supply, drainage of mines and quarries, water control during construction of large hydraulic structures, etc. Under appropriate hydrogeological conditions, such wells are often equipped with high-performance pumps, as a result of which a significant depression funnel is formed around the well in the aquifer. Filtration rates and hydraulic gradients near the water-receiving part of the well, especially with a pressurized aquifer, may exceed the values obeying the linear law of filtration. Then in the zone nearest to the well there is most often a turbulent type of movement, characterized, as is known, by a quadratic relationship between the velocity of groundwater and hydraulic gradient. It occurs more often in fractured rocks, but can also occur in coarse clastic and granular material.

In hydraulic engineering construction, mining, construction of subways, construction of deep foundations, etc., the method of artificial lowering of groundwater level is used more and more often. Especially widespread has found water lowering on modern grandiose hydraulic engineering construction sites, such as the Volga-Don, Kakhov hydroelectric complex, construction of hydroelectric stations near Kuibyshev and Stalingrad and others. There are also known a number of cases of sinking mine shafts and dewatering of coal and other mineral deposits with the help of dewatering plants. At the same time, when designing new dewatering installations or rearrangement of existing drainage systems consisting of variously designed dewatering wells, drainage wells, needle filters, etc., there are difficulties in calculations of the main efficiency indicators of such installations. They mean calculations of necessary level lowering in any point of the site, determination of total water inflow at different location and different design of drainage devices, determination of flow rate of separate interacting excavations, etc. For these calculations, in turn, it is necessary to have such indicators as water permeability coefficient, radius of influence and some others.

Widespread use of the method of artificial lowering of the groundwater level in the construction of foundations for hydraulic and industrial structures, as well as large high-rise buildings caused the need to develop a methodology for calculating the water inflow to excavations in different hydrogeological conditions. The present article deals with the case of water inflow to the dewatering unit of an excavation, elongated in plan form, under the conditions of pressure-unpressurized regime of aquifers opened by the excavation. Attention to this case was attracted by the construction of a lock on a navigable canal. In spite of its special character, the set task is also of theoretical interest, as it allows us to check the suitability of certain calculation schemes and formulas in specific hydrogeological conditions. The excavation of the mentioned structure has already been realized at present, and the forecast of possible groundwater level lowering, which was given in 1952 when designing the structure on the basis of the calculations given below, was mostly confirmed.