Wodochłonność skał fliszowych w wybranych rejonach Karpat

Henryk Niedzielski


Water pressure tests of flysch rocks in selected areas of the Carpathians

The present paper deals with water capacity tests in sandstones and shales of the Polish flysch Carpathians. The tests were carried out in eight areas marked in Fig. 1. The geological and tectonic conditions of the areas under investigation are illustrated in figures 2—7. The “water capacity” is, according to the author, the amount of water pumped into 3—5 im boring section (zone) under the pressure of 2 atmospheres, measured in litres per minute per 1 metre of section length and per 0,1 atmosphere. The results of water capacity tests obtained in respective regions are presented in Tables 1—9. There has been searched a connection of water capacity with lithology, tectonic conditions and the depth within the range up to 100 metres below the land surface. The above dependences were analysed separately on slopes of valleys and on their floors. Water capacity tests carried out in 840 zones lead the author to the following conclusions. The greatest water capacity occurs at a depth of 15 metres from the land surface (up to about 9—10 metres below the Quaternary cover). It results from a thick network of rock formation fissuring, caused by weathering processes. At greater depths the weathering processes rather do not influence the thickness of rock fissuring. The thick network of fissuring and great water capacity connected with it may reach up to 30 metres in depth in case deep rock slides occur there. It has been shown in many cases that the quantity of water capacity is closely connected with tectonics, below a depth of 15 metres and rarely 30 metres. The water capacity is great near dislocation and it diminishes while carrying away from the latter. As a result of it, there is no close correlation between water capacity and depth. However, the extremely greatest values of water capacity decrease while the depth increases; it happens both on valley floors and on their slopes (see Fig. 8). The figure shows that in four regions the water capacity value diminishes very slowly with the depth, and only in the interval between 75 and 95 metres in depth it rapidly falls and reaches the value of 0,05 l/min • m • 0,1 atm. This value corresponds to the criterion of watertightness of rocks, assumed in the present work. In the four remaining regions on slopes of valleys the value of water capacity decreases faster with the depth and it reaches the criterion of watertightness between 45 and 65 metres in depth. On the floor of valleys the extremely greatest values of water capacity gradually reach the criterion of watertightness in a wide interval from 25 to 75 metres in depth 'below the territory surface. The author presents the opinion that water capacity smaller than 0,05 l/mm • m • 0,l atm. is characteristic of practically impervious rocks. The calculation of boundary below which water capacity is smaller than 0,05 1/min • m • 0,01 atm. allows a determination of parameters for watertight screens in hydrotechnic constructions, as well as of the optimum depth of a drinking water well. The optimum depth of a well in the Carpathians should amount from 30 to 60 metres on the floor of valleys and from 45 to 80 metres on their walls. It has been found out in some regions that water capacity is alike in “subfacies” of sandy and shaly flysch, occurring in similar tectonic conditions.

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