Лаборатория геологии техногенных процессов
Gorbunova K.A., Maximovich N.G., Kostarev V.P. Technogenic activation of karst sinks in Perm region // Proceeding 7 Int. Congress Ass. of Engineering Geology, V.3. Portugal, Lisboa, 1994.-P.1929-1931. /0,25/
TECHNOGENIC ACTIVATION OF KARST SINKS IN PERM REGION ACTIVATION TECHNOGENIQUE DE PHENOMENES KARSTIQUES DANS LA REGION DE PERM
K. A.Gorbunova, N.G. Maximovich,
ABSTRACT: The geological conditions of karst sink formation are shown. The main factors of karst activation and the manifestation of karst deformations of the ground surface under the effect of human activities are described
RESUME: On a etudie les conditions d'origine des fondrieres du karst. On characterise les facteurs principales d'activation du karst et les manifestations des deformations de la surface terrestre a cause du karst par l'influence de l'activite humaine.
1. OCCURANCE OF KARST
The technogenic activization of karst followed by formation of subsidences and sinks of the earth surface is examined in the process of design, construction and maintenance of engeneering structures in regions where soluble karstic rocks occur. In Perm region gypsum, anhydrites,salts, limestones, dolomites of the Paleozoic and. more rearly, carbonate rocks of the Proterozoic occur at low depth under the surface or stripped over an area of more than 30.000 square kilometers (Gorbunova et al. 1993).
The area contains three geological structures: the east margin of the East Europe Platform, the Pre-Urals Foredeep and the folded zone of the Urals. On the Platform mainly gypsum karst and, to a lesser degree,limestone and dolomite karst occurs; in the Foredeep salt and gypsum karst occurs, and in the folded zone of the Urals there occurs dolomite and limestone karst and, more rearly. marble karst. Karstic rocks are under eluvial and deluvial deposits, in river valleys they are under alluvial deposits or overlapped with non-karstic rocks of a relatively small thickness. More rearly they are stripped.
2. FACTORS OF KARST ACTTVIZATTON
The intensity of karst, one of the indicator of which is the frequency of sink formation depends both on natural and technogenic conditions and factors (Gorbunova et al., 1990). For example, salts in the Pre-Urals Foredeep occur at great depths. They are overlapped with non-karstic rocks. Under natural conditions the roof of a salt deposit in its arched uplifts is dissolved slowly and long. As a result of subsidence of the overlying deposits vast plane depressions are formed. Under the effect of mining in the Verkhnekamskoye Potash-magnesium Salt Deposit in 1986 a collapse sink formed which was 160 m deep and up to 100 m in diameter. One of the mines was flooded. Both slow sinking of the ground surface over karst cavities, areas of gypsum cover dissolution or in the places of suffosion influx in karsted rocks of loose sediments overlaying them, and sudden karst sinks are characteristic of the gypsum karst. The frequency of sink formation increases in zones affected by water reservoirs, highways, railway lines, oil and gas pipelines, mines and other engineering structures. The activization of karst during construction and maintenance of engineering structures is the result of their effect on the conditions and factors of karst formation. The following phenomena may be noted which affect the processes of dissolution, suffosion and soil caving.
1. Changes in the hydrogeological conditions (elevations of karst water level, the increase of karat water velocity and the amplitude of its level changes, formation of cones of depression) as a result of dam construction for water reservoirs, water pumping from mines, regular draining, intensive water intake.
2. Decrease of the thickness up to stripping of karstic rocks, of pverlaying sediments and changes in their composition and properties as a result of opencast mining of mineral resources and various types of construction activity.
3. Increase of natural water corrosiveness and water content in karsted areas in particular, due to leaks of industrial waste water and pumping of mine water.
4. Energence of centres of increased infiltration and inflow of natural water and industrial waste water due to relief changes as a result of construction works.
5. Changes in phisycal and mechanical properties of karstic rocks and sediments due to the increase in static and dynamic loads on the soil as a result of blasting, pile driving and transport traffic.
6. The increase in the permeability of rocks (emergence of pores, caverns, cracks and cavities in them) due to changes in hydrochemical and hydrodynamic conditions during deep mine or well sinking and operation. This is intensified by interflows between opened water-bearing horizons, injection of surface water into wells, pumping of mine water, treatment of wells with hydrochloric acid, internal stress relief in strata in the direction of mined-out spaces. In many cases the various adverse factors are in combination.
3. EXAMPLES OF SINKS
In 1954 a water storage was formed on the Kama river. In the area of its effect on karsted shores a sharp increase of the number of sinks was noted. On the territory of the town of Polazna 11 sinks were formed over the period of 1956-1961 whereas over the previous 50 years only 2 sinks had formed. The intensification of sinks formation process is explained by suffosive evacuation of loose fillers from cavities in gypsum under the conditions of higher levels of karst water and considerable amplitudes of their fluctuation. The main cause of the sink formation intensification in this case is the change of hydrodynamic conditions (factor 1). The gas pipelines from Siberia to the West through the central regions of Russia cross a zone of gypsum karst to the south of the city of Kungur. In the first years of pipeline laying the frequency of sink formation increased sharply. Along one of the pipeline sections 5.4 km long and 40 m wide 24 small sinks formed over the period from May. 1983 to September, 1984. The formation occured mostly in spring. In this case the main causes of sink formation activization were relief changes due to the levelling and disturbance of overlying deposits (factor 2 and 4). Over 20 sinks with the diameters up to 9 m have formed on the karsted territories of Perm region in the Pre-Ural area for over the period of the last 40 years. Over 200 sinks have been found along highways and their branches. The most of them are in road-side ditches and in soil reserves. The activization of sink formation has been caused by increased dynamic loads (factor 5) and other factors (2, 4). During driving of piles for foundations of living houses on construction sites in Kungur being aggregation terraces sinks having diameters of 4-8 meters formed. By static sounding and geophysical methods in the overlying loose soils around the sinks deconsolidated zones were found having diameters of 10-20 m (factor 5). An example of the effect of mining on the formation of sinks is the abovementioned sink in the district of Berezniki over one of salt mines (factor 6).
The karst danger of territories depend to a considerable degree on the frequency of sinks formation and the sizes of sinks. The classification of karsted territories based on the frequency of sink formation proposed by I.A.Savarensky was entered in standard technical documents. It has been supplemented with the assessment of stability categories by the sizes of karst sinks. In the districts of gypsum karst in Perm region there are karst areas belonging to category I, i.e. very instable (more than one sink formation per year) and to category II. i.e. unstable (from 0.1 to 1.0 sink formation per year. The sizes of new sinks are usually small, their diameters and depths do not exceed 3 m. To large sinks belong such as the sink near the town of Kishert formed in 1949 which is 50.5 x 40.0 m on the surface and which depth to the water is 9 m and that to the bottom is 14 m and that in the district of Berezniki formed in 1985 having a diameter of 100 m and a depth of 160 m.
The use of karsted territories is determined on the basis of comprehensive engineering and geological researches with due regard to their stability category which depends on the average diameter of karst sinks and the intensity of karst formation (the number of sinks formed per sq. km per year). These data allow to determine the necessity, the type and the scope of anti-karst protection of engineering structures under design. The most widely used types of anti-karst measures and the methods to assess their effectiveness are analysed in some publications (Tolmachev et al. 1986; Tolmachev, Reuter 1980).
The lack of reliable data on sinks in the poorly investigated district of Perm region makes it difficult to assess their stability on the basis of sink formation intensity and to choose the most effective anti-karst measures. The solution of these problems is possible through organization of karst monitoring, i.e. through establishing of a system of Karstosphere state assessment and prediction under the conditions of technogenic effects.
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Gorbunova, K.A., N.G. Maximovich, V.P.Kostarev, V.N. Andreitchuk 1990. Technogenic impact on the karst in Perm Region. Studia carsologica. 2: 37-42.
Tolmachev. V.V., F.Reuter 1990. Engineering karstology. Moscow.- Nedra Publishers (russ.)
Tolmachev, V.V., G.M. Troitsky, V.P.Khomenko 1986. Engineering and constructional exploitation of karsted territories. Moscow: Stroyizdat Publishers (russ.)