Лаборатория геологии техногенных процессов
Gorbunova K.A., Maximovich N.G., Kostarev V.P., Andreichuk V.N. Technogenic impact on the Karst in Perm region // Geology, Climate, Hydrology and Karst Formation: Project IGCP 299, Newsletter. - Guilin, China, 1991.- P.85-90. /0,6/
TECHNOGENIC IMPACT ON THE KARST IN PERM REGION
K. A. Gorbunova, N. G. Maximovich, V. P. Kostarev, V. N. Andreichuk
GEOLOGICAL BACKGROUND
The Perm Region territory of 1606 sq.km is situated within three large geotectonic units: the eastern margin of the eastern European platform,pre-Urals foredeep and the folded belt of the Urals zone. The Paleozoic karstified rocks:limestones,dolomites,gypsums,anhydrites,salts are exposed or occur not deep from the surface on the area of about 30 thousands sq.km. Numberous boreholes in the carbonate rocks have revealed paleo-karst.
The karstified rocks occur in the form of anticline and syncline folds accompanied with fracture dislocations. Typical are sinkholes, solutional basins, lost rivers, springs, caves and blind creeks.
TYPES OF TECHNOGENIC EFFECTS ON THE ECOLOGICAL MEDIUM OF KARST AREAS
Perm region bears a considerable technogenic load. The distribution of various types of technogenic effects on the environment is conditioned by the presence of commercial mineral deposits,timber and water resources , the geographic position of the region on the border of the western and eastern areas of USSR,the history of its development. The greatest changes of the geological medium of the karst areas are caused as a result of various types of the human economic activities, such as: 1) mining industry (Kizel Coal Basin,Verkhnekamskoye Potash Salts Deposit,Volgo-Urals Oil and Gas Bearing Area); 2) hydrotechnical construction (Kamskaya hydroelectric station and Kamskoye reservoir); 3) urban and industrial construction (on the basis of commercial mineral deposits,timber and water resources in Perm Region there appeared large industrial centers--cities of Perm, Berezniki, Kizel, Chusovoy and others); 4) communication and transport constructions (the region is crossed by railway and highway lines, electric transmission lines,oil and gas pipelines); 5) water distribution systems (use of fresh drinking,medicinal and commercial mineral water); 6) timber industry and agricultural activities (tree felling,chemical effect from agriculture).
All these kinds of the human economic activies change some components of the environment (overburdon and karstified rocks,relief,underground and surface waters, atmosphere, biosphere) which is reflected directly or indirectly on the basic conditions for karst develoment and causes its activition or declining.
TECHNOGENIC CHANGES OF KARSTIFIED ROCKS AND OVERLAYING DEPOSITS
In many construction types,mining,guarrying (especially gypsum and limestone) the soil cover blanket deposits are removed partially or entirely,the karstified rocks are exposed. In some cases,the removed soils are used in construction forming media aggressive to karstified rocks. In other cases, the solid waste disposal consist of soluble minerals. The constructions being erected and their operation create static (industrial and civil objects,reservoirs) and dynamic loads (blasthole drilling,intensive transport traffic).
The consequence of these types of economic activity is change of the stressed condition of karstified rocks, their fracturing, formation of technogenic landscape, appearence of concentrated absorption centers of atmospheric precipitation and karst waters rechange.
The activation of karst caused by the disturbance of the cover and redistribution of the surface run-off was observed in the area of the main gas pipelines Siberia-Center-West. They cross the western limb of the Ufa swell to the south of the city of Kungur where are karstified gypsums and anhydrites, to a less degree the limestones and dolomites of the Kungurian stage. There can be traced a connection of the karst and the river network with tectonic dislocations. Most karstified area are the sites where the gypsums are exposed or covered with soil vegetation layer or eluvium of small thickness.The number of sinkholes for 1 ha here reaches 95, the area of sinkholes totals 50 per cent of the site area. The initial size of the collapse sinks is 2 to 3 m,the average diameter of the sinkholes is 7 to 8 m.From May 1983 to October 1984 in the gas pipeline area of 40 m wide and 5.4 km long there appeared 24 collapse sinkholes, and in 1985 their number exceeded 45. A great part of the collapse sinks had diameter of no more than 2.5 m,depth of 2 m and only in some cases 5 m.
At present, such collapse presented no danger, but further activation of collapse may have negative sequences. To provide safety of construction and gas pipelines, antikarst measures were recommended: filling the karst sinks with non-draining material, arranging of the surface waters run-off, reduction of transport load,stop of blasting operations in the pipeline area.The condition of the constructions is being monitored.
Intensity of the collapse process increase after construction of industrial and civil objects and roads,the collapse sizes being increased. For example, from 1960 to 1971 in Kungur region in road-side ditches and reserves there appeared 22 collapse.
In quarring of limestones and gypsum the overlaying deposits are removed. Blasting operations in quarries lead to fracture forming and opening in the rocks which promotes infiltration of atmospheric precipitation.The suffosion and dissolution activation causes numerous suffosion-karstic collapses, for example, in the vicinity of the gypsum quarry Yergach to the north-west of Kungur.
TECHNOGENIC EFFECTS ON UNDERGROUND WATERS OF KARSTIFIED MASSIFS
The karst activation is caused by variation regime of the level and chemical composition of the karstic waters in the water intake areas,in mine and quarry outfall and drainage system.In these cases, the hydrodynamic zones are shifted,the karstic water flow direction changes and the velocity increases.
In Kizel Coal Basin the coal-bearing strata of the Visean stage of the Lower Carboniferous series occurs under the karstified carbonate rocks. Some mines passed through cavities and caves filled with water. In the karst influence zone,the mine water inflow reach 2000 to 2500 m"?/h. As a result of the karst waters drainage thick strata of carbonate rocks are involved in the active water exchange and karstification. In interaction with sulfur-containing coal-bearing rocks,the bicarbonate karst waters are transformed into bisulphate waters enriched with ferrum,aluminium and other microcomponents. The mine waters run down into rivers and are partially absorbed by ponors. Moving along karst channels in carbonate rocks the bisulphate (PH 3 to 4) polluted mine waters are partially neutralized and cleaned. In the southern part of the basin the mine waters are released into the river Gluhkaya which disappears in the cave and flows for 7 km by underground route. The river feeds a spring in the valley of the river Chusovaya whose freshet discharge reaches 10 thousand m"?/h. After the mine waters passing through the underground karst channels the ferrum, aluminium and sulphate concentration reduces ten and hundreds of time. At the same time there occurs contamination of stalactites and stalagmites in caves with ferrum hydroxides. Some cavities are filled by sediments.
The recharge,circulation and outflow conditions and the chemical composition of karst waters change considerably in the influence zones of hydroelectric stations and reservoirs. Near Perm, on the river Kama, the Kamskaya Hydro was constructed in 1954. On the dam foundation, under argillites, sandstones, gypsum limestones and dolomites of the Ufimian stage, there occur gypsums and anhydrites of the Kungurian stage which are regional waterproofs. After filling the reservoir filtration was intensified at the dam foundation. In some parts sulphate waters appears which indicates the dissolution of gypsum. In this situation, consolidation of the existing cement curtain was done with a chemical gelforming silicate solution. The injection consolidation and post-injection processes provided gypsum protection against dissolution and increased the stability of the dam.
Filling the Kamskoye reservoir raised the water level by 20 to 22m. Its banks within the limits of the Krasnokamsk-Polazna swell are laid with gypsums and anhydrite of the Kungurian stage. Part of the caves was inundated. In the waves impact zone there formed leaching processes and new small caves. Introduction of the river waters into the karstified rocks, seasonal fluctuations of the water level in the shore area reaching 7 to 8 m, caused activation of suffosion, removal of material from the filled karst cavities, gypsum dissolution and collapse forming. In the reservoir influence zone on the territory of the settlement Polazna, from 1956 to 1961 there occured 11 collapses while for the previous 50 years there were only two.
The karst activation both in the upper and deep horizons is observed in connection with drilling operations for oil, gas and salt as well as development of oil and potash salts deposits in the same areas. The boreholes are imperfect which cause vertical flow exchange and mixing of mineralized and fresh waters and increase the waters aggressivity towards the soluble rock. Some abandoned wells gush polluting the rivers. At present well constructions are improved to provide the aquifer isolation.
About 50 per cent of oil resources is confined to fractural karst reservoirs. Developing a greater part of a deposits by fresh water injection into wells to maintain pressure can activate the dissolution processes of carbonate and sulphate salts in deep horizons. The processes are promoted by activity of sulphate-reducing bacteria. To intensify the oil inflow, the hydrochloric acid is injected into the seam (up to 100 m3 and more) at the concentration of 10 to 20%. As a result of the carbonate rocks dissolution near the well, the volume of the fractural karst reservoirs and the oil inflows increase. As noted by I.N.Shestov et al, an active impact on karstified rocks in the oil development wells spreads over to the depth of hundreds of meters.
COMPLEX CHARACTER OF TECHNOGENIC IMPACT ON THE ENVIRONMENT IN KARST AREAS
In territories of considerable technogenic load, the conditions and factors of karst formation change considerably due to irreversible transformations of the landscape and the rocks, pollution of surface and underground waters, atmosphere and atmospheric precipitation, degradation of vegetation.
An example is Verchnekamsky industrial complex including, besides potash salts enterprises of the city, settlements, large water intakes, linear (engineering) constructions, timber processing and oil industries. The salt extraction has been taking place there for more than 500 years. The salt stratum of the Kungurian stage (underlying rock salt, potash salt, overlying rock salt) and the intermediate stratum are overlied with clays, limestones, gypsums, marls,sandstones of the Ufimian stage and Quaternary deposits to which aquifers are confined. In chamber working of potash salts artificial cavities are formed, redistribution of stresses in the rocks takes place, opening of fractures in the overlying rocks, slow sinking of the surface. According to G.V.Beltyukov, in driving and developing all the mine shafts in fractural zones there are noted waters shows. In the overlying rock salt and in the carnallite rock in some places there were uncovered karst cavities of hundreds of cubic meters in volume. In July 1986 in one of the sites there occured a collapse sink. It had the size of 40 by 80 m on the plane with the depth of 25 m to the water level. The collapse was accompanied by a gas explosion and light effect.
In worked-out tunnels there condenses moisture in the form of small pools or drip from the roof. In some sites it dissolves the salt, in others there deposistalactites and sinter salt crusts from oversaturated brines. The salt leaching zones formation had been promoted by, in the past, brine extraction from more than 200 wells of salt industry. Some abandoned wells have turned into "artificial" springs. In drilling wells of the former salt fields karst cavities were uncovered in the salt strata.
The potash salt industry occupy an area of more than 700 ha. Every year they increase by several millions of tons. The mine dump and industrial liquid wast receivers pollute the environment by salinization and create a lifeless technogenic landscape. In salt mine dump there develops a peculiar "technogenic" karst under the effect of atmospheric precipitation and temporary surface run-off: numerous ponors, karren, small sinkholes, channels and caves.
CONCLUSION
Various kinds of the human economic activities called technogenic impact change karstic processes course. These changes have various trends. In most cases the technogenic impact lead to activation of karst processes as a result of the environment change (rocks, hydrosphere, atmosphere, biosphere) which determine the basic conditions and factors of karst formation. The karst activation has a negative impact on engineering geological conditions and may cause hazardous situations. It shows itself not only in upper but in much deeper horizons of the rocks. Slowing of the karst process is a result of some or other engineering geological measures connected with construction on karstified rocks. The environmental response to the technogenic impact depends on the karst type: saline, sulphate, carbonate. As a result of mining activities on the surface there accumulate soluble technogenic soils which show "technogenic karst". Remove of dissolved components from the soils pollute the environment. The human economic activities being planned in karst areas must be based on the predictions of the karst process in view of the environmental changes under the influence of the existing and designing engineering works and providing nature protection measures.
|
|
|
