Rock failure mechanisms in the surrounding rock masses with deep level tunnels and in the source areas of disastrous events
Baranov V.A.
VLADIMIR A. BARANOV, Doctor of Geological Sciences, Head, a Laboratory of the Institute of Geotechnical Mechanics, Dnepropetrovsk, Ukraine. St. Simferopol, 2a, Dnepropetrovsk, Ukraine, 49005, E-mail: baranov-va@rambler.ru
Anisotropy zones of the stressed rock massifs
In the last decades, the depth of mountain works has considerably increased (up to two, three and even four km) and the depth of mine hole drilling has attained ten and more km. The mountain pressure changes with every step as the mountain works deepen: together with the fall and displacement of rocks, more frequently occur bouncing, shelling, mountain blows, sudden outbursts, pillar crushes, squeezing out of the structural elements of the working, etc. The stressed state in mountain rocks has three basic variants: the predominating vertical stress; the predominating horizontal stress, and about the same horizontal and vertical stresses. The principal causes and conditions for anomalous horizontal and vertical stresses have been considered in this paper.
The opinion that the stresses in rock massifs are caused by gravitation and horizontal stress may be right only in specific cases. In actual practice, the stressed state is caused not only by gravitational forces but tectonic processes as well involving local concentration of stresses or relief. It may be caused also by temperature changes and chemical variations conditioned by the history of rock formation and stressing as well as rock weathering. The relaxations of stresses, the presumable widening of the sea bottom, the drift of continents caused by convectional processes and other factors play their part in it, too.
In general, one can recognise that the solidity and the stressed state of rocks increase with increasing depth. However, the results of researches testify that, in some places, at a depth of several hundred metres, the horizontal stresses exceed significantly the lithostatic loads, so the pressure may hardly be attributed to the weight of the over-laid rocks. Real measurements of the stressed state taken in the mountain rocks of various types at a depth of several thousand metres brought out significant changes in horizontal stresses varying between 0 and 150–200 MPa. Notable are the facts that the excessive stresses are connected with the crystalline rocks of the foundation, whereas considerable horizontal stresses are not characteristic of sedimentary rocks and hypergenesis areas.
Key words: anisotropy zones, stresses, rock massifs.
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