In order to understand the earth pressure phenomena it is very important to investigate the distribution of stress and deformation around underground openings. Process of deformations, in general, is influenced by different mechanical properties of rock surroundings of the underground openings. Process of deformation Changes the stress conditions in rock massif. In this work, we want to analyze the experimental results of deformation velocity distribution around underground Openings of circular cross section. A series of in situ test data were used to estimate the deformation velocity and stress distribution in rock salt mass as a visco:elasto:plastic rock.

The distribution od deformation velocity, presented with isotache linies, in different massif depths around circular openings are presented in the three different time periods; from 0 to 60 days,60 to 180 days and for 180 to 1000 days.

An initial stage of stress around circular opening in a rock salt is also presented. some other results of investigations in the Tušanj rock salt mine, which are of interest in this cause, are presented in this paper, as well.

Underground openings in competent rock, in general, sustain the elastic deformations on the frame in the moment of underground excavation. The further deformations on the opening frame and dip in massif, depend on rheological properties of surrounding rocks and on the state of strees around the openings. It is possible to predict by the laboratory investigation the elasto-plasic-viscous behaviour of rock if the stresses around the opening does not upset the 70 to 80%< of the rock strength.

After a centain period of time, because of the rheological deformations of masif, the redistribution of stresses around the underground openings occurs, until the equilibrium state of the stress is not restituted. In the begining of the underground opening exising, radial stress from the zero values on the frame rise diper in masif, fig. 1. Tangential stress decrease from the maximum values on the frame, until both stresses become one value, H, see, fig. 1.a. The state of stress at any point of the massif depend on the ratio of undeground opening diametar, Ro, and the distance to the examined point, R. As the difference in state of stress in different points in masif occurs, radial deformations of different elementar volume of massif have different values. In general, time displacements of rock massif around unsupported underground opening in competent rock has direction to the central axis of the opening, fig. 1.g.

In this work we want to present the migration of the area of deformation around the underground openings during a very long period of time.

(Figure in full paper)

Obtained results for Tušanj rock salt are presented in figure 2. Constant m becomes negative and is dependent on scale effect height to width ratio} on the samples. For height to width ratio, h:b=1, m=-14.6; h:b=Z, m=-8.6; h:b=3, m=-7.9; h:b=4,m=-7.9. It can be seen in the fig. 2 that strength of rock salt become greater as greater sample volume is, with constant scale effect (height to width ratio of the samples)

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