Abstract
With the rapid development of tunnel construction in China, deep buried and long tunnel projects are emerging in areas with complex engineering geological conditions and harsh environment, and thus large deformation of tunnels under conditions of high in situ stress and soft rock becomes increasingly prominent and endangers engineering safety. Therefore, it is of great significance to control the deformation and improve the stability of surrounding rock by analyzing the thickness and distribution law of loose circle according to the unique mechanical properties and failure mechanism of surrounding rock of large deformation soft-rock tunnel. Based on unified strength theory, this paper deduces the radius calculation formula of the loose circle by considering the influence of intermediate principal stress. Furthermore, the theoretical calculations and field tests of the loose circle in the typical sections of grade II and III deformation of Yuntunbao tunnel are carried out, and the thickness and distribution law of loose circle of surrounding rock of large deformation soft-rock tunnel is revealed. The results show that the formula based on the unified strength criterion is applicable for a large deformation tunnel in soft rock.
Highlights
With the development of transportation facilities in western mountainous areas of China, more and more tunnels are built in soft rock areas with high in situ stress
Based on unified strength criterion, in this paper, there is the deduction of the formula for calculating the radius of the loose circle of surrounding rock in the tunnel, theoretical calculation, and field test of surrounding rock loose circle for typical sections of grade II and III soft rock with large deformation which is carried out in Yuntunbao Tunnel and analyzes the distribution range and law of loose circle of surrounding rock in large deformation tunnel of soft rock
E main conclusions are as follows: (1) Based on the objective fact that high in situ stress exists in large deformation tunnel in soft rock, a formula for calculating the radius of the loose circle is derived with unified strength criterion and considering the influence of intermediate principal stress on the stress state of surrounding rock
Summary
With the development of transportation facilities in western mountainous areas of China, more and more tunnels are built in soft rock areas with high in situ stress. Because the stress redistribution after tunnel excavation will form a ring-shaped fracture zone within a certain range in its section space, that is, the loose circle of surrounding rock [15], of which the distribution range and law have a great influence on the stability of surrounding rock [16,17,18,19]. It is of great significance to study systematically the thickness and distribution law of loose circle of surrounding rock of large deformation soft-rock tunnel for controlling the deformation and improving the stability of surrounding rock. Based on the systematic classification of large deformations, the thickness formula of the loose circle in surrounding rock of large deformation soft-rock tunnel is derived based on unified strength criterion, and the thickness and distribution law of loose circle of Yuntunbao tunnel is analyzed with field acoustic wave test
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