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Measurement of natural tectonic state of stress in rock foundation by back calculation method with deformation of tunnel contour

The state of stress of rock foundation is defined by gravitational and tectonic force fields. The gravitational force field can not be separated from the rock materials. | T~p Journal of Mechanics, NCNST of Vietnam T. XIX, 1997, No 1 (34- 41) chi Crr hqc MEASUREMENT OF NATURAL TECTONIC STATE OF STRESS IN ROCK FOUNDATION BY BACK CALCULATION METHOD WITH DEFORMATION OF TUNNEL CONTOUR NGHIEM HUU RANH Institute for Water Resources Research) Vietnam 1. Introduction When designing construction in rock foundation, measurement of natural state of stress in rock mass is an important problem. The state of stress of rock foundation is defined by gravitational and tectonic force fields. The gravitational force field can not be separated from the rock materials. At any point in an elastic homogeneous isotropic rock mass gravitational components of stress field are defined by the formulas: a2 = ~~ = 1H, o-~ = cr~ = ug = ug = A1H, (1.1) (1.2) where cr~, 0'~, 0'~ - vertical and horizontal stresses of the point A; H - depth of the point A; 7 - volumetric weight of the overlaying rock layers of the point Ai A - coefficient of lateral pressure of rock mass at rest. The tectonic force field is significantly more complex than gravitational force field. It is related to the complex and non-uniform distribution of the rates of tectonic movement and the rate of strain of the earth crust. There are some methods for measurement of tectonic state of stress in rock mass. In this paper author represent a method of back calculation with deformations of tunnel contour that are measured in tunneling process. 2. Main idea of the method The tectonic component of stress field results from the continuous redistribution in spac~ of the tectonic movement and deformation rate of earth crust. It takes place in rock mass of tectonic zone and in igneous and metamorphic rock mass. When an underground opening is introduced in foundation, natural tectonic state of stress is redistributed The total stress around an opening ia resulted from induced stress called by man made activities and virgin stress or in-situ stress. It is changed in dependency on distance .