The paper introduces method of determining natural stress (horizontal stress) of the rock mass to serve for calculation and clarification of the low stress possibility along headrace tunnel for the design of the scope of tunnel reinforcement lining.


In the foundation rock mass, determination of value and direction of natural stress plays a very important role in assessment of physico-mechanical characteristics of the foundation rock mass and it is especially important in calculation to determine precisely the required supported extent in construction of underground works.

Presently, there are three methods of stress measurement: convergence measurement method, overcoring method and hydraulic fracturing method.

The hydraulic fracturing method is a popular method for determining minimum principal stress in the rock mass, and especially, it is effective and the most economically when measuring at great depths where can be reached only by a borehole.

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