Variation of In-Situ Stress with Depth: An Experience from India, Nepal & Bhutan

The in-situ stress measurements in rock are essentially required for the planning, design and analysis of underground caverns/tunnels for hydropower projects, infrastructure development, storage cavern, defence installations, recreational purposes etc. Knowledge of in-situ stresses is used for geometric design & orientation, support design; choice of liner, for deciding the grout pressure and choice of grout materials etc.Hydraulic fracturing test (HFT) method is one of the popular techniques used worldwide for better understanding of stresses. The stress measurements by hydraulic fracturing technique (HFT) were carried out for desilting chamber, surge shaft, pressure shafts and underground powerhouse complexes for hydropower development have been presented in this paper. The in-situ stresses data pertaining to 25 locations with depth varying from 80-1024m in Indian subcontinent, mostly from the Himalayas have been included.The variation of horizontal stresses in relation to vertical stress and influence of geological factors have also been studied and discussed in detail. The results of in-situ stress measurements were also compared with available correlations and geological interpretations. Finally, an attempt has been made to propose a correlation between maximum and minimum horizontal in-situ stresses with depth using above mentioned HFT data.