Abstract: Sanhekou Hydro-junction project is located in the river valley of east Qinling area. Complex geological structure and topography determines the complexity of in-situ stress distribution. To investigate the distribution of in-situ stress, hydraulic fracturing test was carried out on 3 boreholes in the slopes of both abutments and the river bed. Measured results show that the stress values are relatively large in buried depth of 0-50m in borehole at the river bed, and elevation of 500-530m in the boreholes at both banks, which can be designated as increased stress zone. Meanwhile, the area of buried depth under 50m in the borehole of river bed and elevation under 500m in the boreholes of both banks can be designated as original stress zone. In the shallow rockmass under the riverbed, the orientation of maximum horizontal principal stress is nearly perpendicular to the river trend, and with the increase of burial depth, it is close to the direction of regional structure. In the surface rockmass of slope, the direction of maximum horizontal principal stress intersects with the river trend at an small angle, and with the increase of burial depth, it transits to the northeast gradually. In deep buried rock mass, the direction of maximum horizontal principal stress is close to the regional tectonic.  

Key words: Sanhekou hydro-junction project, in-situ stress, regional tectonic 