As a result of underground engineering in a certain level of in-situ stress condition of surrounding rock

the stress environment is different from the surface slope. It directly relates to the block stability analysis results which the block boundary normal stress quantification is correct or not. Study of block boundaries normal stress by field measurement is not common. Based on stability analysis of a large underground powerhouse block

several different direct boreholes are placed in the block and adjacent areas; the method of preexisting fractures reopening tests is used to determinate block boundary normal stress firstly; and the normal stress state and rules of spatial change of preexisting fractures that occurrence similar to block boundary are successfully acquired. Research results show that

after the completion of excavation

distribution of block boundary stress is not uniform

but with a certain rule; the normal stress of structural surface increases from shallow to deep in the vertical direction

and increases with the excavation surface distance increasing in the horizontal direction. The measurement data of normal stress are less than the calculated values based on the method of surrounding rock stress; but the overall consensus. The results provide references for determining block boundary condition and simplifying stress model.