Study Of Distribution Rule Of Wall Rock Block Boundaries Normal Stress Based On Reopening Test Of Preexisting Fractures

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.