Abstract: To overcome the difficulty of geostress measurement in high geostress environment, we discussed the optimization of narrow slot depth and slot layout by numerical simulation, and applied the method of geostress relieving by borehole slots to the stress measurement of Jinping projects’s underground laboratory. Numerical simulation suggest that when initial stress field is dominated by stress component parallel to the slot direction, the required depth of slot for complete release of stress on both sides of the slot reaches the maximum 16 mm. In field test, only one slot is arranged at a given depth in the borehole to improving the reliability of experiment and avoiding the mutual influence between the narrow slots. Meanwhile, the slot spacing is generally greater than 200 mm. The measured result shows that the rock mass at test site is in high geostress state, which is in accordance with the core disking in the process of drilling.

Key words: geostress relieving by borehole slot, geostress, slot depth, numerical simulation, Jinping underground laboratory