Abstract: In-situ stress condition is one of the essential information of stability analysis and engineering design for underground caverns, and it is particularly important for safety assessment of underground engineering in deep and high-stress condition as well as disaster prevention. Taking Jinping underground laboratory in China (CJPL) buried at a depth of 2 400 m as an example, the principle and method of in-situ stress measurement under high stress based on overcoring method have been expounded at first. Furthermore, some technological improvements are given: 1) Adopting new drill and overcoring gradually to reduce the extent and scope of stress concentration at the roots of the cores; 2) Using large diameter drill to increase the thickness of the hollow cylindrical core, namely increasing the time that fracture needs to cause the rock core to break; 3) Drilling exploration hole near the measuring points to get the integrity condition and to evaluate the feasibility of the test. After theoretical explanation, plane stress state, perpendicular to borehole axis with different depths and three-dimensional stress state are given to analyze original stress field and stress redistribution led by excavation. Verified by the relationship between stress distribution and damage of surrounding rock as well as the result of numerical calculation, the result of three-dimensional stress is proven to be reliable and can be used as a basis of further scientific analysis, engineering stability evaluation and design of disaster prevention.

Key words: in-situ stress measurement, overcoring method, underground laboratory, high stress, rock core disking