To use the hole diameter variation method using the partial stress release method by parallel drilling in determining the initial plane stress state of the rock mass, the stress state change surrounding the main measuring hole by parallel drilling is derived and the results are verified by numerical simulations. In the partial stress relief method based on parallel drilling method, firstly, the main measurement hole is drilled to appropriate depth, and then the sensor which is designed and developed to measure the diametrical deformations in three different directions (in general they are apart 120° from each other) is installed in the main hole to sense the hole diametrical change, and then multiple parallel stress relief holes (approximately four at 90°) are drilled at regular intervals next to the core without drilling a larger hole which has coincident center with the main hole as in the complete stress relief method. The diametrical change due to the release of stress surrounding the main measuring hole is then measured using the diametrical deformation gage and through them the initial plane stress state of the rock mass is determined. The numerical simulation results of this method show that the reliability of the partial stress release method compared to the full stress release method can reach more than 99%.
Ri et al. (2026) studied this question.