Abstract: Real-time measurement of deep three-dimensional geostress field distribution and disturbance law are very important for the engineering analysis of rock mass stability. However, there lacks the mature testing technology and supporting instruments for measuring the ground stress in weak surrounding rock at depth. The article firstly introduces in details the fundamental principles and technology of the rheological stress recovery method of the ground stress test for deep soft rock. Then in-depth theoretical analysis is carried out to study the rationality of sensing units’ layout of the rock mass pressure sensor. The results show that if the three sensing surfaces of the upper hemisphere of the six-direction pressure sensor are set to be perpendicular to each other’s normal direction, the three sensing surfaces of the lower hemisphere cannot be arranged perpendicular to each other’s normal direction; if the three sensing surfaces of the upper hemisphere are set to be perpendicular to each other’s normal direction, the three sensing surfaces’ normal direction of the lower hemisphere cannot be parallel to the three sensing surfaces’ of the upper hemisphere, and two of the three sensing surfaces of the lower hemisphere cannot have their normal directions perpendicular to any of the sensing surfaces’ normal direction of the upper hemisphere, three sensing surfaces of the lower hemisphere cannot be close to perpendicular to each other, and the cosine of the normal direction and the x, y, z axes are preferably not much different. If the three sensing surfaces of the upper hemisphere are not perpendicular to each other, a layout design is considered with the three sensing surfaces of the upper hemisphere having their normal directions set at an angle of 45° to the horizontal plane and those of lower hemisphere set at an angle of 30° to the horizontal plane, and the angle of the sensing surfaces’ the normal directions of the upper and lower hemispheres projected on the Oxy horizontal plane to be 60°. The calculation results show that this arrangement is one of the arrangements that are scientifically sound.

Key words: rheological stress recovery method, pressure sensor, sensing units, orientation layout