Abstract: The information of the in situ stress is stored in the rocks after excavation. The deformation rate analysis (DRA) method is used to determine the in situ stress based on the rock deformation memory effect(DME). Cracks generation and propagation under the previous load was initially assumed to be the mechanism of the rock DME. However, this mechanism can not explain many phenomena in the rock DME. The lack of a theoretical model prevents the correct interpretation of experimental data and improvements of the DRA method. The physical experiment is firstly performed on a volcanic sediment sample. It is showed that the in situ stress in the low stress region can be determined by both the axial strain and the lateral strain, while the DRA curves by these two kinds of strain are same. Then, the frictional sliding over the crack interfaces and grain boundaries in rocks are proposed as the mechanism of the rock DME in the low stress region. Based on this mechanism, a theoretical model using elastic element viscous element and St. Venant bodies is constructed. Cyclic compressions with different peak stresses and delay time are performed on the theoretical model. Results show that, not only the formation of the rock DME is well explained but also many DME phenomena are observed, such as the memory fading and the accuracy of the DRA curve by the lateral strain as the same as the axial strain. All the results by the theoretical model are in accordance with the experimental results. By the theoretical model, the frictional sliding over the crack interfaces and grain boundaries is verified to be the mechanism for the rock DME in the low stress region. Moreover, the results by theoretical model provided a basis for the improvement of the DRA method in the determination of the in situ stress.

Key words: deformation memory effect (DME), deformation rate analysis (DRA), in situ stress determination, frictional sliding, memory fading