Mechanism Of Rock Deformation Memory Effect Based On Viscoelastic Frictional Sliding

The determination of the in situ stress is very important.The deformation rate analysis(DRA)is an in situ stress determination method based on the rock deforamtion memory effect(DME).Many international experimental results verified that the DRA method is a potential method in determining the in situ stress.However,the history of the DRA method is very short,it needs more improvements.The lack of research on the mechanism and theoretical model prevents the correct interpretation of experimental data and improvements of the DRA method.This paper proposed a new mechanism for the DME: viscoelastic frictional sliding over the microcrack interfaces and grain boundaries.The main contents are as follows:(1)Detailed introduction of DME and the procedure,the calculation method,the key techniques of the DRA method were given.(2)The physical experiments were performed on three materials: sandstone,Fuji Rock and volcanic sediment.It is verified that,there was rock deformation memory effect in the stress region below the crack initiation.Characteristics of the axial and later DRA curves were given.The experimental results provided basis for the following theoretical model.(3)Proposed a new mechanism of the DME: the viscoelastic frictional sliding over the crack interfaces and grain boundaries.Theoretical model in 1D was developed by the combination of elastic elements,St.Venant bodies and dashpots.Three special loading regimes were performed on the 1D model and the following physical phenomena were well explained: the formation of the DME,the memory fading effect,the influence of rock types,the holding time,the repeated preloads,the artificial memory,in situ stress memory and so on.Results were in accordance with physical experimental results.From above,the frictional sliding was verified that can produce the DME.At the same time,many improvements of the DRA method were proposed.(4)Axial symmetric model was developed.Loading regimes in the axial direction were performed on this model.Results show that,the 3D model has the same ability to produce the DME and the lateral strain can be used in the DRA method and has the same accuracy with the axial strain.Then,two loading regimes with confined stress were carried out on axial symmetric model.Results show the stress collected by the DRA method in the axial direction is the combination of the axial stress preloaded and the confined stress.Based on the results,a new application of the DRA method was proposed.