Experimental Study On Creep Characteristics Of Deep Surrounding-Rock

As the major engineering materials the underground construction project confront with, rocks play an important role in the stability of rock engineering. Their substance components and complex geographical environments make them have significant rheological properties and evident timeliness. At present, experiment research is an inevitable foundamental work in the research of rock rheological propertites, whose results can provide the relevant rheology parameters to reveal the rheology attributes, build the rheological models, and analyse the data of engineering rocks. However, with the gradual increase of underground depth, there are different rheological properties between deep engineering rocks and shallow engineering rocks, which provides great challenges to engineering constructions. With such rationale, this thesis did an indoor creep experiment on the deep surrounding rocks of a mine, and the results were as follows:Firstly, it tested the basic mechanical characteristics of siltstones in deep surrounding rocks. The results showed that there were some joint fissures in siltstones, and its uniaxial compressions were mainly characterized as axial separation and partial shear faliure.When there was ambient pressure, the residual strength was relatively high and was mainly axial inclined shear failure after breaking the rocks. The higher the ambient pressure, the bigger the compressive strength of rocks. The relation formulas between ambient pressure and compressive strength of rocks, and the foundamental mechanical parameters of the rocks were gained in the test.Secondly, the research did several creeping tests under different ambient pressure on deep siltstones. The results showed that under uniaxial compress condition, creeping deformation and decay stabalizition time first decrease and then increase from low stress to high stress, creeping properties of rock gradually turned from strain hardening under into strain softening. The deformation modulus would decrease with the increasing of time and horizontal stress. However, the creeping rate would increase with the increasing of horizontal stress. Based on the contrastive analysis of creeping properties with different ambient pressure, it was found that the bigger the ambient pressure, higher the non-linear degree.Since the affects of fissure pressure closed was eleminated by ambient pressure in the process of creeping, the whole process presented a strain-softening phenomenon, and its deformation modulus affected by horizontal stress would not decrease with the increase of time. Some other results have also been found in the test. Increasing the ambient pressure can relieve the creeping faliure time. There was an obvious steady creeping stage before the breaking. The higher the ambient pressure, the bigger the deflection.Finally, the thesis identified the basic elements and combination modes probably existed in the rock creeping models on the basis of the load test characteristic curves in the siltstone homotaxial creep test. It analysed both merits and drawbacks of the common modes, proposed the modified visco-elastoplastic model, and determined its parameters by data fiting. As for the significant nonlinear and strain softening characteristics of siltstone axial creeping under the triaxial condition, this thesis defined "damage" through the changes of deformation modulus, established a creeping damage evolution equation, and modified the Burgers model. Moreover, it proposed the axial creeping damage constitutive model of siltstone in triaxial condition, and determined the model parameteres by comparing the test curves and fitting curves. The validity and viability of the model had also been be testified.