Research On Creep And Relaxation Properties Of Deep Rock Masses In Jinchuan No.2Mining District

With the expanding economy and great progress in science and technology in our country, in purpose of meeting the needs for resources and production space, human beings are exploring higher room in space as well as deeper room in underground space. Especially in the case that excavation of mineral resources starts from superficial part to deep part. However, deep rock masses have characteristics of high ground stress, high temperature and high permeability, which behave obvious rheology in common. Meanwhile, deep rock masses, which are soaked in underground water for a long time, can be changed by aqueous solution microscopically in mineral constituent and mask pattern structure, after which interstices and dissolution cracks are found in rock masses, and they both have influence on seepage rate and pore pressure and change the mechanical properties such as strength and stiffness of rock masses on the view of macroscopic. At the same time, they will result in unstable deep rock masses and accelerate the failure of wall rock and lead to the bodily injury or property damage.The paper combines experimental study and theoretical analysis and researches into basic mechanical and rheology properties of deep rock masses in Jinchuan No.2mining area and focuses on creep and relaxation experimental study of rock masses on conditions of natural and water-saturated states. The paper analyzes the influence of water on rheology of rock masses macroscopically and introduces the rheology foundation model which can reflect nonlinear visco-elastic plasticity of deep rock masses. The main contents in this paper are listed as follows:(1) Collect deep rock samples in Jinchuan No.2mining area, process them into standard test pieces and do basic tests such as uniaxial compression test, shear test and swell test. And then analyze the regularity for change of compressive strength, deformation modulus and Poisson’s ratio in test piece and also study the deformation features, strength characteristic and failure law of rock samples, after which basic mechanical parameters are obtained. (2) Creep experiments on deep rock samples under conditions of natural and water-saturated states are conducted using multi-step incremental loading and unloading method. According to the curves and data from creep experiments, make data analysis and data cleansing in terms of recoverable instant elastic strain, hysteresis visco-elastic plasticity, unrecoverable instant anelastic strain and visco-plastic strain, and then obtain rheology features of deep rock masses under high stress.(3) Relaxation experiments on deep rock samples under conditions of natural and water-saturated states are conducted using multi-step incremental loading method. The results of the experiment indicate that continuous relaxation law and non-continuous ladder-type relaxation law are found through relaxation curves. From the analysis of relaxation stress parameters, it can be found that with the increase of strain levels, initial stress rate, initial stress value, steady stress value and relaxation amount of stress increase and meanwhile steady stress ratio decreases.(4) Introduce a foundation model with stress threshold which can describe nonlinear visco-elastic plasticity of deep rock masses in nonlinear accelerated creep process and adopt damped least square method to fit creep and relaxation curves in terms of model equations, after which each value parameter can be got. Test curves and theoretical curves can fit well, which shows that the model is able to describe creep and relaxation features of deep rock masses well in Jinchuan No.2mining area.