The Creep Characteristics Of Coal Mine Gob Roof Rock Series And Test Model Under Condition Of Underground Gas Storage

Accident in coal mine gob roof is one of the main disasters in mining process, it may cause significant economic losses and put ecological environment and life safety of workers on threat. The greater the percentage of roof rock such as mudstone, sandstone and sandy mudstone, the greater the deformation of roof rock, and the more sophisticated the gas storage conditions. Roof rock creep has great impact on the stability of gob roof.In terms of the creep instability of gob roof rock series under condition of underground gas storage, uniaxial compression creep test of mudstone, sandstone and sandy mudstone were conducted by using RLW-2000 rock microcomputer-controlled rheology servo test system. The combined model which is suitable for roof rock series is determined by analysis of classic rheological model and Matlab least-square fitting operation. Based on the characteristics of roof rock series rheology and improvement of classic model, the seven-element nonlinear elastic-plastic constitutive model was established. Finally the model was proved by the experimental data by Matlab least-squares iteration method, and the main results are as follows:(1) When the external load is less than the yield strength, the creep of roof rock includes initial creep and stable creep, micro porosity closed while new crack is generated by the break down of micro particles. With tine goes on the deformation of roof rock changes very small and be stable gradually. When external load is greater than yield strength, the creep of roof rock accelerates, the particles are destroyed and the connection between particles are severely weakened, micro cracks eventually develop into macro cracks and lead to the broken of roof rock.(2) It can be seen from the experimental data that the strength of sandstone is biggest, mudstone comes the second and sandy mudstone is minimal. The reason is that the sandy mudstone is between sandstone and mudstone, two kind of particles with different size could not cement compactly.(3) Least-squares iteration was conducted on Poynting Thomson model, generalized Kelvin model, Burgers model and Kormanura model based on experimental data, the results show that Burgers model has better fitting effect. Burgers model can describe the initial creep and stable creep of roof rock series very well, but it has some deviation with actual situation. In order to simulate the creep of roof rock series, Burgers model was improved.(4) When external load is greater than yield strength, the creep of roof rock accelerates. In order to describe the accelerate stage of roof rock series, nonlinear viscous elastic-plastic rheological model of roof rock series is necessary. A new seven-element model can be get from the series of sticky plastic model and improved Burgers model which can comprehensively reflect the creep property of roof rock series.(5) The one dimensional creep equation of the seven-element model is derived and the model was proved by the fitting operation of experimental data. The results show that the data is basically above the fitting curve and the mew model could describe the whole process of the creep of roof rock series. It can be seen from the comparison of the three fitting curves that variance of sandy mudstone is minimal while that of mudstone maximal. This indicates that the seven-element model could describe the creep of roof rock series very well, the softer the rock the better fitting effect and the description of creep property.