不同瓦斯压力下煤岩三轴加载时蠕变规律及模型

Creep law and model of coal under triaxial loading at different gas pressures

岩石蠕变模型众多,其适用性及优缺点亟待总结,而且低瓦斯压力与煤岩蠕变间的关系尚不确定,为此,进行了低瓦斯压力下分级加载轴压时型煤蠕变实验。结果发现,随着瓦斯压力增大,型煤轴向应变增大,说明煤岩蠕变与瓦斯压力呈正相关。利用实验数据检验常见蠕变模型时发现经验函数(幂函数、指数函数、多项式等)均存在缺陷,只能拟合衰减蠕变或非衰减蠕变中的一种;Burgers模型及其改进模型均存在不足,西原模型不适用于非衰减蠕变,西原加速模型适用于砂岩,用于拟合煤岩非衰减蠕变时存在滞后性。经过优化后得到改进的西原加速模型,经证明其可靠性强。另外,提出了蠕变拐点的观点,岩石发生非衰减蠕变是蠕变曲线上至少存在1个蠕变拐点的充要条件。这不仅完善了蠕变的数学理论,而且能为预防岩石失稳破坏等工程实践提供借鉴。

There are too many creep models at present,but none has summarised these models＇ applicability,advantages and disadvantages yet. Also,the relation between coal rock creep and low gas pressure is unclear. Therefore,the creep test of coal rock under different gas pressures at triaxial stress was carried out to study the influence of gas on creep,and the applicability of various common creep models. The results show that the larger the gas pressure is,the greater the axial strain of coal and rock. The coal creep is positively correlated with the gas pressure. Then,the experimental data were used to test these common creep models. It was found that the empirical equations,such as the power function,exponential function and polynomial function,can only fit one of the decay or non-decaying creep. The Nishihara model cannot fit the non-decaying creep,and the Burgers model and its improved model has a few defects in fitting the decay and non-decaying creep curves. The Nishihara acceleration model has hysteresis,when it is used to fit the non-decaying creep of coal rock. And the Nishihara acceleration model is suitable for sandstone creep but not for coal rock creep. In this paper,the Nishihara acceleration model was improved. It is concluded that the improved Nishi-hara acceleration model can better describe the creep of coal rock. In addition,the theory of creep inflection point was presented. The creep curve at least has one creep inflection point,which is the necessary and sufficient condition for the non-decaying creep of rock. It not only enhances the theory of acceleration creep,but also has some guiding significance to prevent rock steady failure and other engineering practices.