硬、软煤样三轴压缩瓦斯流动特征

利用三轴渗流装置对来自不同矿区的硬、软原煤样进行常规三轴压缩渗流试验,对应力、形变、瓦斯流速连续采集,得出流速与主应力差、轴向应变关系曲线,从而得出硬、软煤样不同应力阶段的瓦斯流动特征,并且对瓦斯流动速度与主应力差之间的关系加以分析。结果表明:1)三轴压缩全过程中应力应变曲线变化趋势基本一致,可以被分为加载、破坏和残余阶段,加载阶段内软煤样环向应变高于硬煤样、吸收外界的能量相对较低,破坏阶段硬煤样应力迅速跌落;2)硬、软煤样在加载阶段内瓦斯流速与主应力差关系曲线都呈凹形二次曲线,残余阶段都呈线性增加;3)通过三轴压缩,硬煤与软煤的瓦斯流动规律表现出明显的差异,硬煤样表现为瓦斯流速显著增加,软煤样流速增幅不明显、甚至低于初始流速。

Gas flowing features of hard and soft coal seems under the 3-D compression stress

The paper is intended to make an exploration of the gas flow properties of hard and soft coal samples in the different stress stages through the normal 3-D compression and seepage tests,which can be conducted through a tri-axial seepage test via the tri-axial seepage equipment.In so-doing,all the data on the stress,deformation and the gas flowing rate can be collected and regulated successively during the whole test process so as to work out the corresponding curve of the gas flow rate with the principal stress difference and the axial stress strain.What is more,it is also possible to identify and determine the gas flow properties of the hard and soft coal samples in the different stress stages from the above tests.In addition,the paper has also analyzed the relationship between the flowing rate of the gas and the principal stress difference.What we have gained from the above studies can be illustrated as follows:First of all,all the trends of the stressstrain curve lines for the coal specimens in the whole progress can be found highly similar to each other,which can be divided into three stages,that is,the loading stage,the damage stage and the residual stage.However,the circumferential strain of the soft coal specimens has been found greater than that of the hard coal ones in the loading stage,therefore,its energy-adsorptive power from the outside turns out relatively low.It is just because of its lower energy-adsorptive power,the axial stress of the hard coal specimens tends to decline very quickly in the destructive stage.Secondly,the principal stress difference of the curve of the gas flow rates turns to be in a concave quadratic shape in the loading stage,but increase linearly in the last stage,that is,in the resid ual stage.Hence,a great difference can be found for the hard and soft coals in the end of the tri-axial compression test.For example,the gas flowing rate for the hard coal specimens has been dramatically increased by the end of the 3-D compression test,whereas that of the flow rate of soft coal specimens wouldn' t,and even turns to get lower than in the beginning flow stage.There fore,it can be concluded that the research results we have gained are in a position to provide a significant technical guidance for the soft coal seam with low permeability so as to find a prospect to in crease its permeability.