煤壁应力峰值动态移动诱发封孔漏气机理研究

On the mechanism of sealing leakage due to the stress peak dynamic displacement in front of the coal workface

基于有效应力原理分析了煤体吸附瓦斯对煤体强度的影响,提出应用煤体单轴抗压强度衰减比k_σ表征瓦斯压力变化对煤体强度的影响;应用数值分析方法研究了煤体瓦斯抽采前后煤壁前方煤体应力、屈服破坏范围的变化。结果表明,抽采期间,煤壁前方煤体应力峰值处于"动态移动"状态,致使煤壁前方的屈服破坏区间同时发生移动,水泥封孔段由受压转为应力卸载状态而发生膨胀破坏,在封孔段水泥与煤壁之间形成松动漏气通道,孔外空气将沿该漏气通道进入孔内,使抽采浓度降低。为提高带压封孔方法的封孔效果,应科学判定抽采前期煤体应力峰值区间,并考虑抽采期间煤体"应力峰值移动"的影响,在应力峰值区间适当向两侧延伸封孔段长度,注重封孔器材和封孔材料的研制和选择。

This paper is aimed to its study results on the impact of the stress peaks dynamic movement on the borehole sealing leakage in the front of the coal face. For this purpose,we have observed and analyzed such impacts of the gas adsorption on the coal strength based on the principle of the effective stress. And,consequently,we have proposed a hypothesis of the coal uniaxial compressive strength decay ratio k_σto describe the effect of the gas pressure on the coal strength. Here we have found that,the decay ratio k_σtends to be increasing with the decrease of the gas pressure,which keeps to increase the coal strength. What is more,letting k_σ= 2/3,we can work out the stress and the yield failure region changes in the front of the coal face via a numerical simulation. Thus,the results of our investigation and simulated study show that the stress peaks in the＂dynamic movement＂state in the front of the coal face during the gas extraction,there exists the likeliness for the yield failure to take place due to the movement of the gas extraction region simultaneously. What is more,destruction or expansion of the cement sealing segment due to the stress change from being compressed to unloaded. Moreover,leak channels may also come about between the cement sealing segment and the borehole due to the air leakage into the borehole along the leak channels,which may account for the lower concentration of the gas extraction. To make up for the sealing effect of the borehole pressurized,we have put forward a proposal that closer attention has to be paid attention to the following measures：First,it is of great accuracy to determine the stress peak range in the early gas extraction,with the sealing segment increasing the length in the direction of the coal face affected by the stress peaks movement. And,secondly,focus has been put on improving on the sealing means and materials. Sealing facilities should be made convenient in installation with available sealing materials. Including the liquidity,expansibility and solidified strength.