酸化反应对煤矿顶板硬砂岩断裂行为的影响

Influence of Acidizing Reaction on Fracture Behavior of Hard Sandstone of Coal Mine Roof

煤矿顶板硬砂岩断裂力学特征及其裂化机理对于煤矿切顶具有重要指导意义。借鉴酸化压裂思想,对浓度5%、10%、20%盐酸溶液分别浸泡7 d、14 d的内蒙古准格尔矿区硬砂岩半圆弯曲SCB试样实施三点弯曲加载,获取了上述样品酸化反应后Ⅰ型断裂韧度、断裂压缩功及断口形貌前后变化特征,初步明晰了酸化反应对煤矿顶板硬砂岩断裂行为的影响机制。研究表明:加载位移载荷关系曲线显示砂岩试样断裂后阶段斜率较大,表明试样砂岩脆性显著,酸液浓度及反应时间对砂岩脆性影响不大但对砂岩宏观断裂前的曲线形态具有影响;随着浸泡酸液浓度增大砂岩试样断裂韧度KIC呈递减趋势,反应时间越长递减斜率越小,反应初期损伤效应最为显著;随着酸液浓度增加试样岩石韧度的弱化,断裂压缩功随之减小;随着酸化反应进行砂岩试样断裂形式由单一张裂过渡为张裂剪切破裂混合形式,酸化后硬砂岩断裂破碎效率提升;结合反应前后岩石矿物组成及微观形貌分析认为,酸液通过腐蚀砂岩中微斜长石、高岭石矿物形成缺陷,破坏矿物质点间的结合强度;酸化能够显著降低硬砂岩断裂能耗与岩石破碎难度,有利于提升煤矿切顶效率。

Fracture properties and cracking mechanism of hard sandstone roof are of great significance to caving.Based on the idea of acidizing fracturing,this paper applied three-point bending loading on hard sandstone SCB samples soaked in 5%,10%and 20%hydrochloric acid solution for 7 d and 14 d respectively,and the change characteristics of fracture toughness,fracture compression work and fracture morphology before and after acidizing reaction were obtained.The influence mechanism of acidification reaction on fracture behavior of hard sandstone roof in coal mine is preliminarily clarified.The results show that the displacement-load curve shows that the slope of sandstone sample at the post-fracture stage is large,indicating that the sandstone sample has significant brittleness.Acid concentration and reaction time have little influence on sandstone brittleness,but have influence on the curve morphology of sandstone before macro fracture.The fracture toughness of sandstone samples decreases with the increase of soaking acid concentration,and the slope decreases with the longer reaction time,and the damage effect is most significant at the initial reaction stage.The fracture compression energy decreases with the increase of acid concentration and the weakening of rock toughness.With the acidizing reaction,the fracture form of sandstone samples changes from single tensile fracture to tensile fracture and shear fracture,and the fracture efficiency of hard sandstone increases after acidizing.It is concluded that the acid solution corroded the micro-plagioclase and kaolinite in sandstone to form defects and destroy the bonding strength of the minerals.In this paper,it is considered that acidification can significantly reduce the energy consumption of hard sandstone fracture and rock crushing difficulty,which is beneficial to improve the efficiency of coal mine caving.