实时低温条件下露天矿饱和损伤煤系砂岩动态力学特性及其破坏机制

Dynamic mechanical properties and failure mechanism of saturated coal-measure sandstone in open pit mine with damage under real-time low-temperature conditions

我国许多大型露天煤矿都地处新疆等西部高寒地区,低温环境下边坡岩体中的自由水发生冻结,对损伤岩体的宏微观结构将产生显著影响,使岩体的力学性能进一步劣化,进而诱发大规模滑坡等地质灾害。因此,开展含有初始损伤的饱和煤系岩石在低温条件下的动态力学特性及破坏机制研究,对寒区露天煤矿边坡稳定及安全开采具有重要意义。利用实时低温分离式霍普金森压杆(LT-SHPB)试验系统,对含初始损伤的含水饱和露天煤系砂岩开展了低温冲击加载试验,并结合扫描电镜观测,对其动态力学特性及细观断裂机制进行了系统研究。研究结果表明:①随着冲击速度(强度)的提高,砂岩动态抗压强度、弹性模量及峰值应变均快速增大,表现出显著的冲击强化效应;同时,在固定冲击速度下,抗压强度与弹性模量随初始损伤呈逐渐减小的趋势,砂岩的损伤弱化特性显著,而峰值应变则表现出损伤强化特征;②冲击载荷作用下砂岩破坏程度随着初始损伤及冲击速度的增大逐渐提高,破坏形式呈现出由张拉破坏向粉碎性复合破坏的转化特征;③较常温环境,低温环境下含水饱和损伤砂岩发生显著的冻胀作用,细观上表现为砂岩内部缺陷尺度与缺陷数量增多,其为砂岩动态力学特性产生劣化的根本原因;④砂岩动态破坏形式主要表现为脆性破坏,而在较高初始损伤下,砂岩内部出现了细观韧性断裂形貌,局部韧性断裂显著,当砂岩损伤值由0增加到50.26%,砂岩脆延性系数均呈现出快速增大的变化特征,表明其动态断裂模式呈现出从脆性破坏向韧性破坏的发展趋势。

Many large open-pit coal mines in China are located in the western alpine-cold regions such as Xinjiang Province.The freezing of free water in the rock mass of the slope under low temperature environment will have a significant impact on the macro and microstructure of the damaged rock mass,causing further deterioration of the mechanical properties of the rock mass and thus inducing large-scale landslides and other geological disasters.Therefore,the study of the dynamic mechanical properties and damage mechanisms of saturated coal measures sandstone containing initial damage under low temperature environment is of great significance to the stability of slopes and safe mining of open-pit coal mines in the cold regions.In this paper,using the real-time low-temperature separated Hopkinson pressure bar(LT-SHPB)test system,the low-temperature impact loading test was carried out on the water-saturated open-pit coal measures sandstone with initial damage.Combined with the observation of SEM,its dynamic mechanical properties and meso fracture mechanism were systematically studied.The results show that①with the increase of impact velocity,the dynamic compressive strength,elastic modulus and peak strain of sandstone increase rapidly,showing an obvious impact strengthening effect.At the same time,under the fixed impact strength,the compressive strength and elastic modulus gradually decrease with the increase of initial damage,showing an aboriginal damage weakening characteristics,while the peak strain shows some damage strengthening characteristics.②Under the impact load,the failure degree of sandstone gradually increases with the increase of initial damage and impact velocity,and the failure mode presents the transformation characteristics from tensile failure to comminuted composite failure.③The low temperature environment will have an obvious frost heaving effect on the water-saturated damaged sandstone,resulting in an increase in the scale and number of defects inside sandstone,which is the fundamental reason for the deterioration of the dynamic mechanical properties of sandstone.④The dynamic failure mode of sandstone is mainly brittle failure.Under high initial damage,the meso-scale ductile fracture morphology appears in the sandstone,and the local ductile fracture is obvious.When the damage value of sandstone increases from 0 to 50.26%,the brittle ductility coefficient of sandstone shows a rapid increase,indicating that the dynamic fracture mode presents a trend from brittle failure to ductile failure.