Strength versus particle size.

Backfill mining is an effective way to solve environment pollute, surface subsidence, and groundwater system damage which caused by coal mining. However, the complex underground environment may change the physical and mechanical properties of the backfill body, which poses a risk of strength failure. This paper analyzed the failure of gangue-based cemented backfill body which made up of gangue and fly ash. The results show that physicochemical reactions will generate quartz, kaolinite, and other high-strength substances; hydration reaction between the fine particles will generate hydrocalcium silicate and other C-S-H gels, they wrapped gangues as a whole, which provide a high strength of the cemented backfill body. Several experiments were carried out in order to find the reason for failure in samples under loads. The conclusion drawn as following: (1) When the load is large, the cracks extend from the surface of the samples to the interior, at the same time, the length and width of the cracks increasing obviously and connecting as net. Especially the external load exceeds the peak intensity. (2) The relationship between sample failure and pores is weak, but obvious with crack development, especially the cracks connected as a net. (3) The interface structure formed by gangue is an important source of crack development and, thus, will stimulate the development of cracks.

充填采矿法（Backfill mining）是解决煤矿开采引发的环境污染、地表沉陷及地下水系统破坏问题的有效手段。然而复杂的井下环境会改变充填体的物理力学性质，进而带来强度失效的风险。本文针对由煤矸石与粉煤灰（fly ash）配制而成的煤矸石基胶结充填体（gangue-based cemented backfill body）的失效特性展开分析。研究结果显示，物理化学反应会生成石英（quartz）、高岭石（kaolinite）等高强度物质；细颗粒间的水化反应会生成硅酸钙水合物（hydrocalcium silicate）及其他C-S-H凝胶（C-S-H gels），此类凝胶可将煤矸石整体胶结包裹，为胶结充填体提供高强度支撑。为探究载荷作用下充填体试样的失效诱因，本文开展了多组试验。所得结论如下：(1) 当载荷较大时，裂隙会从试样表面向内部扩展，同时裂隙的长度与宽度显著增加并相互连通形成网状结构，尤其当外载荷超过试样峰值强度时，该现象尤为突出。(2) 试样失效与孔隙的相关性较弱，但与裂隙发育程度显著相关，尤其是当裂隙连通形成网状结构时。(3) 煤矸石形成的界面结构是裂隙发育的重要诱因，进而会加速裂隙的扩展。