浅埋煤层隔水关键层失稳光纤传感检测试验研究

Water-resisting key strata stability detected by optic fiber sensing in shallow-buried coal seam

隔水关键层破断失稳是矿井水害及开采引起的生态脆弱区水资源破坏的根本原因,准确有效地对隔水关键层稳定性进行科学监测,是实现保水开采及岩层控制的重要基础。隔水层稳定性尚无有效直接监测手段,常采用钻孔探测、理论分析及数值模拟等计算导水裂隙带高度间接评判隔水层导通性。随着光纤传感技术的发展,将光纤布拉格光栅(FBG)、分布式光纤(BOTDA)等技术用于采动覆岩隔水关键层稳定性监测,为光纤传感技术在相似模型试验中的推广提供依据。研究表明:浅埋煤层当基岩厚度仅为60~67 m时,开采厚度为2 m的煤层时导水裂隙带将直接发育至地表,势必造成基岩含水层水体破坏,结构关键层裂隙被其上软弱岩层充填弥合具有一定隔水性,两侧断裂线及其附近发育的纵向裂隙成为主要渗流通道;分布式光纤检测应变因岩层断裂位臵应力集中而呈现"双峰"特征,峰值位臵与断裂线基本对应,可通过传感光纤预测采动覆岩破断线位臵分布;给出基于光纤传感检测的隔水关键层破断极限应变阈值为2000με;光纤光栅可对特定位臵岩体变形进行精准监测,检测隔水关键层破断失稳位臵与实际观测及分布式光纤检测结果基本一致。

The breakage and instability of the key water barrier strata is the fundamental cause of water damage and water resource destruction in ecologically fragile areas and mining water hazards.Accurate and effective scientific monitoring of the stability of water barrier key strata is an important basis for water-preserved coal mining and rock formation control.There is no effective monitoring method for the stability of the aquifuge.Drilling hole detection,theoretical analysis and numerical simulation are often used to calculate the height of water-conduction fractured zone to indirectly evaluate the aquifer permeability.With the development of optical fiber sensing technology,fiber Bragg grating(FBG)and distributed optical fiber(BOTDA)and other technology methods are used to monitor the stability of key layers of mining overburden and water barrier which provides a basis for the popularization of optical fiber sensing technology in similar model tests.The research have shown that in shallow seam,when the thickness of bedrock is only about 60~67 m and the thickness of coal seam is 2 m,the water-conduction fracture zone will develop directly to the surface of the ground,inevitably causing damage to the bedrock aquifer water body and cracks in key structural layers.The cracks in the key strata are filled by the weak strata and have certain water permeability.The fracture line and its longitudinal cracks nearby become the main seepage channel;the strain detected by optic fiber presents the"double peak"characteristic due to the stress concentration of strata in fracture position,and the peak position corresponds to the fracture line.It’s possible to predict the fracture line position by optic fiber sensor;the breaking limit strain threshold value of the water-resisting key strata based on optical fiber sensing detection is given as 2000με.The FBG sensor can be used to accurately monitor the deformation of rock mass at a specific location.The detection of instability position of the water-resisting key strata is basically consistent with the actual observation and distributed fiber optic detection results.