采场覆岩变形破坏模拟试验的光测方法对比

物理相似模型试验是煤矿采场上覆岩层变形破坏规律研究的主要手段,将BOTDA,FBG与DIC光测方法相结合,建立“点-线-面”的试验测试系统以提高测试精度十分必要。基于光测原理,分析了BOTDA,FBG和DIC技术的应变测量,探究了应变局部化带对DIC检测应变的影响,BOTDA和FBG测试本质上是一种“线应变”,而DIC是“面应变”。统计已有的试验研究,得出了不同工况下物理模型试验BOTDA,FBG光纤应变监测数据范围。搭建3 m平面应力相似模型,模拟煤矿工作面开挖77次,推进240 cm。通过埋设在模型内部的1根BOTDA传感光纤以及3个FBG传感器对模型关键层内部变形状态进行监测,同时以DIC实时观测模型表面变形,研究这3种不同的光测技术所获得的关键层应变测试结果,进行对比分析覆岩变形破坏规律,得出3种不同的光测技术测试应变的量化关系,并分析他们对应变测试存在差异的原因。试验结果表明,BOTDA和FBG的测试应变量级相同,在均匀连续变形区域DIC与BOTDA监测的应变比值为15.52~16.70,在非均匀变形区域DIC与BOTDA监测的应变比值为27~133;在应变曲线峰前阶段,DIC与FBG测试应变一致性好,峰后阶段DIC更好地反映了上覆岩层的变形;尽管在测试结果上有量级的差异,但随着岩层变形破断以及离层裂隙的张开、闭合,3种光测方法均可以反映岩层内外部同步性的变形,其发展趋势基本一致,BOTDA,FBG和DIC应变曲线峰值位置偏差较小;对离层出现位置,FBG的偏差为1.13%,FBG测试结果更好;对关键层破断范围,DIC测试的破断范围偏差为1.62%,测试结果更好。

Comparison of optical measurement methods for deformation and failure simulation test of overburden in working face

The physical similarity model test,combining Brillouin Optical Time-Domain Analysis(BOTDA),Fiber Bragg Grating(FBG)and Digital Image Correlation(DIC)optical measurement methods to improve the test accuracy,is the main method to study the deformation and failure law of overlying strata in a coal mine.It is necessary to establish a“point-line-surface”test system.Based on the principle of optical measurement,it is known that BOTDA and FBG test is essentially a“line strain”,while DIC test is a“face strain”,through ana-lyzing the strain measurement of BOTDA,FBG and DIC technologies,and exploring the influence of strain lo-calization band on the detection strain of DIC.After studying some previous experiments,the monitoring data range of fiber strain of BOTDA and FBG physical model tests under different working conditions was obtained.A 3 m plane stress similarity model was built,the extraction of the coal working face was simulated 77 times,and the coal working face was advanced 240 cm.Through one BOTDA sensing fiber and three FBG sensors embedded in the model,the internal deformation state of the key layer of the model was monitored.At the same time,the surface deformation of the model was observed in real-time by DIC.By studying the strain test results of the key layer obtained by these three different optical measurement technologies,comparing and analyzing the deformation and failure law of the overburden,the quantitative relationship of the test strain of three different optical measurement technologies was obtained.Then the reason of the difference between them was analyzed.It is shown in the test that the magnitude of test strain of BOTDA and FBG is the same,the difference of test strain between BOTDA and DIC in uniform continuous deformation area is 15.52-16.70 times in theory,and 27-133 times in non-uniform deformation area.At the pre-peak stage of the strain curve,the consistency of test strain between DIC and FBG is good,while at the post-peak stage,DIC reflects the deformation of overlying strata better.Although there is some difference in the test results,with the formation and deformation of the stratum,breaking and the opening and closing of the separation fractures,all of the three optical measurement methods can reflect the internal and external synchronous deformation with the basically same development trend.The deviation of the peak position of the strain curves of BOTDA,FBG and DIC is small.For the position of the separation,the FBG test result is better with a deviation of 1.13%.For the fracture range of the key layer,the fracture of DIC test is better with the range deviation of 1.62%.