A comparative study of optical measurement methods for deformation and failure simulation test of overburden in working face

The physical similarity model test,combining BOTDA,FBG and 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 FBG and BOTDA 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 15.52-16.7 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%.