Deformation of huge thick compound key layer in stope based on distributed optical fiber sensing monitoring

In order to study the migration and deformation law of overlying composite key stratum in stope,based on the geological condition of Yima mining area,the position of overlying key stratum is determined by computer software (KSPB). Combined with Власов thick plate theory,the mechanics analysis and calculation are carried out according to the spatial relationship between the high position key stratum and the advancing length of the working face. A three- dimensional model (geometry size:3. 6 m×2. 0 m×2. 0 m) is constructed to carry out physical simulation test. In the simulation,the pressure sensors are used to test the abutment pressure in stope,the distributed optical fiber sensing technology (BOTDA) is used to monitor the dynamic deformation process of overlying stratum,and the multi-point dis- placement meter is used to test the internal displacement of strata. Thus,a comprehensive comparison analysis of the three measurement results is carried out. The results show that the theoretical values of the breaking interval of the composite key stratum are basically consistent with the measured values of the physical model test. The variation in value,position and shape of the frequency shift peak of the sensing optical fibers can reflect the dynamic evolution process of bending deformation,breaking and rotation of the overlying key stratum. When working face 1 is advanced to 960 m,the sensing fiber V11 ( located in the 40 m thickness fine sandstone sub-key stratum 112 m above the coal seam) occurs four frequency shift peaks,438. 98,313. 85,304. 27 and 288. 97 MHz respectively. The key stratum is fractured for 4 times,the initial breaking interval is 368 m,and the periodic breaking interval is 186 m,the key stratum is in caved zone. Sensing optical fiber V12 in the second group of the 160 m thickness conglomerate sub-key stratum (225 m above the coal seam) has a peak frequency shift of 165. 94 MHz,and the key stratum is fractured for only once. The initial breaking interval is 736 m,but the structure is not unstable and it is in the fractured zone. The maxi- mum frequency shift peak value of the sensing fiber V13(located in the 250 m thickness conglomerate key stratum 386 m above the coal seam) is 38. 61 MHz,which is much smaller than that of V11 and V12 . It occurs only minor bending deformation and is in the bending subsidence zone. The deformation law of overlying strata in working face 2 is basical- ly the same as that in working face 1,but the breaking interval of key strata in working face 1 is larger than that in working face 2. With the increase of mining scope,the super-thick composite key strata has fractured gradually from bottom to top,and synchronous and asynchronous fracture phenomena would occur,which increases the uncertainty and control difficulty of surrounding rock instability in stope and easily induces mine dynamic disaster.