Application of a type of strain block FBG sensor for strain measurements of squeezing rock in a deep-buried tunnel

摘要

Tunneling in squeezing rock often encounters large deformation, which threatens the safety and stability of tunnel support during tunnel construction. In this work, to acquire a greater amount of strain sensor data to fully understand the stress/strain state of surrounding rock during tunnel excavation, a special type of strain block with fiber Bragg grating (FBG) sensors has been introduced, which is characterized by three groups of FBG strain rosettes adhered to three adjacent surfaces of the block, respectively, and each strain rosette distributed in the form of a 0 degrees-45 degrees-90 degrees arrangement. Applying this type of FBG strain block sensor to a deep-buried tunnel in squeezing rock, six strain components in one strain block (representative of strain state of a point in rock) could be obtained with the processing method. The monitoring results can reflect the effect of tunnel excavation due to abrupt changes of strain monitored in rock, and were verified as being in reasonable agreement with numerical simulation. Therefore, the strain block with FBG sensors can be applicable in measuring strains in squeezing rock.