Strain and Cracks of Tunnel Lining Surveyed by Fiber Bragg Grating Strain Sensors and Ultrasonic Tester

摘要

The cracks have emerged on the second lining of right tunnel for three months after tunneling in the Xin Chang Tunnel.The maximum crack depth is 264.0 mm which is explored by a RS-ST01C type ultrasonic tester.A fiber Bragg grating strain sensor is developed for measuring the surface strain of second lining.By converting the deflection of structure into the strain of displacement telescopic gauge,a fiber Bragg grating is mounted on two ends of gauge where suffers the strain,and as a result its Bragg wavelength will be shifted.The strain sensitivity and temperature sensitivity of the grating sensor are separately 0.677× 10-6/and 0.968× 10-5/°C.Gratingsensors are installed on the corresponding linings according to the crack distribution.In anobservation period of 51 days,the measurement results indicate that the lining cracks are derivedfrom the tilted pressure of surrounding rock.After a backfill period of 29 days,the tunnel structuresare gradually tending to be stability in the following operation period of 429 days.