Abstract: The data of traditional manual measurement of shield tail gap are delayed and cannot directly reflect the changing trend of the shield tail gap. Accordingly, automatic shield tail gap monitoring technology is developed. The doublechannel laser is taken as a prefabricated ruler, the shield tail tube image is obtained through an industrial camera, and the shield tail gap value is calculated according to the pixel distance after image processing. The test technology recommended can measure the changes in the shield tail gap in real time during shield tunneling and has been applied and tested in several projects. The field test results show the following: (1) The automatic noncontact measurement technology can realize oneclick measurement of the shield tail gap, and the test process does not affect the normal construction of the shield. (2) The measurement device can monitor the shield tail gap in real time, simulate the ellipticity of the shield tail, and monitor the deformation of the shield tail and the space status of the shield tail and the tube. (3) The acquisition device adopts a dual laser transmitter, which can accurately establish the geometric relationship of the actual distance and the pixel distance and improve the test accuracy of the measuring device. The monitoring accuracy can be controlled within 3.8 mm.

Key words: shield tunnel, shield tail gap, image recognition; real-time measurement, double-channel laser