32 / 2023-03-29 14:39:08

Experimental Research on Tunneling Surveys Combining GNSS and Terrestrial measurements

tunneling surveys,breakthrough error,GNSS,gyro theodolite,duo-linear joint chain

When tunnels are constructed from two opposite directions, it is necessary to estimate the breakthrough accuracy before the construction begins. Many articles about the analysis of tunneling survey have been published. However, the content of these papers was confined to theory, simulation or case summary. No experimental studies have come off the press.



For the construction of a super tunnel, the hierarchical surface control networks and underground duo-linear joint chain with gyro checks were designed, and the breakthrough error was estimated. In this paper, a systematic experiment research was conducted to verify the precision and to test the reliability of the analysis results. The surface and underground networks which were designed for the super tunnel project were set out at the experiment site, whose covering length is more than 7 km. The breakthrough error is required to be within ±35 mm. The surface network consists of ten points. The lengths of the sides near the same portal are similar, about 800 m. The underground network called duo-linear joint chain is composed of two double traverses. The breakthrough points, together with the surface points, were measured by means of GNSS. The underground network survey was conducted using total stations and gyro theodolites.



The analysis of the collected data revealed some useful conclusions. The coordinate differences and breakthrough errors calculated from the duo-linear joint chains in different experimental coordinate systems established by different methods are smaller than 25 mm, which has three implications: (1) an optimum reference system for the experiment was established; (2) the optimum configurations of the networks were designed and (3) the field observation scheme and the data processing methodology are effective. The contrastive analysis between the precision of different network configurations shows that the precision of the duo-linear joint chain points is 35% to 60% higher than the ones of traverse and 20% to 30% higher than the ones of double traverse. The precision improvement is significant and is consistent with the simulation results. In terms of the absolute size of the errors, the experimental results are significantly inferior to the theoretical estimates. Six gyro azimuths were measured separately with GRYOMAT 3000 and GAT Gyro Total Station. The coordinate and azimuth differences between the results calculated through the adjustment with and without gyro observations are relatively small. Considering the network’s length of about 6 km, the gyroscopic observations affect the adjustment results very slightly, which indicates that the duo-linear joint chain itself is high-precision and the accumulative errors are not significant. In another word, the gyroscopic surveying plays an important role in increasing the reliability rather than improving the precision when the underground surveying has sufficient accuracy.