Study Of Construction Monitoring And Numerical Simulation On Banba Tunnel Of Hedu Freeway In Guangxi

The stress and strain of surrounding rock and supporting system in the tunnel construction change with time and space, which has always been the hot issue in academic and engineering research. Based on the Banba tunnel of Hedu freeway in Guangxi, adopting the field’s monitoring measurement and FEM as the instruments, this paper investigated the issue.Firstly, a brief introduction on the geological conditions of the Banba tunnel project, surrounding rock level and supporting structure had been conducted. Based on the actual situation to make the monitoring programs, on the regulatory requirements to collect data, using SPSS statistical analysis software to have a regression analysis on the monitoring data, the author got the regression equation of surrounding rock stress, lining contact pressure, bolt axial force, steel stress and two lining concrete stress. The regression analysis showed that there was a significant correlation between the surrounding rock pressure, internal force of steel stress and timing; and the excavation of the tunnel face had a more significant impact on the monitoring rock section and the supporting structure stress in the range of1.5times span of the tunnel. Moreover, the author predicted the extremum of rock pressure and supporting structure stress in line with the regression equation, and drew its distribution FIG along the tunnel’s cross-section.Secondly, based on the predicted extremum, judging by the ratio of supporting structure stress and the specification’s allowable value, the author evaluated the Banba tunnel’s rock stability and supporting structure’s safety. All of these came to the conclusion that the Banba tunnel’s rock was stable, both initial support and secondary lining had better safety reserve.Lastly, considering the hardening characteristics of sprayed concrete and tunnel rheology, adopting MIDAS/GTS software to have a numerical simulation on tunnel test section, comparatively analyzing the results of numerical simulation and of field monitoring, the author reached the conclusions as follows:first, horizontal tectonic stress in deep tunnel’s initial geo-stress is an important factor that can’t be ignored in numerical simulation, which can be simulated by combining Lateral stress coefficient method with the distribution of China geo-stress field and field data; second, the FEM results of anchor force, steel stress and sprayed concrete stress are basically consistent with the actual project, and its precision is high and can meet the project’s need; third, in the step construction, there will be obvious stress concentration in the temporary arch foot position after the excavation of rock on the up stairs, so in the weak surrounding rock segment construction, the rock on the down stairs should be excavated timely, so as to form a closed arch, meanwhile, to avoid the prolonged time which can cause the expansion of surrounding rock’s plastic zone and then lead the shear failure of surrounding rock; fourth, the influenced range of spatial effect which generated by the excavation of tunnel face is about1.5times of the tunnel span, if over this distance, rock rheology will play a major role in the internal force of supporting structure.