Comparative tests on section steel and steel grid for loess tunnels with large section

The excavation area is about 160 m2 in the loess tunnel of Zhengzhou-Xi’an high-speed passenger railload, so it is necessary to study different application effect of the section steel and steel grid. It is of important significance to identify the application situation of the section steel and steel grid for the design and construction. Comparative tests are adopted. For the good comparability of the experimental results, the tunnel which has the similar experimental condition is chosen. The Hejiazhang Tunnel is taken as the experimental section in which the section steel and steel grid of 40 meters in length are set, respectively. The main comparison included the settlement of tunnel crown and arch foot, horizontal convergence, surrounding rock pressure, stress of initial supporting steel framework, etc. It is indicated: the section with the steel grid has more settlement and mostly equal horizontal convergence than the one with the section steel; there are less stresses in the steel grid than in the section steel and the former has relatively uniform distribution of stresses; the value of soil pressure is commonly small; but the soil pressure is much higher in the steel grid. After 4 steel frames (3.2 m) of the tunnel are excavated, the settlement of the steel frame reaches about 26 percent of the total settlement and the maximum stress is about 33 percent of the total stress. It is shown by the analysis that the steel grid and section steel are both applicable to the tunnel in the viscous old accumulation loess of degree IV, but steel grid is more advantageous.