CORNER EFFECTS OF DEEP EXCAVATIONS WITH MULTI EXPOSED CORNERS IN SQUARE CROSSING OF UTILITY TUNNEL

The corner effect is one of the important forms of the spatial effect in deep excavations. However, the corner effects of the deep excavation with multi exposed corners have not been widely investigated and addressed in the previous literature. Based on the long and narrow deep excavation project of two square crossing of utility tunnels in a soft ground of Hainan, three dimensional numerical models of two typical construction programs are established using a commercial finite element software Plaxis 3D. Comparison and analysis of ground settlement caused by excavation, the deformation of the support structure, and the supporting axial force are performed. At the same time, the impacts of the corner effect on the distribution characteristics of these aforementioned studies are further discussed. The calculated results show that the maximum ground surface settlement of the long and narrow deep excavation for the utility tunnel varies between 0.11% H_e~0.67% H_e(H_e is excavation depth) under the two typical construction modes. The reasonable upper and lower bounds among the maximum lateral displacement of the steel sheet pile and excavation depth are 0.25% H_e and 1.35% H_e, respectively. On the whole, the maximum ground settlement of the soil around the excavation and lateral deformation of the supporting structure under the circumstance of construction program Ⅱ are lower than that in the condition of construction program Ⅰ. During the excavation process, it is worth noting that both two free surfaces of the exposed corner all have the remarkable corner effects under the circumstance of construction program Ⅱ, while the exposed corners in only one direction show the obvious corner effects under the circumstance of the construction program Ⅰ after their formation. The range of influence of the corner effects is approximately 2 times excavation depths. Within that range, the ground settlement, the deformation of the supporting structure and strut axial forces are all significantly lower than those in areas exceeding the coverage of the corner effects. The study suggests that if the influence of the corner effects and the degree of exertion are properly considered in the design of deep foundation pits with multi exposed corners at the intersections of utility tunnels, the project cost can be reduced to some extent.