Calculation of unusual stratum load for metro tunnel crossing active ground fissure considering different intersection angles

Abstract

How to determine the unusual stratum load for metro tunnel under the influence of ground fissure is a major challenge faced by the construction of Xi'an Metro in China. In this paper, based on the theories of Bierbaumer and Terzaghi, a limit equilibrium form of stratum holding effect principle is proposed as an alternative solution for calculating the unusual stratum load experienced by metro tunnels crossing ground fissures at different intersection angles. Our methodology uses the movement mode of stratum-tunnel induced by active ground fissure to construct the analysis model, while considering soil properties and strength, holding force, tunnel buried depth, segment diameter, and the intersection angle between tunnel and ground fissure. Fundamental formulae for the development of soil fracture angle during this movement process are also derived and analyzed. The methodology is also illustrated and validated by two representative examples, and the sensitivity of parameters affecting the results is discussed as well, providing some design suggestions for practical engineering. The presented alternative way of calculating the unusual stratum load in the active ground fissure site might be helpful for the design of metro engineering to meet the necessary degree of safety.

Keywords

• Metro tunnel
• Ground fissure
• Unusual stratum load
• Soil fracture angle
• Intersection angle