Centrifugal Model Test Study on the Mechanical Characteristics of Shield Tunnels Influenced by Different Types of Openings for Cross Passages

Abstract

To investigate the mechanical characteristics of shield tunnels when openings are made for the construction of cross passages, a series of centrifugal model tests were conducted. The segmental features of the shield tunnel were simulated in the tests, and the influence of different types of openings, namely, rectangular opening, small circular opening, and big circular opening was compared. External earth pressures, structural deformations, dislocations, and structural stresses were monitored during the tests, while the influence of different buried depths was also investigated. The results show that (1) soil arching effect occurred in the overlying soil due to the deformation of the tunnel, and the earth pressure reduction coefficients can guide the tunnel structural design; (2) vertical deformations of the main tunnel and the dislocations between adjacent rings increased with the opening sizes significantly; (3) significant stress concentration occurred close to the openings, and the compressive stress at the inner surface may even exceed the limit strength of the concrete. In summary, the adverse responses of the tunnel increased with the increase of the buried depth and the opening size. Targeted measures should be taken, such as temporary support, longitudinal connections, and high-strength materials near the openings.

Modification of the Peck Formula for a Double-Track Shield Tunnel under Expressway Subgrade

“…Therefore, it is necessary to predict stratum deformation before construction, monitor it during construction, and observe it after construction for an extended period of time. In light of the formation settlement caused by shield construction, scholars around the world have contributed various research methods: some scholars used Peck's empirical formula [1,2] to predict the formation settlement; other scholars derived analytical solutions based on certain assumptions and constitutive relations [3,4]; numerical analysis [5,6] and simulation tests [7,8] are also widely used in settlement prediction. The Peck empirical formula is the most commonly used method to predict surface subsidence in practical engineering.…”