Deformation characteristics and internal force analysis of shield hoisting construction of working shaft in silty clay strata: Case study in Jinan

Abstract

Unlike a conventional shield machine, a large-diameter shield machine needs to be hoisted separately with large hoisting equipment because of its heavy weight and large volume. Therefore, hoisting process control is important for the safety of the working shaft. By examining the shield hoisting of the Jinan Yellow River Tunnel project, this paper studied the influence of large-diameter shield hoisting on the working shaft in silty clay strata under the worst working conditions (358 t shield cutterhead load + 650 t and 300 t crawler crane loads). A three-dimensional numerical model was conducted to investigate the ground settlement, horizontal and vertical displacements of the retaining wall, and internal force in the process of shield hoisting. Field monitoring data were adopted to validate the results of the numerical analysis. The results showed that the following. (1) During the shield hoisting process, the ground settlement in the hoisting area was obviously larger than that outside it, whose maximum settlement reached 7.35 mm. (2) The horizontal displacement in the center of the retaining wall was the greatest, which reached 3.4 mm. When the depth of the foundation pit was 22 m, the maximum displacement was 9.2 mm. (3) The maximum bending moment was 1625.5 k⋅Nm, located at the foundation pit depth of 22 m, which was about two-thirds of the total pit depth. (4) The monitoring data showed that the maximum ground settlement during the shield hoisting was approximately 8.4 mm. The value was 12.5% different from the simulated maximum settlement of 7.35 mm. The maximum horizontal displacement value of the retaining wall was 5.2 mm.