Abstract: Herein, the Plaxis-3D software is employed to simulate the Shuanghua road tunnel crossing beneath the existing Chengdu metro line 10 and the Chengdu-Guiyang high-speed railway tunnel structures within typical Chengdu strata, revealing the deformation impact mechanisms and curtain barrier effect of a large-diameter shield tunnel undercrossing existing underground structure clusters. The research findings are summarized as follows: (1) At a design burial depth of 2.4D (where [D denotes the tunnel diameter) and without any reinforcement measures, the settlements of the existing structure clusters exceed the code-specified limits. Increasing the burial depth of the newly built tunnel correspondingly reduces the settlements of the existing structures, bringing them to within the allowable limits when the burial depth is increased by 2D. The implementation of grouting measures (180° and 360° coverages) to reinforce the new large-diameter tunnel considerably decreases the settlements of the existing structure clusters. Compared to 180° grouting, 360° grouting provides the most pronounced settlement control effect. However, 180° grouting also effectively controls settlements within the allowable limits. (2) For the Chengdu-Guiyang high-speed railway tunnel with its straight wall-arch section, the most pronounced deformation during excavation occurs at the base slab. The lateral displacements at the bottom-left and bottom-right corners of the base slab are nearly coincident, whereas their vertical displacements alternate in precedence as the undercrossing progresses. (3) The ovality of the circular cross-section of the existing Chengdu metro line 10 tunnel shows an overall decreasing trend along the undercrossing. The decrease is most notable as the new tunnel approaches and gradually stabilizes as it moves away. (4) By comparing the ovality changes of the cross-section when only one metro tunnel exists, it can be observed that the degree of ovality decrease of the existing tunnel clusters reduces. This indicates that the interaction within the tunnel clusters diminishes the impact of the new tunnel′s undercrossing on the existing underground structure clusters, demonstrating the existence of a curtain barrier effect.

Key words: super-large-diameter shield tunnel, existing underground structural clusters, adjacent construction, curtain barrier effect, cross-sectional ovality, numerical simulation