Abstract: The soil-carrying effect is a unique overlying soil response mode in the construction of shallow-buried rectangular pipe jacking, a core risk source requiring key prevention and control in engineering, and a phased deformation response of overlying soil induced by the superposition and coupling of active and passive soil arching effects. To clarify the active-passive evolution law of the soil-carrying effect dominated by the over-excavation gap during pipe jacking and the influence characteristics of burial depth on it, the authors took the shallow-buried rectangular pipe jacking project of Sanyuanqiao as the prototype, proposed an active-passive progressive evolution model of overlying soil based on the over-excavation gap, and independently developed a scaled model test system for long-distance rectangular pipe jacking. Using transparent soil and digital image technologies, the authors carried out full-process transparent model tests of long-distance jacking under different shallow burial depths ranging from 0.30D to 0.90D (D is the width of the pipe), and systematically studied the active-passive state evolution, zoning formation law, long-distance accumulation characteristics and burial depth sensitivity of the soil-carrying effect dominated by the over-excavation gap. The results show that the over-excavation gap is a necessary prerequisite for the occurrence of the soil-carrying effect, and its spatiotemporal coupling with the jacking distance constitutes the macroscopic core mechanism of the effect. The soil-carrying effect exhibits a three-stage evolution characteristic of settlement zone, compensation zone and heaving zone, and evolves repeatedly under long-distance jacking, with the deformation amplitude of each event decreasing. The soil-carrying effect has high sensitivity to variations in burial depth: the overlying soil presents integral deformation in the shallow burial range of 0.30D–0.60D, and the shallower the burial depth, the more significant the deformation response; a decoupling phenomenon of deformation response between surface and deep soil exists in the range of 0.75D–0.90D. This study enriches the evolution mechanism of the soil-carrying effect in shallow-buried rectangular pipe jacking, and provides experimental support and theoretical basis for stratum disturbance control in shallow-buried rectangular pipe jacking construction and refined protection of surrounding buildings and structures.

Key words: rectangular pipe jacking, soil-carrying effect, over-excavation gap, progressive evolution, model test, transparent soil