In-situ experiment on deep shaft under-water excavation using a shaft sinking machine in Shanghai

The shaft sinking machine (SSM) method has recently emerged as a promising alternative for constructing ultra-deep shafts in densely populated urban areas, offering advantages such as minimized spatial footprint, high efficiency, and precise verticality control. However, the distinct cyclic hydraulic loading conditions imposed on the prefabricated segmental lining system and the associated soil–structure interaction during SSM construction remain insufficiently understood. To address this gap, this study investigates the load characteristics, lining behavior, and ground responses based on comprehensive field monitoring data from an ultra-deep shaft project in Shanghai. The analysis reveals pronounced non-uniformity in circumferential soil pressure, with a coefficient of non-uniformity between 0.65 and 0.90, and highlights a clear arching effect in deep strata where the vertical pressure gradient is significantly reduced. A suspension force model is proposed to estimate the frictional resistance along the shaft wall, which is generally below 5 kPa due to circumferential over-excavation, and the model provides reliable predictions of the maximum suspension force. Furthermore, internal water pressure is shown to govern the structural response of the lining, inducing outward expansion during excavation and inward compression after dewatering. Ground deformations are closely linked to construction activities, with excavation interruptions and water-level reductions causing substantial settlement. These findings clarify the mechanisms governing soil–structure interaction under SSM conditions and provide practical guidance for the structural design and construction strategy of ultra-deep shafts in soft ground.