Experimental study of the precursor information of the water inrush in shield tunnels due to the proximity of a water-filled cave

Abstract

A water-filled cave can easily result in the deterioration of the surrounding rock when a shield tunnel passes through the urban karst area, resulting in engineering disasters such as water inrush, ground collapse, and shield machine malfunction. To study the surrounding rock stability due to the proximity of a cave with confined water, we carried out a large-scale three-dimensional geo-mechanical model test on a tunnel that was excavated by a compound EPB (Earth Pressure Balance) shield machine based on the metro tunnel in the “spring city” of Jinan. We developed a new 3D printing technology for a water-filled cave and a new method for the 3D laser reconstruction of surface settlement monitoring. The multi-physics evolution information, including the soil moisture content of the muck, the displacement, the stress, and the seepage pressure, were obtained and proven consistent with each other. The results showed that the water inrush mainly resulted from a shield tunneling disturbance in conjunction with the confined water in the cave. The process of water inrush in the surrounding rock could be divided into three stages, which included the initial stable period, the variation period with the shield tail passing through, and the final stable period. The rock ahead of the excavation face was characterized by two stages, which included the initial stable period and the sudden collapse of the water-resistant slab. Compared with the tunnel excavated by drilling and with the blasting method, the water inrush triggered by the EPB shield machine tunneling was observed to be more hidden and catastrophic. The displacement and the seepage pressure comprised the most intuitive precursor information. These test results can provide a theoretical basis and guidance for the water inrush prediction for being triggered by a single confined cave with no inter-connections.