Abstract: Compared with other soil layers, the risk of shield tunneling in water-rich sand is greater, but the mechanism of sand deformation caused by shield tunneling is currently unclear. Relying on an electric power tunnel project in Guangzhou, this paper selects a typical water-rich sandy stratum section for high-frequency, close-range monitoring of stratum deformation caused by shield tunnel construction. The following understandings are obtained, which can be used as reference for similar projects. 1) In a water-rich environment, compared to in a homogeneous sand layer, in a combination of fine and coarse sands, the tunnel is more prone to seepage failure. Under this circumstance, the fine sand layer bears greater seepage force while being strongly supplied with water from the coarse sand layer, and the fine sand layer is thus very easy to be eroded or even hollowed out. 2) The ground deformation caused by uniform volume loss and local concentrated loss is quite different. In the case of uniform loss, because the arching effect is not as strong as the local loss, the disturbance range, surface settlement and horizontal displacement are all larger. The location of the maximum horizontal displacement is also closely related to the heterogeneity of the formation loss. When the formation loss is uniform, the maximum horizontal displacement on both sides of the tunnel occurs within the tunnel elevation range; but when the uneven loss (partial collapse of the tunnel top) occurs, the location of the maximum horizontal displacement will move up significantly. 3) The seepage force expands the range of stratum disturbance. 4) The stratum loss rate is severely affected by grouting. The vicinity of the tunnel is large, the ground surface is the smallest, and the soil above the tunnel tends to loosen.

Key words: shield construction, soil deformation, sand stratum, field monitor, numerical simulation