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.