There are many problems

great danger

and great difficulty in controlling deformation when constructing a shield tunnel in water-rich sandy stratum.On the basis of a case study of the shield tunnel of Nanchang Subway

adopting the finite difference software（FDM）FLAC to establish three-dimensional mechanical model to simulate the dynamic process of shield construction in water-rich sandy stratum condition and combining with the actual measurement date

we analyzed the ground settlement caused by shield tunnel construction.The analysis results indicate that transversal ground settlement induced by shield construction was assumed as a V-shaped curve

the location of maximum ground settlement was situated above the tunnel center

and the width of the settlement tank was about 6D.Longitudinal ground settlement induced by shield construction was assumed as an S-shaped curve.The ground in front of the excavation surface uplifted and behind excavation surface settled.The ground deformation behind excavation surface decreases gradually with the increase of distance from the excavation surface.The supporting force has significant influence on soil stability on excavation surface and ground settlement reduction.There are high risks when the shield settles in and draw out.So we should take corresponding measures in practical engineering to ensure construction safety.The conclusion can provide useful reference for design and construction of subway tunnels in Nanchang.