Abstract: The measured statistical results show that the settlement of immersed tube tunnels during construction accounts for more than 50% of the total one and is mainly caused by compression of the base layer. Based on the prototype of Shenjiamen Port immersed tube tunnel in Zhoushan, a 1:10 scale shrinkage model is established for the longitudinal length of 30 m focusing on the formation process of sand base layer in marine environment to study its compression process under different deposition conditions and to assess the impact of back silting. The results shows under no silt gravel, the compressibility modulus of the overall base layer is 3.41 MPa, indicatings the poor compression performance of base layer. Under different concentrations of back silting, the compressibility modulus of the base layer ranges from 1.54 to 3.89 MPa, mainly about 2.34 MPa, about 0.69 times that without back silting. The silting acts like lubricant which increases the interleave of sand and gravel, extends the compression settling time, increases the compression amount of base layer and enlarges the regional inhomogeneity.