Study Of Settlement And Its Control Method Of Submarine Immersed Tube Tunnel Caused By Rheology Of Lower Soil Layer

This paper takes the Shenzhen to Zhongshan cross-river immersed tunnel project as the engineering background.Through the uniaxial compression creep test,the creep characteristics of the soft soil under the immersed tube tunnel are studied in this paper.Based on the creep test law,the Burgers creep constitutive model was selected to describe the rheological characteristics of the soft soil in the lower lying soil.The model parameters of the Burgers model were obtained by fitting the creep test data.Combined with the parameters of Burgers creep constitutive model,the settlement law of the immersed tube tunnel was analyzed by using FLAC3D model,and concrete settlement control measures were put forward according to the settlement calculation results.The main research methods and results are as follows:(1)The silty clay samples in the lower soil layer of the E25?E29 pipe section and the clay samples in the bottom of the E1?E5 pipe section of the immersed tube tunnel between Shenzhen and Zhongshan were collected.The density p,water content ?,soil particle gravity Gs,cohesive c,internal friction angle ? and uniaxial compressive strength ? of the silty clay and clay are measured by indoor experiments.(2)The uniaxial compression creep tests of silty clay and clay were carried out,and the creep laws of silty clay and clay were obtained.It was found that the rheological properties of these two kinds of soil were very large.The proportion of creep deformation in the total deformation was concentrated between 83%?94%.The creep rate of silty clay was very large in the first 3?5 hours,while the creep rate of clay was large in the first 6?10 hours,and then the creep rate decreased rapidly and tended to stabilize.(3)The characteristics and applicability of the typical creep model were analyzed.According to the creep test rule,the Burgers model was selected to describe the creep characteristics of the soft soil under the immersed tube.First,the creep equation of the Burgers model in one dimension state was used to fit the test data,and then the creep parameters of the Burgers model in the three-dimensional state were obtained by using the transformation relationship of the elastic and viscous creep parameters.(4)Based on the creep parameters of Burgers model,the numerical simulation of FLAC3D was used to analyze the settlement law of the immersed tube tunnel.The deformation law of the lower lying layer and the settlement law of the immersed tunnel were analyzed under the condition of rheology and without considering the rheological condition when the lower lying layer is the silt clay or the clay soil.Then,they were compared with the settlement of the immersed tunnel when the underlying layer is sandand considering the rheology of the stratum of the immersed tunnel crossing.The results showed that when the lower lying layer is silty clay,the deformation of the lower lying layer and the settlement of the immersed tube tunnel are both larger than that of the clay.Under the rheology condition,the deformation of the lower lying layer and the settlement of the immersed tube tunnel are larger than that under non-rheological condition.The immersed tube tunnel at the junction of the lower Stratum layer is the soft soil and the non-soft soil will produce larger uneven settlement.It is necessary to reinforce the soft soil foundation.(5)The factors causing settlement of immersed tunnel are analyzed from two aspects of internal and external reasons,and control measures of immersed tunnel settlement are given out in the construction period and the operation period respectively in this paper.Combined with the distribution of lower soil layer and the settlement calculation results of "Shen zhong channel" immersed tunnels,the foundation treatment scheme is given.