| The calculation and analysis on the foundation settlement of offshore artificial islands have determined results in engineering construction.Therefore,the study on the long-term settlement of artificial island has great theory value and engineering significance.In this paper,a large number of experimental and theoretical analyses were carried out to study the long-term settlement of a large-scale offshore artificial island which under construction.The main works includes:Firstly,the spatial distribution characteristics and the relations between the physico-mechanical parameters were statistical analyzed,which based on the geotechnical survey data;Secondly,the creep behaviours of undisturbed soils under different depth and stress condition were studied according to one dimensional creep test and drained triaxial creep test,and the creep equations were established;Thirdly,the settlement in and after construction were studied by the centrifugal model test,which considered the influence of design scheme,backfill loading and seawater level;Finally,the two dimensional full profile model of the artificial island was established,and the settlement was analyzed by the FEM program,which considered the consolidation,creep,Darcy flow,non-Darcy flow and non-uniform load.The main results are as follows:(1)Based on the statistical results of the physico-mechanical parameters,the relations between compression modulus and void ratio,compression ratio and water content,compressibility coefficient and water content,compression index and water content,void ratio and permeability coefficient,consolidation coefficient and plasticity index were established,and the equations provided convenience for parameters selected.The hypothesis testing results indicated that the distribution characteristics of the soil parameters have great difference between three elements,and merely part of parameters obeyed normal distribution.The discreteness of the shear strength index decreased evidently after Bayesian optimized.(2)The creep behaviours of clayey soils in different depths were studied by one-dimensional creep tests.The results showed that the strain and consolidation time increased with the increasing of consolidation pressure,and the void ratio decreased with the increasing of consolidation time and consolidation pressure.The primary consolidation is not completed until 100 min after consolidation pressure imposed.The secondary consolidation coefficient decreased with the increasing of consolidation time,and increased with consolidation pressure increasing.The secondary consolidation coefficient is approximately linear with the consolidation pressure.The ratio between the secondary consolidation coefficient and the compression index changed from 0.033 to 0.058.The creep equation was established which based on the test results and hypothesis B(consolidation and creep occurred in the meantime).(3)The drained creep behaviours of clayey soils in different depths were studied by drained triaxial creep tests.The results showed that the creep curves exhibit the characteristics of tenuation creep and contraction under low deviator stress,and showed the accelerated creep,contraction and dilatation under failure deviator stress.The deformation of clayey soils under deviator stress is basically stable within 4000 min.The axial strain rates decreased with the increasing of creep time,and increased with the deviator stress increasing.The deviator stress has little effect on the m value(slope of the curve).The improved Mesri equation was established based on drained creep tests results.(4)The long-term foundation settlement of the artificial island was studied by the centrifugal model test at 160 g acceleration,which simulated the prototype with 60 m sublayers and 22 m backfilled.The results showed that the foundation settlement attained 257 cm at the end of construction.After construction,the settlement rate is large from 0 to 1500 d and almost unchanged after 1500 d.The dissipation of the excess pore water pressure is faster in shallow layers,but slowly in deep layers.At the end of the test(about 15.8 years),the surface settlement reached 157 cm,and the consolidation degree in 12 m and 59 m attained 36.5%and 11.6%,respectively.(5)The long-term settlement of the artificial island was analyzed by numerical simulation.The governing equations and finite element equations were established under non-Darcy flow,and the non-Darcy flow module was compiled.The calculation model with 4000 m length and 63 m maximum depth was established to study the settlement and excess pore water pressure,which considered the consolidation,creep,non-uniform load,Darcy flow and non-Darcy flow.The results showed that the settlement distribution is uneven between functional areas at 100 years,which the maximum and minimum settlement is 288 cm and 197 cm,respectively.The dissipation of the excess pore water pressure in deep layers was slowly,and the dissipation rate in the terminal area and the soil surface area attained 78.5%and 31%,which indicated the foundation settlement is not finished,and enough attention should be paid.Compared with the Darcy flow,the settlement of non-Darcy flow is smaller,and the excess pore water pressure is larger,which indicated that the foundation settlement is delayed,and the consolidation time is extend under non-Darcy flow. |
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