Creep Characteristics Of Coastal Soft Soil And Post-construction Settlement Of Subgrade

The soft soil in coastal areas of Tianjin is characterized by high water content,low penetrability,high compressibility,high sensitivity,large distortion and long duration,etc.,which are significant rheological properties.In calculating soft soil distortion,the soil's creep characteristics counts for much,so whether to consider the creep characteristics of soft soil not only produces different calculation results,but also leads to antipodal evaluation on the security of project.Thus,to explore the deformation behavior of soft soil creep and research the inherent mechanism of aging characteristics for soft soil distortion are very necessary to the project built on soft foundation.In the paper,the research on rheological theory is conducted.Based on the results of a series of laboratory creep test,two nonlinear rheological constitutive models described the littoral soft clay is proposed and the various parameters in the models are certained.Then via the Umat subroutine,combined with the engineering practice,the third planning road project which is located in Tianjin Nanjiang port is simulated to analysis the deformation mechanism of soft soil subgrade under the load of road fill,which uses the finite element software Abaqus.The main contents and conclusions are as follows:1.Microcosmic mechanism,constitutive,experiment and settlement of the soil rheology are summarized to analyzed the existing,where a key problem in the creep constitutive model of the application limitation in practical engineering is proposed and the influence of the soil lateral deformation and nonlinear problem are considered in the settlement.2.One-dimensional consolidation creep experiments under different stresses and triaxial consolidation creep experiments under different confining pressures and loading grades are carried out on the soft clay,and the full-process creep experiment curves have been obtained.Then the creep curves and stress-strain tautochrone have been analyzed systematically,where “Chen loading method” is adopted.It is found that the test curves are decaying-stable,and there is no accelerated failure.3.The rheological model theory has been analyzed and Merchant model is chosen to establish the nonlinear viscoelastic creep models based on one-dimensional consolidation creep experiments and triaxial consolidation creep experiments,which are applicable for Tianjin coastal area.Then the obtained gain 3D-modified Merchant models.4.Based on the above results,subroutines have been developed,respectively onedimensional consolidation creep experiments and triaxial consolidation creep experiments,which are correct because the calculation results of the unit model verification are consistent with experiments.At last,an engineer project has been analyzed by Abaqus.The results show that the settlements based on stress level and confining pressures,loading grades are similar in construction period.In the creep analysis,the reason why the former result is small compared with measured data is that one-dimensional consolidation creep condition is unconfined.While,the latter is fitting with the data,and creep settlement accounts for 46% in the total settlement on the 500 days after construction,indicating that the creep effect of the soft clay subgrade can not be ignored in the actual project.