Study On Engineering Property And Application Of Constitutive Model For Ningbo Soft Clay

With the rapid economic development since China embarked on the policy of reform and opening-up, various kind of projects such as urban infrastructures and civil architectures have been set up in soft clay areas. However, a large number of problems in Geotechnical Engineering, such as foundation settlement and stability, become the technical obstacle and restrict project construction at the same time. Therefore carrying out the study on property of territorial soft clay would have significant theoretical and practical value for project construction and economic development.Ningbo, as one of the first opening-up important seaports, which locates at southeast coastland and is the economic center in the south area of Yangtze River delta, has huge potential for development. However, previous research about Ningbo soft clay couldn't meet the demands for rapid economic development. For this reason, on the basis of the former researches, the thesis studied on engineering property and constitutive model for Ningbo soft clay by adopting methods of investigation, field measurement, laboratory testing and numerical analysis. The main works are as follows:Firstly, the thesis investigated and analyzed the engineering property of Ningbo soft clay. Based on the collected geologic data of Ningbo area and engineering geologic investigation reports from hundreds of projects, work results such as project geology of Ningbo, spatial variability laws of soft clay property parameters by means of probability statistical method, establishing experiential formulas between physico-mechanical indexes and summarizing engineering property of soft clay. Otherwise, the reasons caused the difference between Ningbo soft clay and other areas were analyzed from the points of geological origin, mechanical composition, mineralogical composition and micro-structure.Secondly, the thesis improved the determination methods of Geo-testing parameter. Based on the theory of Casagrande method, by adopting cubic polynomial and least square method to fit the compression curve, the preconsolidation pressure was determined through mathematical method and achieved the inquiring process by program. Besides, based on the theory of square-time method to acquire consolidation coefficient, by adopting least square method to fit the test curve and from the point of graphics to analyze the accuracy, a visual program was provided on the platform of commercial software.Thirdly, the thesis studied on engineering property of Ningbo soft clay by experiments. Based on the 24 consolidation tests and 70 triaxial shear tests, work results- such as stress history, structural property, creep property and influence factors affect the stress-strain relation were systematic studied. Meanwhile, specialties of Ningbo soft clay were pointed out by contrast with experiment results of others.Fourthly, the thesis studied on contrast of select constitutive model for Ningbo soft clay. Providing computing parameters of models such as Mohr-Coulomb model, Drucker-Prager model and modified Cambridge model by means of laboratory test, and adopting the program of ABAQUS to have numerical computation, conclusion was draw that modified Cambridge model was fit for Ningbo soft clay by compared the numerical computation results with actual measurement results. Besides, sensitivity of computing parameter in modified Cambridge model was analyzed.Fifthly, the thesis studied on constitutive model for Ningbo soft clay. For describing the structural property, by importing structural damage invariable and combined Shen Zhu-jiang theory of damage mechanics for geological materials with modified Cambridge model, an enlarged elasto-plastic damage model for Ningbo soft clay was presented and determining methods for parameters of this model were also provided. Meanwhile, for describing rheologic property, by combining the creep test and introducing the concept of delayed plastic deformation, thus, inelastic strain was divided into an instantaneous plastic part and a delayer visco-plastic part, an enlarged elasto-viscoplastic model was presented and determining methods for parameters of this model were also provided. Thereinto, instantaneous plastic part was acquired by modified Cambridge model and delayed plastic part includes volumetric creep and deviatoric creep, and the former is acquired by Taylor's secondary compression law, while the latter adopted Singh-Mitchell law. Furthermore, based on the platform of ABAQUS program, development process for UMAT subroutine program of elasto-plastic damage model and elasto-viscoplastic model were introduced.Lastly, the thesis studied on the application of elasto-plastic damage model for Ningbo soft clay. By adopting UMAT subroutine program of elasto-plastic damage model, study on application of this model was carried out through numerical analysis from the aspects of consolidation test and surcharge preloading test.