Study Of Deformation Property And Settlement Prediction Of Soft Clay Under Coupled Dynamic Stress And Seepage Fields

With the deepening of the urbanization process,urban and rural infrastructure construction in China has entered a new vertical three-dimensional development and utilization stage.Engineering safety and environmental safety have become the fundamental requirements of major infrastructure construction in soft clay areas.The research shows that the poor engineering characteristics and complex construction environment of soft clay are key to cause engineering accidents.Once serious engineering accidents occur,they will cause huge economic losses and have a bad impact on the surrounding environment and society.In the complex environment of construction and service,soft clay bears the coupling action of dynamic stress field and seepage field(dynamic seepage coupling),and its mechanical behavior is different from that of single dynamic stress field and static stress field,showing complexity and uncertainty.Therefore,reasonable evaluation of the deformation characteristics of the soft clay under the dynamic seepage coupling condition and settlement prediction of the soft clay are important to minimize or avoid the geotechnical and underground engineering disasters.Taking the coastal soft clay as the research object and the deformation of soft clay as the core of the research problem,starting from the basic engineering characteristics of coastal soft clay,the deformation development of soft clay under the condition of dynamic seepage coupling was highlighted.And the constitutive relationship of soft clay under the condition of dynamic seepage coupling was established.Combined with the engineering practice,the paper put forward a multi-factor coupling settlement prediction formula of the soft clay ground bearing different tidal amplitudes,traffic loadings and tidal periods under the dynamic seepage coupling.Based on the multifactor coupling settlement prediction formula and grey prediction theory,the settlement prediction program of soft clay ground was developed.The research results are helpful to improve the scientific and technological level of reasonable evaluation and effective control of soft clay ground deformation in China,and provide scientific calculation methods and theoretical basis for safety prediction,evaluation and normal work of engineering construction in soft clay area.First,based on the sedimentary history,mineral composition and microstructure,a series of laboratory and in-situ tests were carried out to evaluate the engineering characteristics of coastal soft clay.The strength,permeability and deformation of coastal soft clay were analyzed.The relationship between the indexes of soft clay in the coastal area is established,which is practical for geotechnical engineers.The empirical relationship between undrained shear strength and depth,plasticity index was analyzed in tems of the strength characteristics;the correlation between permeability coefficient and pore ratio,consolidation pressure was described with respect to the permeability,and the variation development of permeability coefficient anisotropy coefficient was investigated;the compression index,consolidation coefficient,consolidation ratio,secondary consolidation coefficient and basic physical index were studied as to the deformation characteristics.The research results provide data support for the mechanical response analysis of soft clay under the condition of dynamic seepage coupling.Then,cyclic triaxial test was innovated,the back pressure was used to simulate the seepage pressure,and the cyclic loading motor is used to simulate the dynamic loading.The effects of osmotic pressure,cyclic stress ratio and cyclic number on the permeability and deformation of soft clay were studied systematically.Combined with static stress field and single dynamic stress field,the permeability of soft clay under the condition of dynamic seepage coupling were analyzed,the relationship between hydraulic conductivity and void ratio of soft clay was evaluated,and the prediction relationship between permeability coefficient and osmotic pressure,cyclic stress ratio and cyclic numbers under the dynamic seepage coupling was summarized.In addition,the deformation characteristics of soft clay under the condition of dynamic seepage coupling were compared and discussed,and the hysteretic characteristics,dynamic elastic modulus and accumulative deformation characteristics of soft clay were studied.According to different cyclic stress ratios and osmotic pressures,the empirical expressions of dynamic modulus and cycle number were proposed.Third,on account of the stress-strain hysteretic characteristics of the soft clay under dynamic seepage coupling,the soft clay presents cyclic degeneration characteristics when the number of cycles is small.Based on the critical state theory and the boundary interface theory,a generalized boundary interface equation was proposed by considering the relationship between the preconsolidation stress and the hydraulic conductivity.The model parameters adjusted the size of the boundary surface.The plastic modulus of the loading surface was obtained by using the consistency condition,and the dynamic constitutive model of soft clay was established under the dynamic seepage coupling.The dynamic constitutive subroutine program was developed by FORTRAN language.Compared with the experimental results,the correctness of the model was verified.The model can not only reflect the accumulative deformation and hysteretic characteristics,but also reflect the cyclic degradation of modulus during loading.Finally,a typical soft clay subgrade project in coastal area,which is subject to traffic loading and repeated water level,was selected to carry out field monitoring test and numerical analysis by combining the developed constitutive model with ABAQUS numerical analysis software.The center settlement,layered settlement,differential settlement of embankment and excess pore water pressure of soft clay ground were investigated to verify the correctness of the numerical model.Combined with numerical simulation,the influence of different tide amplitudes,traffic loadings and repeated water level periods on the center settlement of soft clay ground was researched,and the multi-factor coupling settlement prediction expression is constructed by hyperbolic fitting method.Based on the grey theory and the multi-factor coupling settlement prediction formula,the soft clay settlement prediction program under the condition of dynamic seepage coupling was developed by Visual Basic(VB)language,which realizes the function of grey prediction and multi-factor coupling soft clay ground settlement prediction.The prediction error can be controlled within 5%,which achieve the goal of accurate prediction.The research results provide theoretical and technical support for the settlement control and early warning of soft clay and scientific disaster prevention and mitigation under the condition of dynamic seepage coupling.