Creep behavior of clayey soil and its model prediction in the Cangzhou land subsidence area

In the Cangzhou area of China, groundwater over-exploitation has led to serious land subsidence, and the creep deformation of aquitards has been monitored and found to be closely related to the development of land subsidence. The objective of this paper is to develop a computational model to reflect the creep deformation of aquitards in this area. Firstly, creep tests were conducted on clayey soils with burial depths ranging from 65.7 to 121.7 m. The results show that the total strain consists of three parts: instantaneous strain, primary consolidation strain and creep strain. Creep-time curves and isochronous creep stress-strain curves under stepwise loading were obtained by using the Boltzmann superposition principle, and both types of curves were characterized by nonlinearity, and the creep curves as a whole showed a trend of stable development. Secondly, on the basis of analyzing the advantages and disadvantages of the classical rheological models for clayey soils, a nonlinear creep model of NCE_CS that can take into account the influence of primary consolidation is proposed. The model contains five parameters, which can be solved by using genetic algorithm, and then a simple determination method of the parameters is proposed. Finally, by comparing with the test data and the calculation results of four classical creep models, it is confirmed that the NCE_CS model can fit the creep curves better. The NCE_CS model was also successfully used to estimate the creep behavior in another subsidence area located in Renqiu City in northwest of Cangzhou. This study will provide a basis for quantitative calculation of creep of clayey soils in the Cangzhou area.