Study On Physical And Mechanical Properties Of Soft Clay Considering The Influence Of Salinity

In recent years,with the rapid development of China's economy,the demand for land in coastal areas is increasing.A large number of civil and industrial buildings and infrastructure have to be built on the soft clay foundations;especially the implementation of coastal beach reclamation projects has gradually become an important way to ensure the implementation space of coastal strategy.Due to the high porewater salt concentration and fully saturation in the initial sedimentary environment,marine soft clay exhibits some special engineering properties.Long time temperature,rainfall and sea level rise will lead to the change of salinity,which will have a fundamental impact on the engineering characteristics of soft clay.Insufficient consideration in the project design will constitute a potential safety hazard.Therefore,systematic macro and micro tests and theoretical analysis are needed to carry out investigating the influence of salinity on the physical and mechanical properties of soft clay,and focusing on the interaction between the salt concentration of porewater solution and the soil and water.It is expected to provide experimental data and theoretical basis for deepening the understanding of mechanical behavior of marine soft clay,and provide reference for solving practical engineering problems.The main efforts and conclusions are summarized as below,(1)Through X-ray diffraction and Atterberg limit tests,it was found that the Lianyungang soft clay mainly composed of illite-montmorillonite mixed layer and illite mineral.The liquid limit and plastic limit decreased to some extent as salinity increases.When the salinity is low,the change of liquid and plastic limit is more significant.With the increase of salinity,the change of liquid and plastic limit tends to be stable.The plasticity index of soil shows a similar decline law with that of liquid limit as salinity increases.(2)One dimensional consolidation test results showed that the compression curve of remolded soil with high salinity is located below that with low salinity,and the increase of salinity reduces its compressibility.The void index of samples at different salinities can be normalized to the ICL and EICL lines.Under the action of salt flocculation,the compression index of soil decreases,while the consolidation coefficient and permeability coefficient increase significantly along with the increment decreases with the increase in salinity.(3)The triaxial CU test results showed that the stress-strain curves of soft clay samples with different salinities show strain hardening behavior.The higher the salinity,the higher is the curve.The total and effective angle of internal friction (?) and (?)'increased obviously,and the increasing range decreased as the salinity reaching 2%.The critical state stress ratio M of soil increased significantly,and the CSL line of clay specimen at each salinity can be determined by the empirical formula of effective internal friction angle (?)'.Under the same normalized water content,the effect of salinity on the undrained strength of soft clay is obvious,and the undrained strength at each salinity changes basically near the IS_uL line.(4)The directional analysis of clay microstructure showed that the soil agglomerates under the action of salt flocculation,which changes from the obvious overlapping form of sheet structure to the dense agglomerating of block structure.This is the essential reason for the increase of the internal friction angle of the soil during the shearing process and the increase of the shear strength of the saline soil.The pores between the massive soil particles are connected with each other to form a larger drainage channel,so the consolidation coefficient and permeability coefficient of the soft clay specimen at high salinity can be improved in the macro test.(5)The quantitative analysis of microstructure showed that with the increase of salinity,the particle area of soft clay increases and the pore area decreases.With the agglomeration of small particles,the roundness of particles increases.The order of pore arrangement increases and the orientation of pores decrease.When the soil particles change to a massive structure,the fractal dimension of pore distribution gradually decreases with the increase of salinity,and the pore distribution tends to be centralized and collectivized.