Pore Water Salinity And Sand Fraction Effect On Engineering Behavior Of Soft Clay And Its Mesoscopic Mechanism

Land resources are scarce in the coastal areas of Jiangsu province,and land reclamation methhod is used in the construction of port engineering.The soil type formed by hydraulic reclamation is often a mixture of sand and clay because of the influence of the original soil layer and the reclamation process.The land of this area is formed under the marine sedimentary environment,and it has high pore water salinity.The general engineering design does not consider the influence of salinity change on the engineering properties of hydraulic fill soft clay,but in fact,with the seepage of surface water or groundwater,salinity leaching will bring potential harm to the reclamation project,such as lower bearing capacity,increase of ground deformation.In this study,the physical properties,consolidation behavior and shear strength of sand-clay mixtures with a variety of pore water chemistry were investagted,thereafter the probabilistic FED was applied to clarify its internal mesco mechanism.The main contents and results are as follows:(1)To investigate the effects of sand content and salinity content on paticle size distribution of sand-clay mixtures,the laser analyser test and hydrometer test were conducted.By using the liquid plastic limit test,it is found that the liquid limit of the sand-clay mixtures was obviously reduced with the salinity addition,but the degree of reduction weakened with the increase of salt concentration.The higher liquid limit,and the greater change degree of the liquid limit change on the salinity effect of the soils with the higher the bentonite content.The addition of salinity reduces the plastic limit and plasticity index of sand-clay mixtures,and decreases the water holding capacity.(2)To investigate the effects of sand content and salinity content on compression behaviors of sand-clay mixtures,one-dimensional consolidation test was conducted.The results show that the compression curve with the high sand content is below the compression curve of the low sand content,the compression curve of sand soft clay has obvious inflection point near 400 kPa,where the curve begins to decrease slowly,and the compression index decreases obviously.At this time,sand particles may contact each other and form the sand skeleton,and restrain the compression deformation.When other conditions are controlled,the coefficient of consolidation and permeability increase with the increase of sand content;On the other hand,the soil compression curve of the higher salt concentration is lower.Before the sand skeleton is formed,the compression behavior of the mixed soil is mainly controlled by the clays,where the salinity effects are obvious.After the sand skeleton is formed,the compression behavior is mainly controlled by the sand skeleton.(3)The CU triaxial tests were conducted to investigate the effects of sand content and salinity content on the strength properties of clays.The results show that the increase of sand content and the addition of salinity enhance the shear strength of clays,especially the friction angle.These additions improve the slope of the critical state line and strength.(4)The consolidation test and undrained triaxial tests were simulated by the probabilistic finite difference method(FDE,FLAC3D).In view of meso scope,the formation of sand skeleton and the change law of shear zone can be observed.After the comparison of the numerical simulation and laboratory test suggested the probabilistic FDE can be adopted to clarify the behavior evolution of these special soils.