Experimental Study On The Effects Of Pore Water Salinity On Physical And Mechanical Properties Of Soft Clay

The nature and composition of the pore solution will heavily influence the properties of the clay.Marine deposit's original sedimentary environment of high salt concentration of seawater has a great influence on its properties.External activities such as rainfall,groundwater movement during post-depositional process will change the salt concentration of the pore solution in the clay,especially for superficial sedimentary clay,the change and impact is more apparent.In this paper,salt adding and leaching experiments of soft clay obtained from Nanmendou Area,Fuzhou City are conducted to analyze the law and mechanism of the effect of different salt concentrations in the pore solution on the physical and mechanical properties of clay.The main research contents and conclusions are as follows.(I)Sedimentary experiments of salt adding and salt leaching are conducted to obtain sedimentary clays with different salt concentrations in the pore solution and desalinized clays,and regulations of the basic physical property parameters of these clays are given.Experiments find,a salt concentration less than 15g/L shows an obvious impact on the physical properties of clay,and liquid and plastic limits as well as plasticity index of the clays gradually increase with the increase of salt concentration,but liquid limit and plastic index decrease after salt leaching,while the variation of plastic limit in the test results is small,and these effects are concerned with the change of Zeta potential in the diffuse double layer.(2)The consolidation tests and permeability tests of reconstituted clays with different salt concentrations in the pore solution and desalinized clays are carried out to study the characteristics and mechanisms of these clays' consolidation properties and permeability characteristics.The tests indicate,with the same ratio of initial water content to liquit limit,the higher the salt concentration,the bigger the liquid limit of clay,and its compression curve locates higher,that is,the compression curve of clay with high salt concentration locates above that of clay with low concentration,but the hydraulic conductivity decreases with the increase of salt concentration in the pore solution;the attraction force and the repulsive force in the diffuse double layers between soil particles have a significant effect on the consolidation properties and permeability characteristics of clays;the influence of salt concentration can be described by liquid limit and explained by the the modified effective stress principle considering the attraction force and the repulsive force between soil particles;one-dimensional consolidation curve of clays can be processed by normalization with void index Iv,and the Iv-lg P isotropic consolidation lines are coincide with the intrinsic compression line ICL,but the Iv-lgkv curves can not be normalized to the same curve.(3)Triaxial consolidated-undrained shear tests of reconstituted clays with seawater concentration and desalinized clays are performed to compare the variation of the strength characteristics.The experimental outcomes show that the salt concentration of the pore solution in clay has remarkable effects on its constitutive relationship,failure envelop,stress path and undrained shear strength.Importantly,the study concludes,the higher the salt concentration,the higher the liquid limit of clay,and under the same effective consolidation pressure,the water content after consolidation becomes higher,and its corresponding undrained shear strength with the same water content after consolidation is higher,but the desalinized clay presents the opposite behavior.Moreover,the results also demonstrate,the undrained shear strength ratio R*su is heavily influenced by the salt concentration,and the value of R*su of high salt concentration is greater than that of low salt concentration.