Quantitative Experimental Study On Factors Influencing Structural Soft Clay

The naturally structural clay is characterized by high void ratio,compressibility,water content and low permeability,shear strength.In China,there is abundant soft structural clay underlying the coastal cities,where a lot of infrastructures have been being constructed.The naturally structural clay would lead to significant foundation settlement or differential settlement.Therefore,understanding the structural characteristics of soft clays and what influences them are helpful for solving the settlement problems and providing theoretical basis for scientific construction design and reasonable handling of emergency accidents.In this research,some artificially structural clays were fabricated in an innovative way and were taken as the objective.A series of compression tests were conducted to study the effect of initial void ratio(IVR),inter-particle cementation strength(CS)and pore size distribution(PSD)on the compression characteristics of the structural soft clay.The microstructure differences of the artificially structural clay with various initial states are analyzed by SEM and MIP.Based on the grey correlation analysis method,the relationship between the coefficient of structural characteristics(CSC)and the microscopic parameters is revealed.The results show that:(1)When the cementation is weak(cement ratio=5%),with the increase of the IVR,the structural yield stress(SYS)decreases significantly(Max-Min=128.70kPa);the post-yield compression index(PYCI)firstly increases and later remains unchanged;the CSC firstly increases and later decreases.The PSD has great effect on the SYS(Max-Min=39.94kPa),while has little effect on the PYCI.When the cementation is strong(cement ratio=8%),as the IVR increases,the SYS decreases(Max-Min=39.11kPa);the PYCI and CSC increase greatly(Max-Min=0.045 and 1.13,respectively).The PSD has little effect on SYS,PYCI and CSC(Max-Min=5.17kPa,0.007 and 0.18,respectively),while has great effect on post-transitional deformation.As the CS increases,the SYS and the CSC rises obviously(Max-Min=110.56kPa and 1.43,respectively),the PYCI firstly increases and later remains unchanged.The compression curve in the log(e+1)-log?_v'plot shifts from a typically three-stage shape to a new three-stage shape,in which the compressibility within the third stage is higher than that in the second stage.(2)The general structure of artificially structural samples is mainly composed of aggregates comprising small clay platelets.The contact modes among the soil particles are mainly line-to-surface and surface-to-surface,and the orientation is not obvious.With the increase of the initial void ratio,the number of the interaggregate pores increase obviously,the porosity increases,and the number of pores decreases.The dominant pore group changes from intra-aggregate pores to interaggregate pores.The initial void ratio has little effect on the roughness of the pore surface.With the increase of cement content,the cemented materials bind more small clay particles together,resulting in the decrease in the interaggregate pores and the increase in the intra-aggregate pores.However,the cement content has few effect on the porosity.On the other hand,the increased flocculated cemented materials lead to the rise in roughness and the decrease in the pore orientation.Controlling salt content is able to change the pore size distribution of the soil.The higher the salt content,the larger the number of the interaggregate pores.The increment curve of the pore size distribution gradually shift from the single-peak mode to the double-peak mode.(3)The influence of the microstructural parameters on the structural coefficient is significant,and the order from strong to weak is respectively probability entropy,porosity,pore number and fractal dimension.The greater the probability entropy of samples,the worse the order of the pore arrangement,and the stronger the structural characteristics of the soil.The larger the porosity,the greater the proportion of the pores in the soil.Under the external forces,the soil particles are easier to dislocate and the variability is greater.The fractal dimension of pores indirectly reflects the roughness of soil particle surface.The rougher the surface of the soil particles,the greater the cohesion and friction between the soil particles,the stronger the stability of the soil.