Deformation Characteristics And Microstructure Mechanism Of Heavy Metal Contaminated Clay Under Chemo-Hydro-Mechanical Conditions

With the acceleration of China’s urbanization and the upgrading of industrial structure,enterprises in heavy polluting industries such as metal smelting have been closed and relocated,resulting in a large number of heavy metal contaminated sites left in China.Due to the chemo-hydro-mechanical coupling effects of heavy metals,rainfall evaporation,underground runoff and overburden,the mechanical properties and microstructure of soil have evolved.In this paper,the red clay widely distributed in southern China was taken as the research object.Through laboratory tests and theoretical analysis,the deformation characteristics and microstructure mechanism of heavy metal contaminated clay under chemo-hydro-mechanical conditions were systematically studied.This study is financially supported by National Natural Science Foundation of China（42072318）and the National Key Research and Development Program of China（2019YFC1805905）.The work and main research results are as follows:（1）Through saturated penetration tests of heavy metal solution,the deformation characteristics of compacted red clay under the infiltration of heavy metal solution were studied.The results show that the compacted red clay had slight expansion deformation under the infiltration of Cr（VI）,Zn（II）and distilled water.When the Cr（VI）concentration increased from0 to 0.1M,the swelling strain of red clay increased from 3.0%to 3.7%,and the saturated permeability coefficient decreased from 2.94×10^-7 cm/s to1.55×10^-7 cm/s.（2）Through suction controlled drying shrinkage tests,the influence of chemo-osmotic coupling on the deformation characteristics of heavy metal contaminated clay under unsaturated conditions was studied.The results showed that when the Cr（VI）concentration increased from 0 to0.1M,the void ratio of red clay decreased from 0.832,0.831,0.830 to 0.809,0.805,0.804 under suction of 2 MPa,4.2 MPa,and 38 MPa,respectively.The higher the Cr（VI）concentration was,the greater the controlled suction was,the greater the shrinkage rate and deformation of red clay were,and the smaller the shrinkage void ratio was.When the suction reached 2 MPa,the increase of suction had little effect on the shrinkage void ratio.（3）Through oedometer tests,deformation characteristics of heavy metal contaminated clay under chemo-hydro-mechanical conditions were studied.The results show that consolidation coefficient and permeability coefficient of saturated Cr（VI）contaminated clay decreased,volume compression coefficient increased first and then decreased with the increase of vertical stress.With the increase of Cr（VI）concentration,rebound index of red clay increased,while compression index and yield stress decreased.With the increase of soil suction,yield stress increased,while rebound index and compression index decreased.（4）Through mercury injection tests and electron microscope scanning tests,the microstructure evolution characteristics of heavy metal contaminated clay under chemo-hydro conditions were studied.The results show that the compacted red clay had an obvious double pore structure,and Cr（VI）and soil suction mainly affected macropores.The higher the Cr（VI）concentration was,the larger the void size of macropores was,and the smaller the cumulative void ratio of macropores in saturated state.When the soil reached unsaturated state,the void size of macropores decreased with the increase of Cr（VI）concentration.