Experimental Study On Dynamic Characteristics Of Copper Contaminated Clay In Guangzhou And Foshan Area

With the rapid development of economic construction in the Pearl River Delta(PRD),ecological protection requires the rectification or relocation of some heavy polluting industries.In recent years,the problem of heavy metal pollution caused by the relocation of these sites has not been properly dealt with.According to the bulletin of national soil pollution survey,the pollution of heavy metals in the PRD exceeds the standard,especially the copper in Guangzhou,Foshan and other surrounding areas.Due to the long-term pollution in history and the late start of effective control measures,the horizontal and vertical infiltration of groundwater leads to the expansion of the pollution scope,which further increases the difficulty of control.In the process of economic construction,some infrastructure facilities which will produce dynamic load inevitably have to pass through the copper ion polluted areas,such as expressways,subways and so on.The mechanical particularity of copper ion polluted soil makes its dynamic characteristics under dynamic load very different from the general soil.If it is treated according to the general foundation soil in the process of relevant engineering design and construction,which can not be improved The research in this aspect will lay a hidden danger for the long-term operation of the project.In this paper,the unpolluted shallow soil in Guangzhou area is used to carry out relevant geotechnical tests to determine the basic parameters of soil samples.The dynamic triaxial tests under different cyclic dynamic stress ratio,effective confining pressure and load frequency are carried out by manually configuring soil samples with different concentrations of copper ion pollution.The development laws of cumulative axial strain,dynamic elastic modulus and cumulative dynamic pore pressure characteristics of soil samples before and after copper ion pollution are studied The research results are as follows:(1)The basic physical properties of the test soil are tested,and the natural density,moisture content,specific gravity,liquid plastic limit and other parameters of the soil sample are obtained.On this basis,the steps of soil sample configuration,production,saturation,consolidation and the corresponding operation basis are explained.(2)The critical cyclic dynamic stress ratio(CSR')and dynamic strength of soil samples are decreased with the increase of copper ion concentration.The critical state line between copper ion concentration and CSR'is obtained from the fitting relationship.The safety zone and failure zone of soil sample state are divided,which provides reference for the engineering design of copper ion pollution area.(3)The increase of copper ion concentration and effective confining pressure is more conducive to the development of the cumulative axial strain of soil samples,and the increase of load frequency has a certain limit on the development of cumulative axial strain,and the greater the concentration of copper ion pollution,the more obvious the limiting effect is.Based on the experimental data,an improved hyperbolic model of cumulative axial strain under the influence of copper ion concentration and cyclic dynamic stress ratio is established.The model fitting effect is better by comparing the predicted value of the model with the experimental value.(4)The initial dynamic elastic modulus(E_max)of stable soil sample decreases slightly with the increase of copper ion concentration,and increases obviously with the increase of effective confining pressure.However,with the test loading,the dynamic elastic modulus(E)of soil sample polluted by copper ion decays faster and reaches a lower stable value.The dynamic elastic modulus model under the influence of copper ion concentration and effective confining pressure is established.Through regression analysis,the fitting result of 1/E??linear model of dynamic elastic modulus is better than E??hyperbolic model.(5)The cumulative pore pressure of soil samples develops more rapidly and the limit pore pressure is higher with higher copper concentration,effective confining pressure and lower load frequency.The development of the normalized cumulative pore pressure ratio of the uncontaminated soil is not affected by the change of effective confining pressure,but the introduction of copper ions aggravates the effect.Therefore,the influence of effective confining pressure on the development of the dynamic pore pressure ratio of the soil samples polluted by copper ion should be considered.Based on the cumulative axial strain model,the cumulative dynamic pore pressure hyperbolic model of copper ion contaminated soil is established,and regression analysis model is established The relationship between the type parameters and the concentration of copper ion and effective confining pressure.(6)Through the physical and chemical reaction between copper ions and soil particles and its own charging characteristics,the microstructure of soil is changed,which makes the copper ion contaminated soil show different dynamic characteristics from the general soil.