Experimental And Theoretical Research Of Influence On Electrical Resistivity Of Soil-Cement By Pollution

Pollution can bring the strength depression of soil-cement foundation and induce instability or disruption of building,so studying the influence on soil-cement by pollution has become more and more important which made it a new topic on the area of environmental geotechnical engineering.But at present,there are no special means and methods for polluted soil-cement testing in domestic or foreign.In this paper,a series of lab tests were conducted to study both the environmental pollution influence and soil pollution influence on soil-cement.The soil-cement samples were soaked in H₂SO₄,NaOH solution to simulate the enviromental pollution,and the soil-cement samples were made by the soil contaminated by H₂SO₄,NaOH,MgCl₂,MgSO₄,Na₂SO₄ to simulate the soil pollution.Utilized the automatic tester for electrical resistivity of soil-cement developed by author personally,the characteristic of electrical resistivity of soil-cement under environmental pollution and soil pollution were studied and the variety laws of electrical resistivity changed with infectant component, concentration(or content),age and unconfined compression strength were pointed out.The main achievements are as followed:Firstly,the limitation of electrical model of soil-cement(Komine model) was pointed out and a new electrical model of soil-cement was proposed, based on detailed study of Komine model and observation analysis of soil-cement'SEM photos.Secondly,as a special electrochemical system,electrochemical effect problems such as polarization of direct current should be considered during test.On a basis of test and former's experience,the test method of electrical resistivity suitable for polluted soil-cement was brought forward and an automatic tester for electrical resistivity testing was developed to achieve the test process intelligentize,which was granted invention patent.Thirdly,the characteristic of electrical resistivity of soil-cement under environmental pollution was studied by the numbers.(1)Soaked in H₂SO₄ solution:both the electrical resistivity of soil-cement and the electrical resistivity of pore water were increased with the increment of age and decreased with the increment of solution concentration;the formation factor was increased with the increment of age and solution concentration;the unconfined compression strength of soil-cement was increased with the increment of electrical resistivity of soil-cement.And an anticipating formula of electrical resistivity of soil-cement was drawn out.After considered the factors of erosion,the Archie law was modified and the model of electrical resistivity of soil-cement under H₂SO₄ erosion was established.Meanwhile, the electrical resistivity of soil-cement was used as a quantization index to evaluate the degree of soil-cement eroded by H₂SO₄ solution.(2)Soaked in NaOH solution:the electrical resistivity and the unconfined compression strength of soil-cement and electrical resistivity of pore water followed the same way as the soil-cement soaked in H₂SO₄ solution;the formation factor was decreased with the increment of age,whereas was increased with the increment of solution concentration.An anticipating formula of electrical resistivity of soil-cement under this condition was drawn out,too.Fourthly,the characteristic of electrical resistivity of soil-cement under soil pollution was studied.The electrical resistivities of soil-cement contained contaminated soil such as H₂SO₄,MgSO₄,and Na₂SO₄ were increased with the increment of age,and firstly increased and then decreased with the increment of pollutant content.And that of soil-cement contained NaOH contaminated soil was increased with the increment of age and pollutant content.While that of soil-cement contained MgCl₂ contaminated soil was increased with the increment of age and decreased with the increment of pollutant content;an anticipating formula of electrical resistivity of soil-cement contained MgCl₂ contaminated soil was drawn out. All the unconfined compression strength of soil-cement contained these contaminated soil list above were increased with the increment of electrical resistivity of soil-cement.Fifthly,based on the comparison of unconfined compression strengths before and after polluting,an influence coefficient formula of soil-cement strength was set up on the basis of pollutant concentration(or content) which can modify the formula 11.2.4-2 in《Technical code for construction ground improvement》.According to the acidity and alkaline of contamination component,not only the environmental pollution but also the soil pollution can be divided into three conditions:acidity condition (represented by H₂SO₄),alkali condition(represented by NaOH)and neutral condition(represented by MgCl₂,MgSO₄,Na₂SO₄).For above given pollution conditions,the strength value can be calculated easily by respective relation between electrical resistivity and strength if the electrical resistivity of soil-cement was measured,in turn the single pile's capacity which was determined by the material strength of made-up piles can be calculated based on the electrical resistivity of soil-cement.Sixthly,the variety of electrical resistivity of soil-cement with age, pollution concentration(or content)and unconfined compression strength is aroused by the variety of pore structure and the quantity of electric ion.With the increment of electrical resistivity of soil-cement,the whole structural conductibility became lower,the connection between soil particles became tighter,the void ratio became smaller and the pore connectivity became worse.All of those resulted in an increment of compressive strength of soil-cement.Seventhly,the compression-destroying process of soil-cement is a damage process in practice.The electrical resistivity of soil-cement can reflect the law of soil-cement strength variety commendably.On the basis of electrical resistivity variety under compression process,the damage-evolvement equation was obtained and a damage model of soil-cement was established primarily based on the strain of soil-cement and current variety.