Experimental And Theoretical Study Of Influence On Strength Of Soil-Cement Polluted By Sewage And Industrial Wastewater

Pollution can change the physical properties of soil, further may affect the strength of soil-cement foundation, in turn, induce instability or disruption of buildings. Therefore, studying the effect of pollution on soil-cement has become more and more important which made it a new topic in the area of environmental geotechnical engineering. In recent years, most researchers just considered one single chemical component made in the lab as the polluted medium, which is far from the real engineering condition. Based on this, the sewage and industrial wastewater taken from the real environment were considered as the medium in this study. Two types of soil-cement samples were made of either normal Portland cement or slag Portland cement:(1) use different concentration's sewage and industrial wastewater mixed with silty clay soil to form the contaminated soil, and then mixed with cement to form the soil-cement block to model the pollution of soil-cement with the soil polluted by groundwater; (2)After mixing the cement with the non-contaminated silty clay soil to form the soil-cement block, put the soil-cement blocks into the liquids with various concentraties of sewage or industrial wastewater to model the soil-cement column under the pollution of groundwater. Considering the difficulty of application of traditional method for the contaminated soil, the electrical resistivity method was introduced to investigate the soil-cement under different pollution types and conditions. The parameters studied in this study were included the unconfined compression strength, electrical resistivity, age, concentration, liquid and plastic limit indexes, transfer of contaminant, and damage and so on. The main achievements are as followed:Firstly, the law of liquid and plastic limit indexes of contaminated soil polluted by sewage and industrial wastewater with different concentration was studied. Also the change mechanism of contaminated soil based on the chemical compositions of polluted liquids was discussed.Secondly, as a special electrochemical system, electrochemical effect problems such as polarization of direct current should be considered during electrical resistivity measuring test. On a basis of test and previous experience, the method suitable for the synchronous testing electrical resistivity of soil-cement in uniaxial compression test was presented and a simplified device for electrical resistivity measuring was developed.Thirdly, the characteristic of strength and electrical resistivity of soil-cement under soil pollution was studied systematically. Under the same contamination concentration, no matter it was normal Portland cement sample or slag Portland cement sample, the unconfined compression strength and electrical resistivity were increased linearly with the increase of the logarithm of age; while under the same age, they were decreased exponentially with the increase of the contamination concentration.Fourthly, the characteristic of strength and electrical resistivity of soil-cement under soaking environment was studied systematically. Under the same contamination concentration, no matter it was normal Portland cement sample or slag Portland cement sample, the unconfined compression strength and electrical resistivity were increased linearly with the increase of the logarithm of age; while under the same age, they were decreased exponentially with the increase of the contamination concentration.Fifthly, in the above two pollution types, the unconfined compression strength of soil-cement had a linear correlation with electrical resistivity. This correlation may be used to predict and check the strength of soil-cement.Sixthly, a strength equation of soil-cement was proposed on the basis of the pollution concentration and age.Seventhly, under the analysis of three transferring types of contamination medium in soil-cement, the corresponding iron transferring model was built. By observing the microstructure images of soil-cement, the principle of pollution for soil-cement was revealed and the affection model diagram of pollution for soil-cement structure was found. Also the concept of erosive degree was presented and the erosive mathematical model of the contamination polluted soil-cement was built.Eighthly, the quantity equation of consumption of SO42- per volume was derived from the equation of SO42- erosive soil-cement.Nighthly, the modified coefficient of strength was proposed based on the strength testing date. And the statistic value of modified coefficient under different environmental conditions was obtained.Tenthly, according to the synchronous tested electrical resistivity in the unconfined compression strength test, using the ratio of effective current to the initial current during deformation to describe damage, the soil-cement damage model based on the current variation was built. This model with a simply form was no staged strain and unified all the strain range to a quartic polynomial equation independently with the types of cement and pollution.This study has a pronounced significance for understanding the erosive of sewage and industrial wastewater for the soil-cement composite foundation correctly, also gives a basis experiment date for the further research on the durability of soil-cement composite foundation. The application of the electrical resistivity method solvs the problem for the traditional method using in investigating erosive of contaminated soil and enlarges the application of electricity method using in the contaminated soil. This study also has a great practical significance and widely application prospects for the application of electrical resistivity method in the environment geotechnical engineering.