Experimental study on microcosmic characteristics of organic polluted formations encountered by direct push drilling
Direct push drilling technology has the advantages of no flushing medium,fast speed,small disturbance,etc.,but it is susceptible to the interference of factors such as large differences in the engineering properties of the soil at the site of organic contamination,resulting in tilting of the borehole and other phenomena.Organic pollutants will change the microstructure of the soil,resulting in changes in soil engineering properties,which in turn reduces the accuracy of direct drilling sampling points.Typical organic pollutants toluene and perchloroethylene were selected,and soil samples with different pollutant concentrations(toluene:75,120 and 672 mg/kg;perchloroethylene:11,53 and 183 mg/kg)were prepared to simulate the drilling encountered with the organically contaminated stratum.XRD,SEM,contact angle and nitrogen adsorption and desorption tests were carried out to investigate the changing rules of microstructure of the soil samples under the influence of different organic pollutant concentrations.The results of the SEM image analysis and nitrogen adsorption and desorption tests showed that:toluene and perchloroethylene encapsulated and chemically damaged soil samples,resulting in the agglomeration of soil particles,the reduction of the specific surface area,the obvious increase in the number of small pores,and the decrease in the pore volume of soil;the content of clay particles was 30.28%at the highest level.The highest clay content of 30.28%in soil sample 2#after 672mg/kg toluene and 183mg/kg tetrachloroethylene contamination,the specific surface area decreased by 30.70%and 33.40%,respectively,and the Pearson's correlation coefficient of r=0.382 indicates that there is a certain positive correlation between the content of clay particles and the rate of reduction of the specific surface area.Meanwhile,due to the wrapping effect of non-polar molecules toluene and perchloroethylene on the soil particles,the hydrophilic groups of the soil samples were isolated,resulting in the deterioration of the hydrophilicity of the soil samples and the increase of the contact angle.This study suggests that organic pollutants can lead to changes in the microscopic characteristics of the soil,which ultimately leads to an increase in the non-homogeneity of the organically contaminated strata,which in turn can have an impact on the direct push drilling trajectory.
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