直推钻进钻遇有机污染地层微观特征试验研究

Experimental study on microcosmic characteristics of organic polluted formations encountered by direct push drilling

摘要:

直推钻进技术具有无冲洗介质、速度快、扰动小等优点，但是易受到有机污染场地土体工程性质差异等因素干扰，造成钻孔倾斜等现象。有机污染物会改变土体微观结构，导致土体工程性质发生变化，进而降低直推钻进取样点位精度。选取典型的有机污染物甲苯和四氯乙烯，制备不同污染浓度（甲苯浓度：75、120和672 mg/kg；四氯乙烯浓度：11、53和183 mg/kg）的土样来模拟钻遇的有机污染地层。通过XRD、扫描电镜、接触角和低温氮气吸附脱附试验探究土样在不同有机污染物浓度影响下微观结构的变化规律。SEM图像分析与氮气吸附脱附试验结果表明：甲苯、四氯乙烯对土样的包裹作用和化学破坏作用会让土颗粒团聚、比表面积减小、小孔隙数量明显增多、土体孔体积减小；其中粘粒含量最高为30.28%的2号土样在受672 mg/kg甲苯和183 mg/kg四氯乙烯污染后比表面积分别减小了30.70%和33.40%，Pearson相关系数r=0.382说明粘粒含量与比表面积减小率存在一定的正相关性。由于非极性分子甲苯、四氯乙烯对土颗粒的包裹作用，隔绝了土样的亲水性基团，导致土样亲水性变差、接触角增大。本研究表明有机污染物会导致土体微观特征的改变，最终会导致有机污染地层非均质性增强，进而会对直推钻进轨迹产生影响。

关键词:有机污染物;土体微观结构;接触角试验;氮气吸脱附试验;直推钻进

Abstract:

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.

Key words:organic pollutant;soil microstructure;contact angle test;nitrogen adsorption desorption test;direct push drilling