煤矸石改良膨胀土特性及其最佳掺量条件下的孔隙结构表征

为减小膨胀土对土木工程设施及农业生态环境的危害,进行掺加煤矸石粉改良膨胀土的试验研究。该文以内蒙古兴和县高庙子乡的膨胀土和煤矸石为研究对象,通过无荷膨胀试验、有荷膨胀试验和收缩试验确定煤矸石粉的最佳掺量,对最佳煤矸石粉掺量的膨胀土进行干湿循环试验,利用直剪试验测定每次干湿循环后试件的抗剪强度指标;通过压汞试验测得孔隙特征值,从微观角度揭示强度变化机理。试验结果表明:煤矸石粉掺量为6%时抑制膨胀土的胀缩性效果最佳;干湿循环作用使素膨胀土黏聚力和内摩擦角均有所衰减,掺入煤矸石粉后强度衰减得到控制;随干湿循环次数的增加孔径逐渐向大孔范围聚集,团粒结构增多,使素膨胀土的抗剪强度指标降低;经过5次干湿循环,掺加煤矸石粉土样的大孔孔隙密度比素膨胀土降低约35%,煤矸石有效阻止膨胀土的强度劣化。

Strength properties of solidified expansive soil with coal gangue and its pore structure characterization under condition of optimum dosage

Expansive soil is a kind of clay with high plasticity and sensitivity. It has strong characteristics of water-absorbing expansion and water-losing contraction, so its strength is easily affected by dry and wet circulation. Under the condition of dry-wet cycle, expansive soil tends to show certain softening characteristics, and its deformation resistance and strength will gradually decline, which will easily lead to the instability of slope, subsidence of roadbed, damage of irrigation and water conservancy facilities, aggravation of soil erosion, and impact on the agricultural ecological environment. In order to weaken damages to civil engineering facilities and ecological environment induced by expansive soils, the experimental study on the expansive soil mixed with coal gangue powder was carried out. The purpose of this paper was to study strength properties of solidified expansive soil with coal gangue powder and microscopic pore characteristics. Expansive soil and coal gangue used for testing were collected from Gao miaozi township, Xinghe county, Inner Mongolia, China. The combination of different ratios of coal gangue was used to treat expansive soil. The optimum dosage of coal gangue powder was determined according to the no-load swelling test, the loaded swelling test, and the contraction test. And then, we conducted the drying and wetting cycle test on expansive soil with the optimum dosage of coal gangue. In addition, the index of shear strength, including cohesion and internal friction angle, obtained from the shear strength test, and pore characteristic values, consisting of porosity, total pore volume, cumulative pore volume and pore density, achieved from the mercury intrusion test. We revealed the strength change mechanism in the view of microcosmic level. The test results showed that the expansion and contraction decreased after mixing coal gangue powder. The optimal dosage of coal gangue powder was 6%. Compared with unmixed soil sample, the no-load expansion rate, loaded expansion rate and shrinkage rate of improved soil sample were reduced by 7.7%, 36% and 40%, respectively. The dry-wet cycle reduced the cohesion and the angle of internal friction of expansive soil and decreases with the increase of dry-wet cycles. The cohesive force and the attenuation of internal friction angle of coal gangue powder soil were all smaller than that of plain expansive soil. While shear strength attenuation restrained by adding coal gangue powder. The pore density-aperture curves were bimodal distribution. With the increase of dry-wet cycle, pore diameters gathered to big pore of diameter, and granular structure emerged, which depressed the strength indexes. The pore density of big pore in samples with coal gangue powder decreased by about 35% compared with expansive soil without coal gangue, after the fifth dry-wet cycle. As the number of dry-wet cycle increased, the porosity and total pore volume increased, and the big pores also gradually increased. The expansive soil sample mixed with coal gangue powder restricts the formation of large pores, inhibits the damage of dry-wet cycle to the pore of expansive soil, and thus reduces the effect on the strength of expansive soil sample. In conclusion, coal gangue powder can prevent strength of expansive soil from reducing via restraining pores in samples.