Analysis of the Mechanical Properties and Mechanism of Zinc Ion‐Contaminated Red Clay

Abstract

To study the effects of different concentrations of zinc ions on the mechanical strength, material composition, and microstructure of red clay, a triaxial test, an x-ray diffraction test, an x-ray fluorescence spectrometry test, a scanning electron microscopy test, and a mercury intrusion test were carried out on contaminated soil to investigate the mechanisms of zinc ion-contaminated red clay. The results show that the higher the concentration of zinc ions, the smaller the shear strength and cohesion of the red clay. The internal friction angle is increased first and then decreased. From material composition, zinc ion makes montmorillonite and hemite disappear in red clay. With the increase of zinc ion concentration, quartz semiquantitative increase and kaolinite semiquantitative decrease and the content of SiO2, Fe2O3, and Na2O reduces. Microscopically, the structure of red clay changes from floc structure to granular and aggregate structure after the zinc ions are added, while the contact of the particles is converted to point contact. With the increase of the concentration of zinc ions, the porosity and the fractal dimension of the red clay gradually increase, and the stability of the granular structure is weakened.

Influence of Soil Particle Size on the Engineering Properties and Microstructure of a Red Clay

“…The soil sample with a diameter of 5.00 mm was mainly composed of cracks, pores, and edge cracks. When the dry density increased to 1.4 g/cm 3 , the cracks in the middle of the soil sample decreased, and the independent pores decreased when the dry density reached 1.5 g/cm 3 . With the same dry density, the larger the particle size of the red clay, the greater the number of independent pores, but the cracks in the soil sample with the smallest particle size of 0.25 mm were the most developed.…”

“…In Figure 9, at the same dry density, the UCS is most prominent at a particle size of 0.25 mm, smallest at a particle size of 2.0 mm, and closest at particle sizes of 0.5 mm, and 5 mm. The average UCS is 87.46 kPa for different particle sizes at a dry density of 1.3 g/cm 3 , increasing by 64.17% and 140.59% for dry densities of 1.4 g/cm 3 and 1.5 g/cm 3 , respectively. In Figure 10, the average UCS for different dry densities is 107.22 kPa at a particle size of 2.0 mm, increasing by 68.53%, 40.03%, and 40.42% at particle sizes of 0.25 mm, 0.5 mm, and 5.0 mm, respectively.…”

“…Three soil samples with different particle sizes were selected, and their masses were 163.21 g, 175.77 g, and 188.32 g, respectively. The three samples were compacted in six layers, obtaining cylindrical samples with dry densities of 1.3 g/cm 3 , 1.4 g/cm 3 , and 1.5 g/cm 3 . Finally, an UCS test was carried out using an unconfined compression apparatus.…”

“…Next, three soil samples with different particle sizes with 102.01 g, 109.86 g, and 117.70 g were selected. We compressed soil samples of different masses into a 20 mm ring knife to obtain samples with dry densities of 1.3 g/cm 3 , 1.4 g/cm 3 , and 1.5 g/cm 3 , respectively. WD cycles were performed after saturation: the sample was placed in a constant temperature box at 40 • C for 12 h for drying cycles and then immersed in water with a saturator for 12 h for wetting cycles.…”

“…Red clay is a shared, but problematic soil characterized by a high liquid limit (LL) and plasticity index (PI) and usually presents a high natural moisture content (NMC). It is generally distributed in the hot and humid regions of South China [1][2][3]. With the development of the economy, an increasing number of railways and roads pass through this particular soil area.…”