Effects of clay content on the volumetric behavior of loess under heating-cooling cycles

Abstract

Although numerous studies have been carried out on investigating thermal volume changes in different soils, limited attention has been paid to loess. This study aims to investigate the effects of clay content on the deformation of loess under heating-cooling cycles. Three soils with different clay contents (i.e. SA: 7%; SB: 13%; SC: 35%) were prepared with loess collected in situ through the sedimentation method. The soil volume changes were measured under heating-cooling cycles by using a thermal invar oedometer. To interpret the experimental results, X-ray diffraction (XRD) and scanning electron microscope (SEM) tests were conducted to identify the composition and microstructure of tested soils, respectively. The results show that the plastic axial strains of SA, SB, and SC accumulate to a certain level with the increasing number of heating-cooling cycles. At the stable state, the plastic axial strain of SC is 264% and 52% larger than those of SA and SB, respectively. On the other hand, the linear thermal expansion coefficient of SC is 66% and 20% larger than those of SA and SB, respectively. As evidenced from the XRD test, the clay in loess mainly contains kaolinite, chlorite, and illite, while the composition of silt is dominated by quartz. The clay minerals are more sensitive to thermal fluctuations than quartz because of the electrical double layer. SC, whose clay content is deliberately enhanced, exhibits a larger plastic axial strain and linear thermal expansion coefficient than do SA and SB.

概要

目 的

• 1. 探讨加热-降温循环温度荷载下黄土中黏土矿物对其变形特性的影响, 包括累积塑性压缩变形和热膨胀系数.

• 2. 研究黄土由于施加温度荷载产生变形的微观机理.

创新点

• 1. 明确了对黄土由温度荷载引起累积塑性变形具有重要影响的矿物成分;

• 2. 研究得到黄土由于施加温度荷载产生变形的微观机理.

方 法

• 1. 通过溶液沉积法, 分离黄土中的黏土矿物, 并制备出三种不同黏土矿物含量的黄土测试样品;

• 2. 通过温控一维固结仪, 测试不同黏土矿物含量的黄土在循环温度荷载下的累积塑性变形和热膨胀系数;

• 3. 通过扫描电镜试验和矿物成分测试, 研究黄土由于施加温度荷载产生变形的微观机理.

结 论

• 1. 黄土中所含伊利石、绿泥石、高岭石和蒙脱石等黏土矿物对其由于施加温度荷载所产生的累积塑性变形具有重要影响;

• 2. 黄土孔隙比对其由温度荷载引起的累积塑性变形和热膨胀系数影响较小.