Study on Hygroscopic Swelling and Dehumidification Cracking Characteristics of Expansive Soil under Acid Rain and Cyclic Drying‐Wetting

Abstract

In this study, to reveal the swelling and cracking characteristics of expansive soil subjected to cyclic drying-wetting of acid rain, the effects of acid rain and cyclic drying-wetting on the swelling deformation of expansive soil were studied by using the load-free swelling rate test. Afterward, a high-definition digital camera was used to capture the crack development images of the sample during the dehumidification process under cyclic drying-wetting of acid rain. Furthermore, the changes of the microstructure and mineral composition of the expansive soil after cyclic drying-wetting of acid rain were analyzed by using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. Finally, the effect mechanisms of acid rain and cyclic drying-wetting on the swelling deformation and crack development of the expansive soil were discussed. The results indicate that acid rain has a positive effect on the swelling deformation and crack development of the expansive soil. The effect is greater with a stronger acidity of rainfall. Moreover, the combined action of acid rain and cyclic drying-wetting can promote the swelling deformation and crack development of the sample more notably. The swelling rate of the sample increased most significantly during the first two-time cyclic drying-wetting. The measured swelling rates at pH = 3 and 5 are 23.7% and 20.6%, respectively, which are higher than the swelling rates of 19.0% at pH = 7. The humidity of samples is 17–18% after the first-time drying-wetting cycle. The crack area ratios (Mf) of the samples with pH values of 5 and 3 are, respectively, increased by 11.0% and 69.1%; the average crack width of the sample increases by 32.3% and 93.3%, respectively, compared with pH values of 7. After the fourth-time drying-wetting cycle, Mf and the average crack width of the samples under the rainwater environment of three pH values increase greatly, but the difference of Mf among them became unapparent. In addition, the microscopic test results show that acid rain can corrode the binding materials (e.g., SiO2, Al2O3, K2O, MgO, and CaO) in the expansive soil. The erosion of the binding minerals weakens the structural connection strength, resulting in continuous increases in both size and number of microvoids. Under the superimposed influence of cyclic drying-wetting, the above changes are even more dramatic. Macroscopically, the swelling deformation of expansive soil increases and the cracks develop rapidly.

Experimental and Numerical Simulation Study of Water Infiltration Impact on Soil-Pile Interaction in Expansive Soil

“…Although hygroscopic swelling is an essential attribute of expansive soil, it is worth noting that many other materials, such as paper, cotton, wood, nylon, sugar, and a range of other materials, are also hygroscopic. Some studies have examined and modelled the hygroscopic swelling behavior of rice and other materials [32][33][34][35][36]. As the hygroscopic swelling induces deformations on the free boundaries while increasing compression inside the model domain, it is suitable for simulating soil swelling behavior and the subsequent ground heave.…”

The Effect of Pore Solution on the Hysteretic Curve of Expansive Soil under Cyclic Loading

“…Studds et al [6] studied the swelling behaviour and water conductivity of bentonite in distilled water and salt solutions of different concentrations and obtained the characteristics of bentonite in dilute and strong solutions and a model that can predict its components and permeability. Chang et al [7] conducted a no-charge expansion rate test on expansive soil in an acid rain environment to study the deformation characteristics of the expansive soil in this environment and analysed the changes in the microstructure and mineral composition of the expansive soil after the drying and wetting cycle of acid rain by SEM as well as XRD.…”