Thermo-hydro-mechanical modeling of heterogeneous subsidence in desiccation-cracked clayey strata under soil-atmosphere interaction
Creators: name: Jabbarzadeh, Milad
Publisher: name: figshare
Year: 2024
Subjects: classificationCode: 400502
subject: Civil geotechnical engineering

description: Ground subsidence refers to the gradual downward movement of the ground’s surface, often occurring on a large scale due to excessive extraction from aquifers. Nowadays, climatic changes and global warming are fundamental phenomena that can lead to the drying of surface layers of the soil. From a geomechanical and environmental geotechnics perspective, this phenomenon can pose risks such as cracking and increased intensity of ground subsidence. Ground subsidence in cracked soils does not occur uniformly. The rate of subsidence in cracked parts differs from that in uncracked parts. The presence of pathways for increased energy and moisture exchange between the soil and the atmosphere through crack walls causes this difference in ground displacement, leading to the creation of differential settlements that can pose risks to the stability of surface and underground structures. Therefore, the aim of this research is to numerically model the thermo-hydro-mechanical subsidence of heterogeneous layers of desiccation cracked clay soil under the influence of soil-atmosphere interaction. To achieve this, the geometry of cracked soil models, emphasizing width, depth, and spacing between cracks, was determined using statistical analysis of existing data from literature and field observations from Qom and Eshtehard plains in Qazvin. Subsequently, a coupled thermo-hydraulic model was developed to study the moisture and temperature changes in cracked soils under climatic conditions in Qom over a three-year period from 2015 to 2017. Additionally, a coupled hydro-mechanical model was established to investigate the impact of climatic changes on heterogeneous subsidence in cracked soil and homogeneous subsidence in intact soil. The theoretical framework of the numerical model includes governing equations for heat transfer (Fourier’s law), water and gas flow (generalized Darcy and Fick’s laws), and soil deformation (Barcelona Expansive Model, BExM). The results of the model showed that desiccation crack leads to significant changes in the thermal and moisture profiles of the soil. This is attributed to the formation of new channels with soil cracking and the exchange of energy and moisture through crack walls, altering the flow regime. Furthermore, deep cracks allow for moisture changes in higher depth of the soil, which can also affect heat transfer through soil moisture changes. In this study, a simplified approach was proposed to estimate soil temperature changes in the presence and absence of cracks in a specific depth of the soil. Interestingly, the findings indicated that cracked soil has approximately 1.4 times higher drying rate than intact soil. Additionally, the results showed that the presence of crack increases the vertical displacement range, including subsidence and swelling, sixfold. Moreover, the mechanism of swelling and shrinking displacement of cracked soil was determined, where the soil surface between two cracks exhibits a concave shape during swelling and a convex shape during shrinking.