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publications

Role of substrate roughness in soil desiccation cracking

Published in Canadian Geotechnical Journal, 2024

Soil desiccation crack is ubiquitous in nature, yet the physics of its initiation and propagation remain under debate, as it involves complex interactions across multiple fields of mechanics, hydraulics, and thermals. Here, an experimental attempt is made to uncover the role of substrate roughness on the soil desiccation process. The substrate roughness is deliberately fabricated by 3D printing, whereas the thickness of sample and environmental humidity are controlled to eliminate the effect of large hydraulic gradient. Four types of soils with varying expansibilities were desiccated on substrates with varying roughness. It reveals that: (1) soil desiccation crack evolution can be conceived as a competing process between the shear failure of soil-substrate interface, i.e., slippage of interface, and the tensile failure of soil, i.e., crack initiation, in minimizing the total energy of drying soil; (2) substrate roughness alters the failure mode and shear strength of soil-substrate interface and its sensitivity to moisture, thereby it regulates the pattern of how soil crack propagates upon drying; (3) soil expansibility is recognized as a key factor governing the crack-initiation point in addition to the widely recognized air-entry, and flaws in soil are the sources for the 120° crack angle and bimodal crack angle distribution.

Recommended citation: Yang, Y., Zhang, C., Gou, L., Chen, R., & Dong, Y. (2024). Role of substrate roughness in soil desiccation cracking. _Canadian Geotechnical Journal_, 61(12), 2686-2703.
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Nucleation-percolation transition in desiccation cracking of clay

Published in Physical Review E, 2025

Crack formation plays a critical role in both natural and engineered materials, influencing the structural integrity and failure of materials from soils to buildings. In this study, the clay desiccation cracking is observed to exhibit a transition of cracking mode from nucleation through avalanche to percolation. This cracking mode transition is dictated by the strain field disorder, which is deliberately regulated by changing the pore structure heterogeneity, with nucleation dominating at low disorder and percolation emerging at higher disorder levels. These transitions are captured by the fractal dimension of the sample-spanning crack, with ~0.99 for nucleation, ~1.72 for percolation, and values in between for avalanche, maintaining universality among the four types of clay. Additionally, the fractal dimension increases with strain field disorder in avalanche mode, which can be well captured by a logarithmic relation derived via the fractal tree model. Moreover, this logarithmic relation is universal among both the experimental data of the four types of clay and the numerical data of the classical fuse model. Our findings enhance the understanding of how material heterogeneity governs crack propagation, providing valuable insights for predicting and controlling fractures in natural and industrial processes.

Recommended citation: Yang, Y., Zhang, C., Kim, H., & Chen, R. (2025). Nucleation-percolation transition in desiccation cracking of clay. _Physical Review E_, 111(5), L053501.
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Measuring fracture toughness of clayey soils in a wide suction range

Published in Géotechnique, 2026

Fracture toughness is a fundamental variable in describing cracking behaviour, yet it remains challenging to measure for clayey soils partly due to its extremely high dependence on water content or suction. Herein, a novel expansion ring method is proposed for measuring the fracture toughness of clayey soils in a wide suction range from below the air-entry value to several hundred megapascals. This method utilises an expanding ring mechanism to generate outward pressure on the inner boundary of thin concentric clay samples. This set-up exhibits two features: approximately zero gravitational stress in samples; and no stress concentration around loading points. These features enable mode I crack nucleation in very soft, even saturated clay samples. Thereafter, the strain variations around the crack tip are captured using digital image correlation, facilitating the calculation of the critical J-integral at the crack initiation point (J_Ic), which is a measure of fracture toughness. The applicability of the proposed method is tested using three types of clayey soils representing a wide range from non-expansive to highly expansive. The validity of the method is assessed through the existence of the J-dominated zone and the path independence of the _J-integral. Moreover, the repeatability of the method is validated through independent trials. Results reveal that JIc can vary non-monotonically with suction, reaching maximum values of 1·56 J/m2, 3·55 J/m2 and 6·26 J/m2 for bentonite, HN clay and kaolinite, respectively.

Recommended citation: Yang, Y., & Zhang, C. (2026). Measuring fracture toughness of clayey soils in a wide suction range. _Géotechnique_, 1-15.
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Suction and Volume Evolutions of Clayey Soils upon High-Stress Unloading and Subsequent Soaking

Published in Canadian Geotechnical Journal, 2026

Deep excavations may fail after rainfall because high-stress unloading can create an unsaturated state with appreciable suction, and subsequent wetting may trigger either swelling or collapse depending on soil type and stress path. Herein, a series of high-stress oedometer tests was conducted to investigate the evolutions of suction, volume, K0 coefficient, and small-strain shear modulus. Two clayey soils were employed: nonexpansive kaolinite and expansive clay. Samples were tested under three loading–1st unloading–soaking–2nd unloading stress paths, covering two maximum vertical stresses (1.6 and 3.2 MPa) and two unloading ratios at soaking (0.25 and 0.50). Results show: (1) unloading-induced suction increments up to 408 kPa (kaolinite) and 610 kPa (expansive clay) as vertical stress decreases from 3.2 MPa to ~5 kPa under K0 condition; suction change increases linearly with the logarithm of the vertical-stress change. (2) During soaking, volumetric changes reach 47.2% and 55.8% of the prior rebound for kaolinite and expansive clay, while K0 and small-strain shear modulus vary by <3%. (3) An effective stress-based model is proposed for the volume evolution upon high-stress unloading and subsequent soaking, incorporating the effect of unloading-induced suction. This model effectively captures the volume change in the unloading and soaking stages with R2 ≥ 0.86.

Recommended citation: Yang, Y., Zhang, C., Liu, Z., Yuan, J., & Chen, R. (2026). Suction and Volume Evolutions of Clayey Soils upon High-Stress Unloading and Subsequent Soaking. _Canadian Geotechnical Journal_, (ja).
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teaching

Teaching experience 1

Undergraduate course, University 1, Department, 2014

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Teaching experience 2

Workshop, University 1, Department, 2015

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Yuhan Yang