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The effect of desiccation cracks on water infiltration in landfill cover under extreme climate scenarios
(2025-04-01)
Apriyono, Arwan
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Yuliana, Yuliana
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Kamchoom, Viroon
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Leung, Anthony Kwan
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Jotisankasa, Apiniti
Predicting water infiltration in clay poses a significant challenge, primarily due to the presence of desiccation cracks, which are amplified by extreme climate. Accurate methods for calculating water infiltration, considering crack variations under extreme climates are essential especially for landfill covers. The objective of this study is to explore the relationship between crack intensity factor (CIF) and water infiltration in high-plasticity clay, focusing on seasonal changes and extreme climate conditions. A series of double-ring infiltration tests was conducted in the field to observe the impact of desiccation cracks on water infiltration. Subsequently, a modified Green–Ampt method incorporating CIF was developed and validated against these field test results to improve water infiltration predictions. This study revealed that the maximum CIF was notably higher in the second dry season (11.4 %) than that in the first one (8.1 %), indicating soil structural degradation. An exponential correlation was observed between increased CIF and infiltration rates, attributed to cracks creating preferential pathways. In extreme climate scenarios, CIF increases could surpass 15 %, potentially elevating soil's saturated hydraulic conductivity (K<inf>s</inf>) by over 85 % relative to current climate conditions.
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Modelling root decomposition effects on root reinforcement and slope stability
(2025-03-01)
Phan, Trung Nghia
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Leung, Anthony Kwan
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Nguyen, Thanh Son
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Kamchoom, Viroon
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Likitlersuang, Suched
This study investigates the influences of root decomposition of two vetiver species on mechanical root shear reinforcement and vegetated slope stability. The transient variations of maximum root shear reinforcement (C<inf>r,max</inf>) of vetiver species was examined by combining the extended Root Bundle Model with the modified Wu's model. Existing laboratory data of the biomechanical properties (i.e., tensile strength, secant modulus) and morphological traits (i.e., diameter distribution, root length, orientation) of the decomposing roots following herbicide application were used as input parameters in the root reinforcement models to predict the root shear reinforcement. The predicted C<inf>r,max</inf> was then used in the slope stability analysis on the basis of Morgenstern-Price method to evaluate the temporal variation in the stability of vegetated slope with different slope angles and plant killing patterns. The combined model was capable of predicting the exponential reductions in C<inf>r,max</inf> following the transient declines in the root strength, secant modulus and diameter. The large variability in the tensile strength of decomposing roots could also be well captured through the use of Weibull survival function. The slope stability analysis highlighted that the vetiver roots contributed the most to the stability of slope when the slope angle was less than 45°. Additionally, it is recommended to refrain from killing the plants grown near the slope's toe, because this region is particularly susceptible to shallow slope failure.
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Effect of root water uptake on road movement across seasonal changes
(2025-01-01)
Yuliana, Yuliana
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Apriyono, Arwan
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Leung, Anthony Kwan
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Keawsawasvong, Suraparb
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Kamchoom, Viroon
The use of trees as roadside barriers provides benefits like noise and pollution control. On the other hand, the root systems can disrupt soil moisture, leading to uneven subsidence and impacting nearby structures. Knowing the appropriate distance between trees and pavement will allow for maximizing the plant's favourable impact on infrastructure. This study aimed to determine the safe distance between trees and pavement by examining the effects of transpiration on pore water pressure (PWP) and pavement subsidence under seasonal variations. The root water uptake was simplified in a finite element model using multiple hydraulic head boundaries and validated through field observations. A hypoplastic model was employed to simulate the non-linear behaviour and plastic strain accumulation in unsaturated soil. The findings indicate that the summer season exhibited a more noticeable change in negative PWP. Trees significantly reduce PWP, especially during summer seasons, creating higher suction near them due to evapotranspiration. Additionally, pavement edges closest to trees experience the most pronounced subsidence, likely due to a greater soil moisture deficit. Seasonal variations influence subsidence, with drier periods leading to more severe effects. Furthermore, the pavement with the distance 4 meters from the tree highlights a potential risk exceeded the cracking moment at 5<sup>th</sup> summer period, indicating a high risk of damage.
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The effects of desiccation crack and seasonal variation on hydrological response of compact clay embankment
(2025-01-01)
Apriyono, Arwan
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Yuliana, Yuliana
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Kamchoom, Viroon
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Leung, Anthony Kwan
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Jotisankasa, Apiniti
The presence of cracks significantly impacts the hydrological behaviour of clay embankments. This study aimed to enhance understanding of the complex interplay between the amount and propagation of desiccation cracks and seasonal variations. A full-scale embankment was constructed and equipped with an array of instruments, including pore water pressure, volumetric water content (VWC), and crack observer. The results suggested that continues cracks at shallow depths (0.5 m) exhibit significant seasonal fluctuations due to pronounced soil–atmosphere interactions, facilitating rapid water movement and substantial changes in crack width. In contrast, discontinuous cracks at intermediate depths (0.5 m) are less affected by seasonal changes, but they can propagate and connect over time due to repeated wetting and drying cycles. The crack intensity factor (CIF) above 0.4 m is highly sensitive to climatic variations, leading to pronounced fluctuations with changes in rainfall and dry conditions. The twofold increase in CIF values leads to a significant reduction in VWC (by 13.5%) at the depth of 0.25 m under the same atmospheric water balance. However, this effect is less pronounced at greater depths, such as 0.5 m, as discontinuous cracks are less effective in facilitating rapid drainage and moisture loss.
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Hydromechanical behaviour of a slope reinforced by grass roots under rainfall conditions
(2024-12-01)
Prasetyaningtiyas, Gayuh Aji
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Kamchoom, Viroon
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Leung, Anthony Kwan
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Likitlersuang, Suched
Soil bioengineering using vegetation has been considered an environmentally friendly solution to improve slope stability. Although several studies have demonstrated the contribution of vegetation to slope stability, a gap in understanding the mechanisms of grass root–soil interactions under rainfall conditions remains. This study investigates the effects of the roots of vetiver grass (Chrysopogon zizanioides) on the hydromechanical behaviour of an unsaturated soil slope using the centrifuge modelling technique. The changes in pore water pressure and slope deformation were monitored during the test. The monitored data were subsequently back-analysed and interpreted using seepage–stability analyses. In addition, this study focused on evaluating the effect of roots on slope stability, considering safety and pore water pressure during rainfall. Results revealed that the vetiver roots remarkably affected the initial suction of the slope by increasing the soil's air-entry value. The increased suction and the additional cohesion provided by the roots enhanced slope stability under rainfall conditions.
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Influence of biochar on the water permeability of compacted clay subjected to freezing–thawing cycles
(2024-06-01)
Chen, Zhongkui
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Kamchoom, Viroon
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Leung, Anthony Kwan
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Xue, Jiaxiang
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Chen, Rui
Seasonal variation of soil surface temperature, such as freezing and thawing, can induce increases in the water permeability in clay by mobilizing clay pore structure. This kind of weather-induced change in clay behavior may worsen the water-sealing performance during the construction and after closure operation of engineered structures such as soil barriers for tailings or man-made slopes. There is limited knowledge towards the influence of freezing–thawing cycles on clay microstructure and saturated permeability (K<inf>sat</inf>). This study investigated the saturated permeability of clay under freezing–thawing cycles and explored the uses of biochar as eco-friendly amendment to manipulate the permeability of compacted clay. Clay specimens were compacted with different initial water contents (30%, 34%, and 38%). The biochar application rates of 0%, 2%, 4%, 8% (by dry weight) were applied to measure their effects on the permeability of clay specimens. Saturated permeability was measured by the falling head tests. Any variation of biochar amended clay microstructure after freezing–thawing cycles was captured by the scanning electron microscope. The K<inf>sat</inf> was reduced by about one order of magnitude when the biochar application rate was larger than 4%. This may be attributed to the increase in the filling of the biochar particles in the clay intra-aggregate pores upon the transport of liquid water during the repeated freezing–thawing processes. The biochar may thus be recommended to minimize the K<inf>sat</inf> of geo-environmental structures in cold regions when sufficiently large application rate was used to facilitate the pore-filling process.
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Spatiotemporal variations of sand hydraulic conductivity by microbial application methods
(2024-01-01)
Kamchoom, Viroon
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Khattiwong, Thiti
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Treebupachatsakul, Treesukon
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Keawsawasvong, Suraparb
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Leung, Anthony Kwan
The spatiotemporal distributions of microbes in soil by different methods could affect the efficacy of the microbes to reduce the soil hydraulic conductivity. In this study, the specimens of bio-mediated sands were prepared using three different methods, i.e. injecting, mixing, and pouring a given microbial solution onto compacted sand specimens. The hydraulic conductivity was measured by constant-head tests, while any soil microstructural changes due to addition of the microbes were observed by scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) tests. The amount of dextran concentration produced by microbes in each type of specimen was quantified by a refractometer. Results show that dextran production increased exponentially after 5–7 d of microbial settling with the supply of culture medium. The injection and mixing methods resulted in a similar amount and uniform distribution of dextran in the specimens. The pouring method, however, produced a nonuniform distribution, with a higher concentration near the specimen surface. As the supply of culture medium discontinued, the dextran content near the surface produced by the pouring method decreased dramatically due to high competition for nutrients with foreign colonies. Average dextran concentration was negatively and correlated with hydraulic conductivity of bio-mediated soils exponentially, due to the clogging of large soil pores by dextran. The hydraulic conductivity of the injection and mixing cases did not change significantly when the supply of culture medium was absent.
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Dynamic changes in cellulose content and biomechanical properties of mycorrhizal roots during growth and decay
(2023-09-01)
Kamchoom, Viroon
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Chen, Xun Wen
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Leung, Anthony Kwan
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Sakolpanya, Tapakorn
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Srinil, Chortham
Aims: Arbuscular mycorrhizal (AM) fungi have been found to increase plant biomass, cellulose content, and the associated root biomechanical properties, but little is known about how AM fungi affect the in situ root decay process in terms of the changes in the chemical and biomechanical properties. Methods: In this study, we inoculated AM fungi to Bermuda grass (Cynodon dactylon L.) and measured the biomass, the contents of cellulose and lignin, and the biomechanical properties, including tensile strength and Young’s modulus of the grass roots as they grew for 180 days and then decayed for 360 days after burning or for 60 days after the herbicide application. Results: Results show that the AM fungi accelerated the accumulation of grass biomass and root cellulose content compared with non-mycorrhizal grass during the growth period. This effect of AM fungi made mycorrhizal grass generally maintained more biomass and cellulose content than non-mycorrhizal grass at every decaying stage. Inoculation of the AM fungi did not significantly change the root tensile strength or Young’s modulus, but it altered the correlations between tensile strength and root diameter, and Young’s modulus and root diameter. Mycorrhizal effects during the root decaying process appeared to diminish under herbicide treatment, compared with normal growth and burning treatments. Conclusion: Our study highlights the important role of AM fungi in maintaining in situ root biomass (a proxy for carbon content) from decaying or decomposing.
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Changes in Pore-Size Distribution and Hydraulic Conductivity of Compacted Soils by Grass-Derived Hydrochar
(2023-09-01)
Dong, Huan
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Leung, Anthony Kwan
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Chen, Rui
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Lourenco, Sergio
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Kamchoom, Viroon
Hydrochar is a biomass-derived carbon-rich material produced by the hydrothermal carbonization process which requires less energy than the pyrolysis production of biochar. The effectiveness of using hydrochar to amend soil properties, especially hydraulic conductivity, and the underlying mechanism that hydrochar follow remain unknown. This study measured the effects of grass feedstock and grass-derived hydrochar produced at two temperatures (180°C and 240°C) on the pore size distributions (PSDs) and saturated hydraulic conductivity (ks) of compacted silty-clay sand. Hydrochar affected the ks through predominantly the change of macropores of amended soil. Specifically, the addition of 180°C hydrochar [with a 60% specific gravity (GHs) of the soil] at the mass proportion (fH) of 2.5% evolved the PSD from unimodal to trimodal, creating a more open soil structure and increasing the ks by more than half an order of magnitude. When fH exceeded the threshold of 2.5%, the improvement of ks decreased in effectiveness following the compression of macropores. The 240°C hydrochar that has a larger GHs (than the 180°C case) has a high threshold of 5% and introduced a great increase in ks. Test results highlight the importance of avoiding adding excessive hydrochar to prevent the reduction of the effectiveness of drainage improvement.
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Reinforcement losses in soil stabilisation due to decomposing roots of Chrysopogon zizanioides and Chrysopogon nemoralis
(2023-02-28)
Phan, Trung Nghia
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Leung, Anthony Kwan
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Kamchoom, Viroon
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Likitlersuang, Suched
Quantifying evolutions of the biomechanical properties and mechanical root reinforcement to soil with the duration of root decomposition is important to land management strategy and to soil stabilisation purposes. However, the variations of these properties of the roots of herbaceous species, especially following herbicide application in agriculture practices, have rarely been studied. This study aims to measure the effects of root decomposition due to herbicide on the root biomechanical properties and root reinforcement provided by two contrasting vetiver species (Chrysopogon nemoralis and Chrysopogon zizanioides). We applied herbicide (i.e., propanil) to four treatments of each species, considering four different durations of decomposition (7-, 28-, 56- and 112-days since herbicide application). The biomechanical properties were measured by uniaxial tensile tests, whereas the root reinforcement to poorly graded sand (SP) was quantified by direct shear tests. Root decomposition significantly reduced mean root tensile strength, secant modulus and breakage strain of C. nemoralis and C. zizaniodes roots after 112 days since the herbicide application. Significant negative power correlations between root diameter and root strength (or root secant modulus) (R<sup>2</sup> = 0.39–0.86; p-value < 0.05) were identified. Root decomposition did not change the shape of these correlations, but they shifted downwards as roots decomposed. The root reinforcement also declined with the decomposition duration, in terms of root cohesion and maximum dilatancy within the study period. C. nemoralis displayed greater and quicker loss of both the root biomechanical properties and root reinforcement to soil than C. zizanioides.

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