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Modelling root decomposition effects on root reinforcement and slope stability
(2025-03-01)
Phan, Trung Nghia
;
Leung, Anthony Kwan
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Nguyen, Thanh Son
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Kamchoom, Viroon
;
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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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) (R2 = 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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Root biomechanical properties of Chrysopogon zizanioides and Chrysopogon nemoralis for soil reinforcement and slope stabilisation
(2021-10-01)
Phan, Trung Nghia
;
Likitlersuang, Suched
;
Kamchoom, Viroon
;
Leung, Anthony Kwan
Plant root reinforcement in soil bioengineering has gained increasing interest as a means of sustainable and environmentally friendly soil reinforcement and stabilisation. While Chrysopogon zizanioides is widely distributed in tropical regions worldwide and has been advocated for use in slope stabilisation and soil erosion control, C. nemoralis is normally distributed in mountainous areas in Southeast Asian countries, and its potential to reinforce soil has rarely been explored in the soil bioengineering literature. With the importance of root properties in soil bioengineering, this study was carried out to provide a comprehensive dataset of root biomechanical properties, morphological traits, and root reinforcement of these two contrasting vetiver species. A series of experiments, including root observation with a rhizobox system, uniaxial tensile test, and direct shear test, was performed. Results showed that Young's modulus and diameter of C. nemoralis roots were almost 1.4- and 1.3-times greater than those of C. zizanioides roots (p < 0.05). By contrast, no significant difference between the two vetiver species was observed in terms of tensile strength, 'side' root area ratio (RAR<inf>S</inf>), and root orientation (p > 0.05). The diameter–strength (R2 = 0.55–0.56, p < 0.05) and diameter–modulus relationships (R2 = 0.51–0.6, p < 0.05) of both species were consistent with negative power-law models. Conversely, their diameter–orientation relationship followed a linear model (R2 = 0.85–0.89; p > 0.05). The soil shear strength in terms of cohesion greatly increased in the presence of the roots of C. nemoralis (Δc = 4.9 kPa) and C. zizanioides (Δc = 4.4 kPa). Therefore, C. nemoralis could be an alternative to C. zizanioides in soil bioengineering applications.

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