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A Case Study of Soil Resistance Microzonation Based on Shear Wave Velocity
(2025-06-01)
Adrian, Mellanie Novita
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Mase, Lindung Zalbuin
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Hardiansyah, Hardiansyah
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Misliniyati, Rena
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Supriani, Fepy
This study, unique in its focus on the Kepahiang Regency, Bengkulu Province, aims to analyse soil characteristics and their potential impact on infrastructure stability using shear wave velocity (V<inf>s</inf>) data from 30 microtremor points spread across Kepahiang. The analysis produces a soil layer profile, shear wave velocity variations at various depths, Vs distribution maps, soil classifications, and ground amplification factors. The study reveals a significant risk of soil resilience effects in the area, primarily due to the dominance of class C soil, which consists of very dense soil and soft rock, and class D soil, which is rigid. The high amplification factor caused by the low average shear wave velocity to a depth of 30 m also affects soil resistance. This research contributes significantly to geotechnical risk mitigation efforts, safer spatial planning, and infrastructure development resistant to landslides in the Kepahiang Regency.
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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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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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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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Shearing behaviour of vegetated soils with growing and decaying roots
(2022-12-01)
Kamchoom, Viroon
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Leung, Anthony Kwan
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Boldrin, David
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Sakolpanya, Tapakorn
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Wu, Zhaoyi
Plant roots affect the soil shear strength, but the temporal dynamics of roots such as growth and decay due to different mortality means have rarely been considered. This study investigates the effects of root growth and decay on the changes in root biomechanical properties and the shearing behaviour of vegetated soils. Columns of compacted soils were grown with a grass species, Cynodon dactylon. The grass was grown for 6 months, followed by burning or herbicide applications to introduce root decay. The top part of each column was used for direct shear tests, whilst the roots collected from the bottom part were used for the measurements of root tensile and chemical properties. The vegetated soils displayed greater shear strength and larger dilatancy, which were attributable to the growth-induced increase in the root cellulose content, and thus the root tensile strength and modulus. Root decay, upon burning or herbicide use, caused significant declines in the root tensile properties, which translated to the reductions in soil dilatancy and soil shear strength lower than those of the fallow soil. Herbicide use introduced a much faster and significant loss of root reinforcement than burning because of the more severe decay and loss of root biomechanical properties.
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Destructive and nondestructive characteristics of solidified reservoir sediments incorporating microstructural analyses
(2022-08-01)
Jamsawang, Pitthaya
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Poorahong, Hatairat
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Jongpradist, Pornkasem
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Likitlersuang, Suched
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Chaiyaput, Salisa
Reservoir sediments create a range of severe problems for hydropower dams. Although reservoir sediments can be excavated, nonetheless, sizeable dumping lands for such excavated sediments are unavailable at this time. This paper presents an experimental investigation of the destructive and nondestructive properties and microstructural characteristics of reservoir sediments solidified with fly ash–cement blend for reuse as construction materials. The obtained natural sediment was classified as well-graded sand with silt. The destructive experiments comprised unconfined compression, indirect tension, California bearing ratio, resilient modulus, and durability against wet–dry cycle tests, while the nondestructive experiments included a free–free resonance test. Microstructural investigations consisting of X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectrometry were performed to verify the macroscale test results. The results showed that fly ash–cement blend exhibited increased strength values on the order of 2 to 9 times that of unsolidified sediments. Using fly ash-blended cement was more effective than using sole cement or sole fly ash, and mixtures with 10% fly ash delivered the best strength and modulus values. Various functional empirical correlations were proposed. Utilizing six wet–dry cycles is acceptable because the strength of the samples subjected to the six wet–dry cycles was lower than the given value. The results of the peak intensities of calcium silicate hydrate, mass losses, calcium contents, and scanning electron microscopy images derived from the microstructural investigations confirmed the macroscale test results.
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Biomechanical properties of the growing and decaying roots of Cynodon dactylon
(2022-02-01)
Kamchoom, Viroon
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Boldrin, David
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Leung, Anthony Kwan
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Sookkrajang, Chanakan
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Likitlersuang, Suched
Aim: Root growth and decay may affect root reinforcement to soil erosion and stability. We measured the effects of growth and decay on the tensile strength of Cynodon dactylon roots considering different causes of mortality common to agricultural land conversion (i.e. burning and herbicide application). Method: We applied three treatments to C. dactylon grass: (i) growth duration (60, 120 and 180 days), (ii) decay duration after burning (30, 60, 120, 180 and 360 days) and (iii) decay duration after herbicide application (15, 30 and 60 days). The diameter, tensile strength and cellulose and lignin contents of root samples (n = 303) in different treatments were measured. Results: Tensile strength–diameter relations followed a negative power law regardless of treatment (R2 > 0.6). The increase in median tensile strength values due to grass growth was consistent with the increase in cellulose and lignin contents. Root decay by herbicide application caused significantly greater and faster reduction in tensile strength than burning treatment because of the faster reduction of cellulose and lignin contents. Conclusion: Root decay due to different causes of plant mortality can increase susceptibility to erosion and slope instability during the conversion of agricultural land. Measures on slope safety and erosion are vital when using herbicides for weed clearance in farmlands due to the faster deterioration of root chemical composition and root tensile strength (compared with burning).
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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
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Likitlersuang, Suched
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Kamchoom, Viroon
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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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Simplified finite-element modelling for tunnelling-induced settlements
(2014-12-01)
Likitlersuang, Suched
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Surarak, Chanaton
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Suwansawat, Suchatvee
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Wanatowski, Dariusz
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Oh, Erwin
Tunnelling-induced ground surface settlement prediction still adopts empirical and analytical approaches; thus a step further in using a practical numerical analysis is now a challenging task. Because the deformation during tunnelling is a three-dimensional problem, several features were incorporated in two-dimensional analyses to capture aspects that are important in governing behaviour in the missing third dimension. This paper aims to present simplified methods for ground settlement computation of tunnelling works using the PLAXIS finite-element programme. Three simplified methods – contraction ratio, stress reduction and modified grout pressure – were considered in this study. Practical application requires correlations among these three methods. Such correlations among the three methods are proposed in this study and can be used in geotechnical practice. The results were based on a series of finite-element analyses of the Blue Line Bangkok Mass Rapid Transit tunnels. The geotechnical parameters were selected based on soil investigation reports carried out for construction purposes. The soil constitutive model adopted herein was the hardening soil model on soft and stiff clays. All the finite-element simulations were compared with the measured field deformations. Therefore, the analysis results can be considered as a Class-C prediction (back-analysis).

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