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 (RARS), 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.
Recently, random field copulas have been deployed to characterise the dependent structures of spatially variable soil parameters. This study expands on this concept by implementing finite element limit analysis (FELA) with adaptive meshing alongside the copula approach to perform reliability assessment of a geotechnical problem. A hypothetical slope with drained and undrained soil conditions was used as an example. First, adaptive FELA was carried out on the hypothetical slope. Second, single and multiple dependency soil parameter structures were represented by several selected copulas (Gaussian, Frank and Clayton). Finally, random adaptive FELA was implemented to explore the effects of copula selection on slope stability and reliability analyses. Results show that considerably different slope failure probabilities are produced by different copula approaches, and that failure probabilities reduce for simulating multiple dependency structures. In addition, failure probability exhibits different tendencies between drained and undrained soil conditions as soil parameter crosscorrelations become stronger. Failure probabilities are also different when performing lower and upper bound (UB) random adaptive FELA with each of the selected copulas.
Flue gas desulfurization waste (FGD) is one of coal combustion products (CCP) in coal-fired power plants. Mostly, FGD gypsum is applied in cement and wallboard industry. Also, it can be used in agricultural activities for soil amendment but the amount of FGD waste used in this function is still low. Furthermore, biochar has long been used to improve soil fertility. The positive impacts of biochar amendment on soils are that it can increase soil capacity to adsorb plant nutrients, decrease soil bulk density, increase plant available water retention and so on. In Thailand, some areas like Nan province has a problem of soil degradation from deforestation and excess use of chemical fertilizer. With the benefits of these FGD waste and biochar, the study of soil amendment will be performed by using degraded soil. Therefore, this research is aimed to apply FGD waste coupled with biochar to improve soil quality from degraded soil in Nan Province. Also, the objective of this work is to evaluate the effects of FGD waste and biochar on soil properties such as pH, electrical conductivity (EC), bulk density and soil texture. The concentrations of FGD waste and biochar are ranged from 5-25% and 5-30% by weight, respectively. The results present that the soil quality has been improved in that pH can increases from 5.664 up to 7.309. The soil texture has changed in the better quality from clay to silty loam or loam. Furthermore, the bulk density of soil is reduced in order to have more space for air and water for all mixture which is conducive to plant growth. Consequently, this research can contribute to the improvement of degraded soil properties to fit well for agriculture and the results can be applied for practice in the real field.
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 2 = 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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