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The ecological function optimization strategy of vegetation directly affects the self-stability and engineering sustainability of the vegetation concrete ecological restoration system, which is the key to the successful restoration of an ecosystem. To clarify the survival strategies of slope protection plants and their response mechanisms to the soil environment in the process of vegetation concrete ecological restoration, the resource allocation strategies and soil driving factors of typical slope protection plants, such as Cynodon dactylon (Linn.) Pers. and Indigofera amblyantha, in a co-operation environment mode, were investigated by controlled simulation experiments. The results showed that (1) the co-operating environmental model had a significant effect on the biomass (leaf, stem and root) and root shoot ratio of slope protection vegetation; (2) the sensitivity of plant biomass in the co-operating environmental model was leaf biomass ratio > root biomass ratio > stem biomass ratio, and the most sensitive organ was the leaf; (3) a common allometric growth index for the plants of all slopes existed, the root and leaf grew at the same rate, and the plant roots and stems showed allometric growth with the synergistic effect of rainfall and slope; (4) the total nitrogen content of soil had a significant correlation with the vegetation R/S (root shoot ratio) (p < 0.05) due to the synergistic effect of vegetation type and slope, while the total phosphorus content of the P3 slope had a significant negative correlation with the vegetation R/S (p < 0.05). The co-operating environmental model significantly affected the spatial distribution of vegetation biomass and had the greatest impact on leaf biomass. The contents of soil nitrogen and phosphorus were the key soil driving factors that affected the distribution pattern of plant biomass. The resource allocation characteristics of different vegetation and its response to soil factors had species specificity.

Vegetation can enhance the stability of slopes by increasing the shear resistance of the soil. Shear stress applied to the soil matrix is resisted by the pullout strength of the roots via the friction at contact points between the soil and the roots. The effectiveness of root reinforcement depends on interface friction between soil and roots. In this study, tests were carried out on Indigofera amblyantha Craib roots, by measuring resistance as they are pulled out of the soil where the soil has varying dry densities. The results reveal three phases in the relationship between the pullout force and the slippage of the roots, i.e. (1) steep rise, (2) steep fall, and (3) gradual decline. In the first phase, the pullout force is increasing sharply and linearly up to a maximum when the slippage is about 10mm. With continued slippage, the required pullout force decreases significantly and nonlinearly in up and down fluctuations. Eventually, the pullout force reaches zero. For soil with a given dry density, the maximum pullout force increases linearly with increasing root diameter, and the correlation coefficient is greater than 0.9. Further, for a root with a given diameter, the maximum pullout force increases with increasing soil dry density. When the root breaks on pulling, it is called tensile failure; when the root is fully pulled out, it is called friction failure. The mode of failure for all roots is friction failure, for soil with dry densities of 1.35 g/cm3, 1.45 g/cm3, and 1.55 g/cm3. For soil with a dry density of 1.65 g/cm3, and root diameter under 0.716 mm, the observed failure mode is generally tensile; for diameters over 0.716 mm, the failure mode changes to friction; that is, thin roots break, thick roots get pulled out

Rainfall events coupled with shallow and gravelly sloping farmland have led to serious soil erosion and associated problems in the Three Gorges reservoir. Previous studies have shown that the use of vegetation is an effective way to control soil erosion. Therefore, an artificial, simulated rainfall experiment study is conducted to determine the effect of rainfall intensity and vegetation cover on runoff volume, sediment load, and runoff hydraulics characteristics. The experiment consists of seven vegetation treatments subjected to three rainfall intensities on a soil that contains rock fragments on a slope of 30°. The results indicate that the runoff volume and sediment load of the bare plot were greater than those of vegetation-covered plots under three different rainfall intensities. When Cynodon dactylon and Indigofera amblyantha were applied together, the plot displayed the best performance for soil loss control, with a reduction of 87.88%–99.11%. According to a redundancy analysis, the change in rainfall intensity had the least impact on the Reynolds number and the runoff volume of the herb-shrub mixed plot in this study. These findings suggest that the effect of combining Cynodon dactylon and Indigofera amblyantha and increasing the vegetation coverage is an effective solution for soil and water loss conservation. The application of this method can alleviate environmental stress on the Three Gorges reservoir.

Vegetative porous concrete (VPC) could effectively reduce the adverse impacts of engineering construction on the environment and adapt to the demands of sustainable development. In this article, sh...

The overland flow erosion is common and became more serious because of the climate warming inducing more runoff in the Tibet Plateau. The purposes of this study were to evaluate the effects of flow rate, slope gradient, shear stress, stream power, unit stream power and unit energy of water-carrying section on the soil detachment capacity for the soil in the Tibet Plateau of China due to the information is limited. To achieve this aim, laboratory experiments were performed under six flow rates (5, 10, 15, 20, 25 and 30 L min−1) and six slope gradients (8.74%, 17.63%, 26.79%, 36.40%, 46.63 and 57.73%) by using a slope-adjustable steel hydraulic flume (4 m length, 0.4 m width, 0.2 m depth). The results indicated that soil detachment capacity ranged from 0.173 to 6.325 kg m−2 s−1 with 1.972 kg m−2 s−1 on average. The soil detachment capacity increased with power function as the flow rate and the slope gradient augmented (R2 = 0.965, NRMSE = 0.177 and NSE = 0.954). The soil detachment capacity was more influenced by flow rate than by slope gradient in this study. The relation between soil detachment capacity and shear stress, stream power, unit stream power and unit energy of water-carrying section can be described by using the linear function and power function, the power function relationship performed better than the linear function in generally. The stream power exhibits the best performance in describing the soil detachment capacity among shear stress, stream power, unit stream power and unit energy of water-carrying section in this study. The erodibility value in this study was larger than and the critical shear stress was less than those for soil in the eastern China. There has a huge potential for the soil in the Tibet Plateau eroded by the water erosion when enough runoff exiting. More attention should be payed to the water erosion process and mechanism in the Tibet Plateau area in the future.

Soil aggregates are the basic unit structing soils, and their stability is an important index for soil degradation. However, current methodologies rarely assess the influence of primary soil particles on soil aggregates distribution for different breakdown mechanisms. The purpose of this study was to fill this gap in the literature by developing a new method that separates the primary soil particles from the soil aggregates for different breakdown mechanisms with a series of in-lab experiments. The whole soil sample was treated by fast wetting, slow wetting, and mechanical breakdown by pre-wetting and stirring to simulate the different breakdown mechanisms of slaking, differential swelling of clays, and mechanical breakdown by raindrop impact, respectively. Then, attempts were made to separate the primary soil particles from the soil aggregates of various particle size fractions by using sodium hexametaphosphate and hydrogen peroxide to eliminate the influence of the primary soil particles on the soil aggregate distribution. Four soils collected from different areas with different soil textures were used to assess the soil aggregate distribution by using the new method to highlight the importance of separating the primary soil particles from the soil aggregate for different breakdown mechanisms. The results indicated that the primary soil particles have much greater influence on the micro-aggregates than on macro-aggregates. Different breakdown mechanisms and soil types could affect the influence of the primary soil particles affects the on soil aggregate distribution. This study highlights the influence of separate primary soil particles on soil aggregate distribution for different breakdown mechanisms.

To select and improve techniques capable of eco-restoration and reconstruction of soils, it is vital to determine the impacts of different engineered eco-restoration techniques on communiti...

Vegetation concrete is one of the most widely used substrates for slope ecological protection in China. However, there are still some imperfections that are disadvantageous for plant growth, such as high density, low porosity, insufficient nutrient retention ability and so on. In this paper, the effect of wood activated carbon and mineral activated carbon on the physicochemical properties of vegetation concrete is studied. The experimental results show that the activated carbon proportion in vegetation concrete is positively related to the porosity, permeability coefficient, water holding capacity, and nutrient content and retention ability, while it is negatively related to the dry density, water retention ability, cohesive force and internal friction angle. However, it should be noticed that when the proportion exceeds 2%, the average height, aboveground biomass and underground biomass of Cynodon dactylon decrease with increasing proportion of activated carbon. The effect of wood activated carbon is generally more remarkable than that of mineral activated carbon. In addition, according to the research results, the effect of activated carbon on vegetation concrete can last for at least half a year, although it does slowly deteriorate with increasing time. By comprehensive consideration of the current industry standard, previous research results and economical reasoning, the recommended type of activated carbon is wood, with a corresponding suitable proportion ranging between 1 and 2%.

Background To quantitatively evaluate the contribution of plant roots to soil shear strength, the generalized equivalent confining pressure (GECP), which is the difference in confining pressure between the reinforced and un-reinforced soil specimens at the same shear strength, was proposed and considered in terms of the function of plant roots in soil reinforcement. Methods In this paper, silt loam soil was selected as the test soil, and the roots of Indigofera amblyantha were chosen as the reinforcing material. Different drainage conditions (consolidation drained (CD), consolidation undrained (CU), and unconsolidated undrained (UU)) were used to analyse the influences of different root distribution patterns (horizontal root (HR), vertical root (VR), and complex root (CR)) and root contents (0.25%, 0.50%, and 0.75%) on the shear strength of soil-root composites. Results The cohesion (c) values of the soil-root composites varied under different drainage conditions and root contents, while the internal friction angle (φ ) values remain basically stable under different drainage conditions. Under the same root content and drainage conditions, the shear strength indexes ranked in order of lower to higher were HR, VR and CR. The GECP of the soil-root composites with a 0.75% root content was 1.5–2.0 times that with a 0.50% root content and more than 5 times that with a 0.25% root content under the CD and CU conditions. The GECP in reinforced soil followed the sequence of CD > CU > UU. The GECP of the plant roots increased as confining pressure increased under CD and CU conditions while showed a complex change to the confining pressure under the UU condition. Conclusion It was concluded that the evaluation of plant root reinforcing soil based on GECP can be used to measure effectively the influences of roots on soil under different drainage conditions and root distribution patterns.

Vegetation concrete is a typical artificial composite soil commonly used for ecological restoration on slopes. The strength and stability of vegetation concrete would be reduced when it is used in ...

Vegetation-concrete is one of the most widely used substrates in ecological slope protection engineering. The porosity of the vegetation-concrete must be high enough to satisfy the growth needs of the plant roots, while the mechanical properties must be strong enough to satisfy the self-stability requirement of the substrates on the slope. It is necessary to balance these two aspects in the design of vegetation-concrete. As one of the main components in vegetation-concrete, organic material has a remarkable effect on both the porosity and the mechanical properties of the substrate. In this paper, four types of common organic materials (rice husks, sawdust, and corn distillers’ and unhulled rice distillers’ grain) are chosen to research the effect of the organic material type and proportion on the porosity and mechanical properties of the substrate. The experimental results show that the porosity of samples containing corn distillers’ grain is clearly higher than those of the other samples types, while situation of the mechanical properties is the opposite. It can be concluded that organic material with a large grain size is not suitable for use in vegetation-concrete directly and needs to be crushed before use to prevent crack formation. The research results also show that the rates of increase in porosity decrease with more organic material added, while the rates of decrease in the unconfined compressive strength and the elasticity modulus increase. From a comprehensive consideration of the required mechanical properties and plant growth, organic material with a small grain size is most suitable for use in vegetation-concrete, and the suitable proportion is between 7% and 9%.

The erosion of the highway embankment slope's soil along the Wad Medani-Sennar road is a significant issue, as there are many traffic accidents on this road, with an average of 15 to 25 fatalities per annum. It was thus decided to investigate this issue to find a method to protect slope from erosion on this road and to provide new approaches to slope erosion knowledge gap in Sudan. An engineering survey was carried out, followed by geotechnical studies, experimental work and interviews with academic experts regarding native vegetation in the survey area. These include measuring the eroded parts of the road; studying cross- sections of the road; soil experiments to check the strength, compaction and particle size distribution; and a native vegetation survey to check for suitable plants that could be used to control the slope erosion. It was found that an appropriate bio-engineering method to stabilize the slope soil against erosion due to rainfall was to cultivate the grasses Cynodon Dactylon and Vetiver on the slopes. In conclusion, that using native vegetation for eco -protection, was an excellent solution to the problem based on the climate, native vegetation, and type of soil in Sudan and it reduces the accidents.