Although vegetation is increasingly used to mitigate landslide risks, how vegetation roots affect the landslide threshold of slope has rarely been explored, particularly in the case of lateral runoff. In this study, we established a two-dimensional saturated-unsaturated infiltration equation considering the hydraulic effects of vegetation roots. The analytical solution for the shallow unsaturated two-dimensional coupled infiltration of vegetated slope (VS) was obtained by a Fourier transform technique. The numerical method was used to evaluate the stability of VS caused by four root architectures, the rainfall amount, and the rainfall duration. Subsequently, the transformation law in runoff, vegetation evaporation, and landslide threshold was analyzed. The results indicate that the factor of safety (FOS) increases with increasing drying time and decreases with increasing depth; the minimum FOS is at the junction of the root-rootless zone. Runoff and vegetation evaporation are favorable for the shallow stability of VS. The time of the safe area is 35 h for rainfall amount 500 m in the uniformly root clay slope. Moreover, four landslide threshold curves that reflected the root architecture, rainfall amount, and rainfall duration are developed, which are more realistic than those created using one-dimensional instability modeling.
Strength of vegetated coal-bearing soil is of great significance to evaluate the shallow stability of vegetated slopes in coal-bearing soil regions. This paper takes D-W cycles, dry density, water content, and vegetation root (VR) content as four factors and carries out the triaxial test for the orthogonal design of vegetated coal-bearing soil in southern China. The strength curves of vegetated coal-bearing soil under four factors were obtained. The Taguchi method was used to quantitatively analyse the effects of four factors. The microstructure of coal-bearing soil under D-W cycles and the theory of soil reinforcement by VR were discussed. The results indicated that D-W cycles had a significant effect on the cohesion and internal friction angle ( P < 0.05 ). The internal friction angle was little affected by the water content and VR content, which had considerable influence on the cohesion. The cohesion could be improved with less than 2% VR content. The cohesion was the largest for no D-W cycles, 10% water content, and 2% VR content. The links between mineral particles go from a stable layered structure to unsteadiness chain structure with the increase in the number of D-W cycles.
Ecological restoration is of profound significance for protecting the ecology and engineering safety of coal-bearing soil (CBS) areas. However, the formulations of CBS ecological substrates have rarely been explored. The objective of this study was therefore to evaluate the effects of the CBS:soil ratio (1000:0 g, 750:250 g, 500:500 g, 250:750 g), fly ash content (0, 50 g·kg− 1, 100 g·kg− 1, 150 g·kg− 1), maize straw content (0, 20 g·kg− 1, 40 g·kg− 1, 60 g·kg− 1), and expanded polystyrene (EPS) content (0, 3 g·kg− 1,6 g·kg− 1, 9 g·kg− 1) in an orthogonal design to optimize an ecological substrate according to various physicochemical, nutrient content, mechanical, and vegetation parameters. The results indicated that the CBS:soil ratio had significant effects on the nutrient content and vegetation growth parameters; fly ash dramatically improved the mechanical parameters (shear strength, cohesion, and internal friction angle); maize straw significantly affected the physical parameters and improved the substrate nutrient content; and EPS was the most beneficial to the vegetation germination ratio. A CBS:soil ratio of 1:1 (500:500 g), fly ash content of 100 g·kg− 1, maize straw content of 50 g·kg− 1, and EPS content of 6 g·kg− 1 were determined to produce the optimal mix for the ecological restoration of CBS. The conclusions of this research provide theoretical and practical guidance for the ecological restoration and stabilization protection of CBS slopes.
Exposed coal measure soil (CMS) found in the mountains of Southern China is significantly affected by the seasonal climate, which makes this region prone to frequent shallow landslides. In this regard, very few studies have focused on the shear strength and microscopic characteristics of CMS subjected to dry–wet cycling and temperature. The aim of this study was to experimentally investigate the effects of dry–wet cycling and temperature on shear strength and microscopic parameters of CMS. We carried out an unconsolidated undrained triaxial test and scanning electron microscopy of CMS obtained from the K209 slope on the Chang-li highway. Our results indicated that the soil shear strength and microstructure parameters significantly decreased before three dry–wet cycles. Above 35 °C, the temperature affected mainly the mean fractal dimension. The soil cohesion was negatively correlated with the fractal dimension and positively correlated with the probability entropy. The surface-crack occurred once the stress value of high temperature was greater than 0.57 MPa. Strain-softening, swelling–shrinkage, low soil strength, and high soil temperature formed the main factors underlying rainfall-induced K209 shallow landslides.
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