The management of coal fly ash continues to transition from wet methods (e.g., sluice to settling ponds) to dry methods (compaction of ash into landfills). The closure of ash ponds and creation of ash landfills typically require designs which minimize infiltration and erosion. Impoundment practices such as dams for mine tailings and coal fly ash ponds accumulate constituents which, under certain conditions, may be hazardous to human health and the environment. Since most impoundments are exposed without protection, rain can induce erosion and generate leachate. Further, rain impact on ash erosion can cause massive ponding failures and resulting in spills. To monitor ash pond erosion process due to rain and possible use of chemical stabilization method to protect slope surfaces, terrestrial LiDAR is used to study simulated rain falls on ash slope. This paper reports laboratory studies using small-scale rain simulator and LiDAR scans to quantify mass loss due to rain impact.

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The aim of this research is to reveal the influence of internal erosion on mechanical properties by laboratory testing. Internal erosion is the transportation of fine particles with seepage flows inside the ground. A large degree of erosion induces various ground disasters, such as landslides and sinkholes. However, the influence of a small degree of internal erosion has not been examined. This is probably because the erosion progresses slowly, due to the repetition of seepage flows in the ground over a long period, without any obvious collapse or deformation. A new triaxial testing apparatus was developed in this study, that allows for a subtle amount of internal erosion inside the specimen. A field soil, containing around 10% clay, was used. Following the internal erosion, due to downward seepage, the specimen was monotinically sheared under a drained condition. LDTs and clip gages were mounted onto the specimen and the deformation characteristics were obtained during both erosion and monotonic shearing.

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This research aims to investigate the influence of characteristics of unsaturated soils on the stability of slopes subject to rainfall by using a coupled hydro-mechanical approach. In practice, distribution of the soil suction and moisture content at the shallow depth of a slope is considerably affected by the near-ground environment and climate change, e.g. vegetation, precipitation, evapotranspiration, and exposure to sun light, etc, and shallow slope failures are mainly governed by the unsaturated soil behavior at the shallow depth. The relationship between the soil suction and soil moisture content is important in characterizing the mechanical behavior of unsaturated soils. Parameters quantifying the soil-water characteristic curve (SWCC) are used to represent the characteristics of unsaturated soils. In addition, the degree of saturation at the residual state in the soil also affects SWCC, and the subsurface flow in a slope is governed by the hydraulic conductivity of the soil. Thus, influence of parameters (α, g, n) in SWCC, the hydraulic conductivity of the soil (K_sat) in saturated conditions, and the degree of saturation (S_r) at the residual state on the stability of slopes subject to rainfall is investigated. Major findings summarized from this research are: (1) α, n, and Sr values of the soil considerably affect the variation of the factor of safety (FS) of the slope with time during rainfall, specifically at the later stage of the rainfall activity. (2) Influence of m values on the stability of a slope during rainfall is minor. (3) The hydraulic conductivity at saturated conditions (Ksat) plays an important role in the stability of a slope during rainfall. Variation of the factor of safety of the slope with time during rainfall is not noticeable if the Ksat value of the soil is low.

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The damage to a dike caused by high water levels from a localized torrential downpour over a long period is presumed to be related to dike saturation from the seepage water from the dike surface and the blow off of pore air following a movement in the seepage line in the dike. The water flow generates a large-scale scour around the structure, and as a result, the stability of the structure is decreased. We discuss the ways in which multi-scaling problems and multi-phase interactions between soil, water, and gas affect these structures in three types of fundamental scour experiments. This study attempted to elucidate the scouring mechanism by experimenting using a movable bed channel device. During the water flow acting on the ground, a vertically upward hydraulic gradient along with excess pore water pressure was generated in the saturated ground, and a liquefaction-like phenomenon was generated by an increase the excess pore water pressure in the ground. Consequently, scouring was facilitated. The pore air in the unsaturated ground formed an air bubble due to seepage flow, and it spouted in the ground surface. The importance of the scour phenomenon of the dynamic interaction of soil particles, pore water, and pore air was discovered.

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Catastrophic landslides and debris slides triggered by intense typhoons such as Typhoon Morakot (2009) occurred more frequently in the recent years, and caused many casualties and economic loss in Taiwan. For the purpose of reducing the damage resulted from geological hazards, this study collects landslide inventories which contain the information of occurrence time, location, magnitude, rainfall intensity, accumulated rainfall and tries to establish the rainfall threshold for debris slide. This study adopts the concept of risk matrix, combining the magnitude (landslide ratio of slope units) and the possibility of occurrence (historical disaster records) to set up the warning thresholds. Critical rainfall thresholds are build up according to the R₂₄ (24 hours accumulated rainfall, as long-term rainfall) and I₃ (3 hourly mean rainfall intensity, as short-term rainfall) of historical disasters. Validation with recent typhoon event shows the threshold can forecast the landslides in 2~9 hours in advance which may be enough for the evacuation. An early-warning system is also built and the results can be applied to regional land-use planning and disaster prevention.

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Along the zone of interaction between land and water, there are continually changes due to dynamic interaction of water and land, so lots of problems occur such as Erosion, flooding, etc. Therefore riverbank and flood protection structures have become useful in the past decades. The National Road NR.01B is built along the mountainous area below the road is a river which flow parallel to the road alignment in soft shale area. There are 4 different stations which were investigated at KM90+600, KM 92+125, KM 92+212.5 and KM92+512.5. Unusually heavy monsoon rains, exacerbated by tropical storms, have caused widespread flooding in more than 60 per cent of the Lao PDR from late June through August. The monsoon rains continued since, and the country endured almost continuous heavy rainfall for some ten weeks. The forensic solution for erosion along the National Road is to use geosynthetic for improving the stability of the erosion protection structures. PLAXIS FEM 2D analysis was utilized to predict factor of safety for each station in case of low water and high water level. In each station of erosion protection structure used same soil parameter due to the same locations. The Slide Software was utilized to predict the value of factor of safety using Bishop, Janbu and Spencer methods in both cases of water level for each flood and erosion protection structure by using the same soil and support parameters which was used in PLAXIS FEM 2D Software. Moreover, comparing the best station between each erosion protection structures were carried out. Furthermore, comparing the results from PLAXIS FEM 2D and Slide Software, the result from PLAXIS 2D seems to have higher accuracy.

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Senise landslide in the southern Italy occurred in July 1986 due to the existence of a thin layer of clayey silt, interbedded with a slightly cemented sand formation. Excavation at the toe of the slope has lead to the occurrence of landslide. This is accompanied by progressive failure, mainly due to the softening behaviour of the thin clayey silt layer. The landslide is simulated using the developed finite element code that combines the Updated Lagrangian formulation and a strain softening model. This code is capable of simulating the development of the progressive failure. Simulation of slope failure in highly strain softening soils results in the distortion of finite element mesh; therefore, a proper numerical discretisation is prepared by an H-Adaptive remeshing technique to ensure that the analysis and leads to reliable results and solution convergence. The results of this study show the location and extent of failure zones. The failure is shown to be triggered by excavation at the toe of the slope and extends upward along the thin clayey silt layer. Compared with the observation, the numerical analysis could simulate the location of failure surface and the sliding soil mass reasonably well.

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