Experiments on Channel Evolution Caused by Check-dam Failure

A 10 m long,0.2 m wide flume was employed to simulate the channel bed evolution of check-dam failure.The experiment longitudinal profiles,the gradient of channel bed,head-cutting propagation distance and deposition length were compared with the theoretical solution derived from a sediment transport diffusion equation.In contrast with the theoretical solution,two different gradients were obtained upstream and downstream of the check-dam.The theoretical solution provides a good description of the changes upstream of the check-dam. The ratio of clear water depth to sediment moving layer thickness in the experiment was analyzed and showed that high concentration sediment laden flow was taken in the incipient of check-dam failure,which may be the reason why the experiment result was slightly different from the theoretical solution in the downstream of check-dam.

Hydro-mechanical response with respect to the air ventilation for water filtration in homogeneous soil

When water penetrates into soil,interstitial air can become trapped by the infiltrating water.Neglecting the effect of air ventilation could cause deviations in the predicted pore water pressure and the associated effective stress.This study aims at the effect of air ventilation on the coupled hydro-mechanical responses in homogeneous soil during infiltration.A schematic concept of infiltration conditions(open-and closed-valve)in homogeneous soil is proposed for investigating their impacts on the pore water pressure and effective stress.Experiments of vertical soil column filled with Ottawa sand(ASTM C77820/30)were designed for two types of air ventilation(namely,open and closed infiltration).The evolution of pore water pressure at the cylinder bottom was recorded,and served as a benchmark problem for evaluating the coupled hydro-mechanical response.Coding with the commercial software,GeoStudio,was employed for the dynamic behaviors of pore-water and-air pressures as well as the evolving effective stress.It was found in both the experiments and numerical investigations that the infiltration condition plays a crucial role for the ascending rate of pore water pressure as well as the associated effective stress.These results illustrate the inevitable impacts of the air ventilation conditions on the mechanical properties of the soil during infiltration.

Rapid Geometry Analysis for Earthquake-induced and Rainfall-induced Landslide Dams in Taiwan

Stability analysis of the dam is important for disaster prevention and reduction. The dam's geometry plays an important role in understanding its stability. This study develops a rapid landslide dam geometry assessment method for both earthquake-induced and rainfall-induced landslide dams based on nine real cases collected in Chinese Taipei and 214 cases collected worldwide. For simplification purposes, a landslide dam is classified into triangular or trapezoidal. The rapid landslide dam geometry assessment method in this paper uses only satellite maps and the topographic maps to get landslide area, and then analyze the dam geometry. These maps are used to evaluate the area of the landslide and the slope of the river bed. Based on the evaluation information, the proposed method can calculate dam height, the length of the dam, and the angles of the dam in both upstream and downstream directions. These geometry parameters of a landslide dam provide important information for further dam stability analysis. The proposed methodology is applied to a real landslide dam case at Hsiaolin Village. The result shows that the proposed method can be used to assess the landslide dam geometry.

Sediment control function of river notches

The purpose of this study is to investigate the control function and mechanisms of natural river notches. Physical and numerical experiments are analyzed in this study for two representative types of sediment events: high intensity and short duration Type A sediment disaster events, and low intensity and long duration Type B moderate non-disaster events. Two dimensionless parameters, sediment trapping rate and reduction rate of peak sediment transport, are defined to evaluate the sediment control function of river notches. Study results indicate that the contraction ratio of the notch has a significant influence on sediment control function, with high contraction ratios resulting in both high sediment-trapping and high reduction rates. River notches provide better sediment control during Type A events than Type B events. The sediment control mechanism of river notches is the result of multiple interactions among river flow, sediment transport, and riverbed variation. Analysis of these interactions supports the significant protection role of river notches on sediment control for disaster