The study presents a numerical infiltration model of a hysteretic flow coupled with general mass conservation for practical application to unsaturated soil. In unsaturated soil, hysteresis is an important phenomenon in the complicated hydrological processes, and it is usually ignored when simulating the relationship of soil water content. The governing equation of unsaturated flow is the Richards equation, and it is difficult to obtain the analytic solutions because of the variation of temporal boundary conditions and the dynamics of change of soil water content in the vadose zone. The numerical solution is solved by the finite difference method technique with the Picard iteration scheme combined with the hysteresis model derived by Huang et al.

Abstract:Hysteresis is a common feature exhibited in hydraulic properties of an unsaturated soil. The movement of wetting front and the hysteresis effect are important factors which impact the shear strength of the unsaturated soil and the mechanics of shallow landslides. These failures are mainly triggered by the deepening of the wetting front accompanied by a decrease in matric suction induced by infiltration. This research establishes a method for determining a stability analysis of unsaturated infinite soil slopes, integrating the influence of infiltration and the water retention curve hysteresis. Furthermore, the present stability analysis method including the infiltration model and the advanced Mohr-Coulomb failure criterion calculates the variations of the safety factor (FS) in accordance with different slope angle, depth and hydrological processes. The experimentally measured data on the effect of hysteresis are also carried out for comparison. Numerical analyses, employing both wetting and drying hydraulic behaviour of unsaturated soil, are performed to study the difference in soil-water content as observed in the experiments. The simulating approximations also fully responded to the experimental data of sand box. The results suggest that the hysteresis behaviour affect the distribution of soil-water content within the slope indeed. The hysteresis made the FS values a remarkable recovery during the period of non-rainfall in a rainfall event. The appropriate hydraulic properties of soil (i.e. wetting or drying) should be used in accordance with the processes that unsaturated soil actually experience. This method will enable us to acquire more accurate matric suction head and the unsaturated soil-shear strength as it changes with the hysteretic flow, in order to calculate into the stability analysis of shallow landslides. An advanced understanding of the process mechanism afforded by this method is critical to realizing a reliable and appropriate design for slope stabilization. It also offers some immediate reference information to the disaster reduction department of the government.

This paper presents an analytical model for describing the tidal effects in a two‐dimensional leaky confined aquifer system in an estuarine delta where ocean and river meet. This system has an unconfined aquifer on top and a confined aquifer on the bottom with an aquitard in between the two. The unconfined and confined aquifers interact with each other through leakage. It was assumed that the aquitard storage was negligible and that the leakage was linearly proportional to the head difference between the unconfined and confined aquifers. This model's solution was based on the separation of variables method. Two existing solutions that deal with the head fluctuation in one‐dimensional or two‐dimensional leaky confined aquifers are shown as special cases in the present solution. Based on this new solution, the dynamic effect of the water table's fluctuations can be clearly explored, as well as the influence of leakage on the behaviour of fluctuations in groundwater levels in the leaky aquifer system. Copyright © 2015 John Wiley & Sons, Ltd.

Taiwan is surrounded by the sea, and the southwestern seashores are suffering from a growing land subsidence problem caused by the excessive extraction of groundwater. There is also very serious intrusion by seawater along the coastline. These circumstances obstruct any land use, soil remediation or agriculture development in the area. When seawater intrudes, salt gets into the soil. The infiltration, evapotranspiration and the distribution of salinity in the unsaturated soil become a very complex problem. It is vital to investigate the hysteresis of soil water-retention curves, combined with the salinity in these areas. Therefore, this study's main focus will be the calibration of variations in salinity and their effect on the hysteresis of soil waterretention curves. In the wetting processes, the salty soil water-retention curves undergo an upper shift compared with the original soil water-retention curves because of the higher tension of saltwater. In the drying processes, there is also an upper shift compared with the original curves because the salinity influences the air-entry pressure. The saltwater's high salinity causes the hysteresis of soil water-retention curves to experience a greater shift. The changes in salinity also cause changes to the hysteresis curves' shape factors, which conforms to Huang's model (developed in 2005), the values of a and n. The value of a decreases with the increased salinity. The trend of the n value presents an irregular result. A linear regression of the a w and a d values was advanced where the R-square values of a w and a d exceeded 0.97.

The purpose of this paper is to present sand-box experiments and a hysteresis model to explain the formation and hydraulic properties of fingered flow. Previous researches have found that a fingered path persists over long periods of constant infiltration; hysteresis could be an important factor. In this paper, a major point is to utilize the boundary and series internal scanning curves of the hysteresis model derived by Huang et al. (2005) to clearly obtain the variations between soil water content (u) and matric suction head (c). The hydraulic properties of fingered flow are also acquired. For the application of the model in the field, the hysteresis curves derived by Hogarth et al. (1988) are compared. Experimental results verified that both hysteresis models and the present soil water content concept model of fingered flow can be adequately applied in field tests. We attempted to use digital image analysis to visualize and determine soil water content of fingered flow easily and quickly. The initial velocity and width of fingered flow were not constant under consistent rainfall intensity. The present concept model showed the matric suction head is uniform between different soil water content sharply in the horizontal direction. Nonuniform soil water content existed even when the potential was horizontally equalized. Copyright # 2008 John Wiley & Sons, Ltd. hauteur d'aspiration est uniforme selon différentes himidité sol en particulier en direction horizontale. Une humidité non uniforme existe même quand le potentiel est lissé horizontalement.