Search

Channel centreline migration rates were derived from a set of large-scale laboratory experiments. The channel radius of curvature, bend angle, and discharge were varied to evaluate correlations between the channel centreline migration rate and the controlling geometry and hydraulic conditions. An excessive Froude number was adopted to account for soil resistance strength. The intersection of the channel centreline between two consecutive time steps was identified. A phase lag of angle to channel curvature exists in both channel plan form and the onset of cross-section scour. The migration rate between two successive inflection points of migration exhibits a growth and decay pattern and is modelled using a sine function related to the channel geometry, the flow condition, and the soil property. A three-equation prediction method was developed and applied to a natural river in Texas. [ABSTRACT FROM PUBLISHER]

Lane/shoulder drop-off or heave due to expansive soils beneath is a common distress in both concrete and asphalt pavements, resulting in substantial discomfort, safety hazard and vehicle damage. The situation becomes worse when exposed to moisture changes, particularly in Texas, Colorado, Arizona, California, etc. where many soils are expansive soils. Therefore, expansive soils pose great challenges for the design of pavements and foundations. One of the most difficult issues for designing pavements and foundations on expansive soils is to predict the volume change of the soils. In this study, current methods for movement predictions are summarised and their relationships and shortcomings are discussed. It is found that all these methods have the same theoretical basis. Based on the theory of unsaturated soil mechanics, it is found that the water content and the mechanical stress can be used to determine the soil status. Hence, a void ratio versus mechanical stress and water content surface is constructed, which coupled both mechanical stress and suction's influences on volume change of expansive soils. The new surface is developed into a coupled water content method that can be used to predict the potential vertical swell and the potential vertical shrink simultaneously, while all the existing methods can only predict the potential vertical rise. The method is used to analyse the data collected from a construction site at Arlington, Texas. The predicted movements match the measured data reasonably well. The method is simple and overcomes the shortcomings existing in the current movement prediction methods for expansive soils. [ABSTRACT FROM AUTHOR]