Valley bulging

Valley bulging In Interbedded shales and thin sandstones of Namurian age revealed during the excavation for the dam for Howden Reservoir in 1933, South Yorkshire, England. 

Earth dams are usually constructed on clay soils as they have insufficient load-bearing properties required to support concrete dams. Beneath valley floors, clays may be contorted, fractured and softened due to valley bulging so that the load of an earth dam may have to spread over wider areas than is the case with shales and mudstones. Settlement beneath an embankment dam constructed on soft clay soils can present problems and may lead to the development of excess pore water pressures in the foundation soils (Olson, 1998). Rigid ancillary structures necessitate spread footings or raft foundations. Deep cuts involve problems of rebound if the weight of removed material exceeds that of the structure. Slope stability problems also arise, with rotational slides being a hazard. 

The surface can be characterized either as external when it involves bulges or cavities with width greater than the depth, or as internal when it involves pores and cavities that have depth greater than the width (Gregg and Sing, 1967). All surfaces are not really smooth and they exhibit valleys and peaks at a microscopic level. These areas are sensitive to force fields. In these areas, the atoms of the solid can attract atoms or molecules from a fluid nearby. 

---