Neutral Pressures in Compacted Cohesive Soils

by Francisco P. Silva,

Serial Information: Journal of the Soil Mechanics and Foundations Division, 1966, Vol. 92, Issue 1, Pg. 105-120

Document Type: Journal Paper

Abstract: Observation of neutral pressures in four earth dams in Brazil showed negative values in some cases, negative evolving to positive, or only positive values in other instances. The soils used were of two different types. A first type, a medium plastic clay originated from in situ weathering of gneiss, and a second type, a colluvial medium plastic clay originated from basalt. The main feature regarding the observed negative neutral pressures is that the water tension was found to increase with increasing load application, to a certain value. An assumption is advanced to explain this behavior by considering a partly saturated equivalent capillary tube whose diameter decreases with external load application, thus resulting in higher water tensions. This behavior is observed for low degrees of saturation; for degrees of saturation approaching 100%, positive neutral pressures tend to appear. It is suggested that this change in behavior occurs at degrees of saturation in which air paths cease to be interconnected.

Subject Headings: Compacted soils | Soil pressure | Load factors | Plastics | Tension | Clays | Earthfill dams | Field tests | Developing countries | Brazil | South America

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