ABSTRACT:Currently the Metropolitan Area of San Salvador (AMSS) is experimenting serious problems of mass movements, erosion, collapse or settlements, phenomena that in El Salvador are popularly encompassed by the term "carcavas". This problematic is presented mainly in the volcanic tephras Tierra Blanca Joven (TBJ), product of the last plinian eruption of Ilopango Caldera, whose products are an intercalation of pyroclastic fall, flows and surge. The tephras are unsaturated and the geotechnical information shows a decrease of shear strength and collapse when saturated. To characterize properly this material is important to know the relationship of moisture content with the volume changes and apparent cohesion, which are related to suction and cementation. The understanding of the behavior of the geological materials can help in running slope stability simulations and geotechnical design in general.
In El Salvador during the rainy season or when major earthquakes occur, the areas covered by the volcanic tephras Tierra Blanca Joven (TBJ) suffer mass movements, liquefaction and erosion; causing important environmental, social and economic losses. To start the characterization of these unsaturated soils, suction values of a fall unit of TBJ were obtained using pressure plate, centrifuge and filter paper to build a Soil-Water Retention Curve. The use of this curve into finite elements software can help to acquire shear strength and permeability properties. The filter paper showed to be a practical method but close to saturation the pressure plate is needed. With the centrifuge, scatter results were observed. Also field test using Quickdraw tensiometer (suction) and TMS3 (soil moisture content) are being conducted to propose a field methodology for an early warning system for the slopes, that could help in urban planning and risk assessment.
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