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CHARACTERISTIC SHEAR STRENGTH VALUES FOR EC7: GUIDELINES BASED ON A STATISTICAL FRAMEWORK (2011)
Geotechnical performance of a structure is generally governed by spatial average soil properties, such as the average shear strength along a potential slip surface in a slope. In Eurocode the characteristic soil value is defined as “a cautious estimate of the value affecting the occurrence of the limit state”. In addition it is stated that the selection of this value should be based on, among other factors, “the extent of the zone of ground governing the behavior of the geotechnical structure at the limit state being considered”. A statistical framework is presented to rationally assess the characteristic values according to Eurocode. Three statistical properties are required to quantify the characteristic shear strength values along a failure surface: the arithmetic mean, the variance and the scale of fluctuation. Simplified formulae for the determination of characteristic values are presented along with guidelines of typical input parameters. Stiff soils such as overconsolidated clays and clay shales exhibit brittle stress-strain behavior and are prone to progressive failures due to strain-softening. The shearing resistance first increases and then decreases with increasing displacements, and, as a result, the peak shear strengths of the materials at all points along a slip surface cannot be mobilized simultaneously. For these complex conditions, a pragmatic approach to estimate the characteristic values has been given. In addition, the apparently different definitions of characteristic values for construction materials such as concrete and soils have been presented and explained in a unified approach.
HSR University of Applied Sciences, Rapperswil, Switzerland