Detemination of Parameters for The Tangent Modulus Approach

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Addis Ababa University


The estimation of settlement often receive less attention than they deserve (or even not at all), with the result that excessive settlements cause far more problem than do bearing capacity failures. Settlement analysis is therefore one of the two most important types of analysis made by soil engineer for designing safe and economical structures. This paper introduces different method for the determination of settlement, which is known as the tangent modulus approach, this approach deals with the use of a coherent definition of compression modulus leading to a unified procedure of practical settlement calculation for different types of soils ranging from rocks to very soft soil. In this approach a compression modulus, the tangent to stress Vs strain curves obtained from laboratory tests play a significant role. It is a measure of the resistance of soil against deformation due to application of loading. The compression modulus describes the resistance of the media or an isolated part of it against a forced change of equilibrium conditions. The resistance concept is very well developed in other field of engineering except its application for settlement analysis in soil mechanics is new. The procedure is therefore believed to give a much clearer mechanical understanding of what volumetric soil compression actually is. Moreover, the use of classical concepts have lead to a simpler, and more straight forward calculation procedure, where the practical advantage are most apparent when applied to layered soils. Even though the classical approach for determining the consolidation settlement suggested by Karl Terzagi has contributed more for the development of settlement computations, it has its limitations in that it assumes the value of the compression modulus to be constant, which is true only for elastic material. Further more, it was believed it is the initial pore water pressure that describes the consolidation characteristics of thick clay layer. But it is shown here in that a new theory for stress distribution, compatible with the actual soil properties is included; moreover, it is shown that the calculation of the time rate of consolidation of clay has to be based on strain distribution, instead of pore pressure distribution, to avoid fundamental misunderstandings. It is therefore the application of this tangent modulus approach by introducing and fixing parameters for Addis Ababa clay soils that this paper introduces.



Modulus ;Approach