توضیحات
ABSTRACT
Winkler model is one of the most popular models in determining the modulus of sub grade reaction. In this model, the sub grade soil is assumed to behave like infinite number of linear elastic springs. The stiffness of these springs is named as the modulus of sub grade reaction. This modulus is dependant to some parameters like soil type, size, shape, depth and type of foundation. The direct method for estimating the modulus of sub grade reaction is plate load test that is done with 30-100 cm diameter circular plate or equivalent rectangular plate. Afterward, we have to extrapolate the test value for exact foundation. In the practical design procedure, Terzaghi’s equation is usually used to determine the modulus of sub grade reaction for exact foundation, but there are some uncertainties in utilizing such equation. In this paper the size effect of foundation on sandy sub grade with use of finite element software (Plaxis 8.2) is proposed to investigate the validation of Terzaghi’s formula on determination of sub grade reaction modulus. Also the comparison between Vesic’s equation, Terzaghi’s one and obtained results are presented.
INTRODUCTION
Soil medium, because of the nonlinear, stress-dependant, anisotropic and heterogeneous nature, has very complex mechanical behavior. Hence, instead of modeling the subsoil in its three-dimensional nature, subgrade is replaced by a much simpler system, called a subgrade model that dates back to the nineteenth century. Searching on this concept leads to two basic approaches, which are Winkler approach and the elastic continuum model. Both of these models are of widespread use, both in theory and engineering practice. Winkler (1867) was assumed the soil medium as a system of identical but mutually independent, closely spaced, discrete and linearly elastic springs. The ratio between contact pressure (P) at any given point, and settlement (y) produced by load application at that point, is named the coefficient of subgrade reaction, Ks: Ks=p/y In fact, in this model subsoil is replaced by fictitious springs whose stiffness equals to Ks. However, the simplifying assumptions, which this approach is based on, cause some approximations. One of the basic limitations of it lies in the fact that this model cannot transmit the shear stresses, which are derived from the lack of spring coupling. In addition, linear stress-strain behavior is assumed. The coefficient of subgrade reaction, Ks, identifies the characteristics of foundation supporting and has a dimension of force per length cubed .
Year: 2011
Publisher : Sixth National Congress on Civil Engineering
By : M.Janbaz, S.Janbaz
File Information: English Language/ 7 Page / size: 181 KB
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سال : 1390
ناشر :ششمین کنـگره ملی مهنـدسی عمـران
کاری از : مسعودجانباز ,جانباز
اطلاعات فایل : زبان انگلیسی / 7 صفحه / حجم : KB 181
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