Two-Layer System - Burmister Theory

Forty years after the development of Boussinesq s analysis, Westergaard (1926) developed his own analysis for the determination of stresses in a two-layer system, where the first layer consisted of a concrete slab. Even though this theory did not cover the case of flexible pavements, it triggered the development of analysis for flexible pavements with two layers. 

Burmister (1943, 1945) was amongst the first researchers who developed theories on the determination of stresses and strains in flexible pavements. Other researchers, such as Hank and Scrivner (1948), Huang (1969) and Jelinek and Ranke (1970), also followed. 

The theories/analyses for determining the stresses in a two-layer system developed were based on certain assumptions/prerequisites. These were the following (a) the material of each layer is considered to be elastic, homogeneous and isotropic (b) the first layer has infinite dimension in the horizontal level and finite dimension in the vertical level (c) the second layer (subgrade) has infinite dimensions in both horizontal and vertical levels (d) the upper surface of the first layer is not subject to any other horizontal or vertical loading, except the traffic loading and (e) the first layer has a modulus of elasticity higher than or equal to that of the second layer. 

It should be mentioned that the above assumptions were also used for theories/analyses for determining the stresses in three or more layer systems. 

The numbering of the layers always begins from top to bottom. Thus, all properties bear the number T , for the first layer and so forth. In order to determine the precise interface level, the letters u (for under) and o (for over) were used. The letter u indicates the bottom surface of the layer, whereas the letter o indicates its upper surface. Thus, for instance, the designation, refers to the horizontal radial tensile stress developed at the bottom surface of the first layer. The same principle is also followed for systems with three or more layers. 

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