Abstract

Roads constitute the largest and most expensive project governments undertake. The deterioration of the infrastructure of these roads represents a major and outstanding problem in transportation engineering. Construction of roads is usually made by stripping the top soil (600 to 1000 mm), which often contains organic materials, and replacing it with a layer of subgrade material (crushed stones, well-graded sand). A thin layer of asphalt or concrete is usually placed on the top of the subgrade layer to provide a durable surface. This thesis examines the role of a deep deposit on the compression of the overlain subgrade layer. The object of this study is to provide a practical method of analysis for the design of airport runways. The cross-anisotropic elastic body that is characterized by three independent elastic constant with a plane of isotropy is suggested as an improved mathematical model of natural soil deposit. The theory of stresses and displacements in a two-layer system is presented in accordance with the theory of elasticity. The theory present herein reveals the controlling influence of two important ratios on the load-settlement characteristics of the "two-layer system," namely; the ratio of the thickness of the upper layer to the radius of the bearing area and the ratio of the modulus of the deposit to that of the upper layer. For practical design purposes, the theoretical results of settlement and compression of the upper layer have been evaluated numerically and expressed in basic influence curves, for rough and smooth interfaces at the center and the edge of the load. These influence curves are made for a various combination of anisotropic and isotropic two-layer system. The influence curves of the compression of a thin layer overlying deep deposit, confirm that the stiffness of the lower layer has a significant influence on the compression of the upper layer.