Interaction between shallow foundations and unlined soft ground tunnels

The rapid growth in urban development has resulted in an increased demand for underground construction of water supply, sewage disposal, and transportation systems. Potential structural damage due to these tunneling activities under existing structures has long been recognized as a major problem to geotechnical engineers. Despite the continued research on this subject problem, there is no widely accepted methodology available at the present time which will lead to a safe and economical design of a foundation/tunnel system. Thus, this research was undertaken with the aim of developing a methodology for use in geotechnical profession.; The ultimate goal of this research was to develop an analysis/design methodology for shallow foundations subjected to a vertical central loading and underlain by unlined soft ground tunnels. The desired analysis/design methodology consisted of the equations for determinations of the extent of influence zone and the ultimate bearing capacity. To meet this goal, a three-dimensional elasto-plastic finite element computer program capable of handling the nonlinearity of soil behavior was developed and a wide range of boundary conditions was analyzed.; The mechanistic behavior of the foundation system analyzed was evaluated using the results of finite element analysis. Among the behaviors investigated were footing pressure vs. settlement relation, footing pressure vs. yielded area relation, propagation of plastic yielding, deformed configuration of tunnel, and stress distribution in the foundation soil mass and the tunnel periphery. From these data, the ultimate bearing capacity values for a wide range of boundary conditions were determined. These ultimate bearing capacity data were then used to formulate semi-empirical equations for determinations of influence zone and the ultimate bearing capacity. The effectiveness of the developed equations was illustrated by comparing the data obtained from the computer analysis with those computed with the equations, and a good agreement was obtained between the two sets of data. Therefore, it was concluded that the developed equations can be effectively used for practical applications at least within the conditions investigated. Additionally, recommendations were made for further study so that a more general methodology can be developed.