Soft ground tunnelling in Egypt: Geotechnical challenges and expectations

Abstract

Several large projects of tunnels and underground structures were executed in Egypt during the past 15 years. It is expected that these specialized construction activities will continue at similar rate during the next ten years to complete the existing plans of new infrastructures. Furthermore, the growing solidarity to improve, or at least maintain, the quality of urban environment will require moving more services below ground surface in the near future. For instance, more active utilization of underground space is badly needed for solving traffic problems and for expanding the limited available space for car parking within the congested urban areas. The majority of recently completed underground developments in Egypt were built through water bearing soft ground. For underground works, these subsurface conditions are considered problematic. Design guidelines and construction specifications of most of these tunnels and underground structures also demand preserving the surrounding buildings and other structures. Hence, several new construction technologies had to be utilized, for the first time in Egypt, to deal with these difficult tasks and constrains. Extensive studies have been conducted before and during the implementation of these subsurface projects. The methodology of coupling in-situ monitoring programs with sophisticated numerical modelling proved to be the most realistic scientific approach to document the geotechnical performance of these projects. The compiled results from these studies have provided a reliable base for detailed quantitative assessment of various construction techniques under the existing subsurface conditions. In this contribution, some of the main findings of the studies performed on recent soft ground tunnelling projects in Egypt are presented. The discussion is focused on some of the challenges facing geotechnical engineers during the implementation of these specialized projects in Egypt. Recommendations for the needed improvements in the currently used design tools and construction techniques are also offered.