Effects of using concrete pre-supporting systems with NATM in construction of underground stations

The soil in egypt and especially in cairo city is mostly soft soil varying between clay and sand layers. excavation of large span (more than 10 meter) underground station in such soil layers can cause large displacements (more than 30 mm) which may result in harmful effects for the nearby buildings which are often located within distance from the center line of station equal to 1.5 times of total width of station. therefore,the excavation process of large span underground stations needs a supporting system to enable redistribution of the loads and stresses around the excavation opening to the surrounding soil mass to avoid undesirable excessive displacements. this paper shows how the concrete pre-supporting system can be used to control the stability of the underground space and the ground settlement. numerical modeling is used to simulate all the construction stages and to analyze the ground behavior. analysis results from different models show that pre-supporting systems can be used successfully to reduce the ground surface settlement and to enhance ground stability.