Excavation Support System Design Method to Limit Damage in Adjacent Infrastructure

A major concern for urban construction projects involving deep excavations is the impact of excavation-related ground movements on adjacent buildings and utilities. Consequently, stiff excavation support systems are required to execute the work. The conventional approach for designing an excavation support system is to use a limit equilibrium approach to determine the required capacity and stiffness of the excavation support system. Although this approach may provide an adequate factor of safety against structural failure, it may yield excessive system deformations and subsequent ground movements, causing nearby structures to possibly sustain damage. Thus, it is critical that design methods for excavation support systems consider the potential of induced damage in adjacent infrastructure. Current methods that consider potential damage to adjacent structures in the excavation support system design compare predicted damage to acceptable damage at the end of the support system design process. These design methodologies involve iterations of the support system characteristics until the required stiffness of the system complies with the acceptable level of damage. Any variation in the ground or adjacent structure characteristics from a previous definition may cause a complete redefinition of the support system characteristics. This paper presents a new design methodology that directly designs an excavation support system by first considering an acceptable level of damage in the surrounding facilities and estimating the corresponding ground deformations. The wall and support elements of the support system are then designed such that the system yields the limiting ground deformations. The resulting excavation support system limits damage to adjacent structures below an acceptable level and automatically satisfies the structural stability requirements. More significantly, the design of the excavation support system does not require an iterative process.