Performance-Based Design for Top-Down System in the Geotechnical Conditions of Qom, Iran

Rapid development in residential areas has increased substructure construction, which has become problematic in large cities. Deep excavation induces ground deformations such as lateral movement and vertical settlement in the soil mass adjacent to the excavated site. Adjacent structures and infrastructures necessitate the use of an efficient design method for urban excavation stabilization to restrict the magnitude of ground deformation. Stress-based design for excavation stabilization does not provide sufficient information about the ground deformation and the probable damage to adjacent buildings. The current study endeavored to attain performance-based design by considering top-down construction in the geotechnical conditions of the city of Qom in Iran. Geodetic surveys were applied to monitor field performance using total station TS02. The deviations of gathered data found to be about 3 mm and 3.8 mm which are within monitoring tool accuracy. A numerical model could be calibrated using the result of geodetic studies. By dividing the geotechnical conditions into four geotechnical types and taking the structural elements as variables in the calibrated model, exponential graphs could be drawn to facilitate the design of excavation support systems on the basis of performance. The numerical studies indicated that the Qc-2 layer shows the least pliability of the structural variables because of its inherent stability. The resulting graphs are able to determine the required stiffness of the excavation support systems based on the maximum allowable deformation of adjacent structures under specific geotechnical conditions.