The extension of the underground and infrastructure projects in urban areas is often linked with the design and construction of complex geotechnical structures. Deep excavations are required to meet the demand, and in many cases, excavation sites are in close proximity to existing structures and facilities. A major concern in these excavations is to control the lateral wall deflections and the ground surface settlements. As a result, understanding and being able to predict the performance of deep excavations is an important issue for geotechnical engineers. A 3D numerical analysis can be valuable to assess the behavior of the earth-retaining structure and the surrounding soil. In this research, the main objective is to study the combined influence of the geometric configuration and the consistency of the cohesive soil on the performance of the diaphragm walls and surrounding soil under static and seismic conditions. This study comprises 3D numerical analyses performed for different configurations of deep excavation in cohesive soil supported by diaphragm wall. The results present the main impacts of the investigated parameters on the behavior of the earth-retaining structure under static and seismic conditions.