Excavation is usually employed in the construction of basement of buildings and underground space of the mass rapid transit and the subway system in urban areas. Braced excavation is a complicated soil-structure interaction problem and it is a challenge to engineers to simultaneously ensure the safety of excavation system as well as the integrity of properties adjacent to the excavation site including buildings, structures, and life pipes. In a routine excavation design, engineers usually pay much attention to reaching the safety requirements of excavation design, namely, the stability of excavation system. Many empirical, semi-empirical and numerical methods were developed for evaluating the stability of excavation. The past practical experiences indicated that the accuracy of the existing methods to evaluate the stability of  excavation is generally acceptable although the ground conditions at various excavation sites are non-homogeneous and have highly spatial variation. This may be attributed to the employment of a relatively conservative factor of safety in the stability analysis of excavation