Review of D Wall Trench Stability for an Underground Metro Shaft Based on Analytical, 2D and 3D Numerical Methods

To facilitate underground metro excavation Diaphragm Walls (also called as D walls) are generally constructed as a temporary or permanent earth retaining system. After guide wall construction the first stage of D Wall construction involves excavation and simultaneous filling of slurry fluid. Several D Wall trench instability issues are quite common at this stage which may lead to cave in or collapse of D Wall trench. Several analysis methods are available to study this stability mechanism of D Wall trench. The trench parameters such as required slurry height above the ground water table, required slurry unit weight can be estimated by these methods. Also, trench stability can be ensured by determining the factor of safety from these methods. In this current study, the design of D Wall Trench is carried out by analytical and numerical methods. D Wall construction for an underground metro shaft is considered for the study. The shaft is in challenging geological condition such as presence of thick deep clay deposits and high ground water table. The D wall trench design is carried out by various analytical methods and is compared with two dimensional (2D) and three dimensional (3D) finite element methods. Plaxis 2D and Plaxis 3D, finite element-based software, are used for this purpose. Based on the results from both analytical and numerical methods, an optimistic trench parameter such as slurry height and slurry unit weight can be determined which can be compared with field observations.