Diaphragm walls are commonly analyzed by 2D modeling techniques which rely on the plane strain behavior. The corner locations of the wall have a relatively high rigidity due to its constraining effect. At corners, wall can withstand high lateral earth pressures without excessive movements. The extent of the constraining effect of wall at corners cannot be well explained with 2D analysis. The corner effects are better explained in 3D analysis when compared to 2D approaches. The behavior of a 60 cm thick diaphragm wall in mixed soil conditions for a cantilever length wall of 6.2 m excavation is studied for both 2D and 3D approaches in this paper. 3D behavior of the wall is studied for isotropic and anisotropic conditions. Further, shape effects are also analyzed for two different excavation pit sizes. The effect of wall geometry (L × B) is considered in the 3D analysis. The outcome of the present study explains the variations in wall deflection near the corner and at the middle portions of the box in both 2D and 3D numerical modeling, for the cantilever portion of excavation. The numerical predictions are compared with the monitoring data that has been collected during the excavation phases. The performance of the wall deflection is compared at the corners and middle portions of the cantilever excavation. The results indicate that the deflection of the wall at the corner of the excavation pit is influenced by the corner effect. The deflection of the long-side diaphragm wall is observed to be larger than the short-side. It is concluded that the width of the pit plays an important role in the wall deflections. It is noticed that for a given aspect ratio, deflections increased with an increase in the width of the pit.