This example demonstrates the use of PLAXIS 3D for designing a deep excavation required for the construction of a new building located adjacent to an existing structure. The primary focus is to evaluate the forces developing in the diaphragm wall and propping system, the ground deformations, and their impact on the existing building—particularly on its piled-raft foundation.

The excavation pit has an L-shaped configuration, consisting of two contiguous rectangular areas. The larger measures 10 m × 9 m, and the smaller 7.5 m × 4.7 m. The total excavation depth is 14 m. This excavation is positioned 4 m from an existing 19-storey building, which is also included in the model. The retaining system consists of a 0.8 m thick and 21 m long diaphragm wall, supported by three levels of horizontal struts located at depths of -2 m, -6.5 m, and -9 m.

The excavation will be achieved in 4 steps going through depth respectively equals to -2 m, -6.5m, -9m and -14m. Prior to excavating the upper clay layer, dewatering will be done using wick drains in combination with pumping well.

The document will detail the complete model construction and analysis setup, starting with an undrained analysis, including comprehensive post-processing of the results. This initial phase will emphasize the development of suction and excess pore water pressures behind the wall. A second phase will revisit the same scenario using consolidation analysis, to assess the effect of pore pressure dissipation throughout the excavation process.