Optimization of retaining wall in deep excavation for basement work

Deep basement construction always anticipated in urban areas especially in Kuala Lumpur where the area is dense and limited. The design of basement retaining wall and its support system involves careful analysis, design and monitoring system. This is due to the sensitivity of ground movement that can cause damage to the adjacent buildings, roads, utilities and others. The focus in this paper is to model the actual cases on site by using Finite Element Software (Plaxis2D). The result will be compared to obtain the best option and worth to consider. An actual site in Kuala Lumpur has been chosen for this study. All the relevant data were obtained and re-analysed. The site is located in Kenny Hill formation which is basically a completely decomposed rock and generally has the consistency of a clayey SILT soil. The presence of ground water level at shallow depth requires a suitable wall to be adopted. Thus, diaphragm wall and contiguous bored pile has been adopted in the analysis. Bottom up construction sequence is found to be more suitable compared to cantilever construction due to depth of excavation. Both type of wall has been analysed in Plaxis2D as plain strain model. However, geometry conversion is needed for CBP so that it can be modelled as plain strain instead of asymmetry model. The Hardening soil model is found to be suitable for analysis after making comparison between Mohr Coulomb model which overestimate the shear strength of soil. Result of lateral wall deflection from both types of walls shows the relationship between system stiffness and deflection of wall. A higher stiffness wall will result in less deflection. Thus, the main factor to select the suitable wall is not the system stiffness. However it depends on working space for construction, cost, embedment length etc