Impact of Anisotropy in Permeability of Peaty Soil on Deep Excavation

Abstract

Two case studies involving deep excavation in peaty soils are presented in this invited paper. The water and organic contents of peaty soils can be high as 1,200 and 60%, respectively. The design of deep excavation involving peaty soil layer can be very challenging as it is known that peaty soil can exhibit greater permeability in the horizontal direction than the vertical direction, hence the term anisotropy in permeability. If somehow ground water drawdown is triggered during deep excavation, the impact on nearby infrastructure can be detrimental as the kh:kv value can range between 2 and 10 with an average value of 5, as back-analysed in Case Study 1. Subsequently, by employing recharging wells as a form of ground remedial work, the excavation of a deep shaft was successfully carried out. In Case Study 2, ground improvement method via wet Deep Soil Mixing (DSM) technique was successfully employed to improve an underlying peaty soil layer with the hope that it could achieve slope stability and to provide an impermeable cut-off prior to carrying out the deep excavation work.