Laboratory investigation of cemented silt improved with bentonite and phosphogypsum in DCM walls

Abstract

Engineering properties of cemented soil in deep cement mixing (DCM) walls significantly affect security and stability of foundation pit, especially in regions where silty and sandy layers are widely distributed. This article investigates properties of cemented silt improved with calcium bentonite and phosphogypsum, in order to realise economic and environmental benefits. A series of laboratory tests, including unconfined compression strength (UCS) tests, hydraulic conductivity tests and scanning electron microscope (SEM) tests are carried out to examine strength, deformation, hydraulic behaviour and microstructure of solidified silt. The results show that the growth of unconfined compressive strength is as high as 86 ∼ 166 per cent with the addition of optimal content of calcium bentonite and phosphogypsum. The hydraulic conductivity of cemented silt decreases by one to two orders of magnitude with increasing additives and curing time. Moreover, the SEM pictures account for the existence of an optimal content of phosphogypsum explicitly. The microstructure of specimens reflected by SEM pictures shows a high consistency with UCS tests and hydraulic conductivity tests. Laboratory tests and cost analysis indicate that calcium bentonite and phosphogypsum have potential applications as binders in construction of DCM walls.