ABSTRACT
There are many underground construction projects, including tunnelling and deep excavations, in Singapore. However, the underground construction is challenging when encountering Singapore soft marine clay due to its poor engineering properties, such as low shear strength and stiffness. Cement stabilisation through deep mixing or jet grouting has been commonly used to treat the soft marine clay for underground construction in Singapore, which can significantly increase the shear strength and elastic modulus, as well as decrease the permeability of soft clay. However, the process of manufacturing traditional Portland cement (PC) leads to negative environmental impacts, e.g. high CO2 emissions and energy consumptions. In addition, the PC is not very effective for stabilisation of marine clay with high water content. Hence, this study proposes to use a novel sustainable binder consisting of two industry by-products, namely carbide slag (CS) and ground granulated blast furnace slag (GGBS), to stabilise Singapore soft marine clay for underground construction. By replacing PC with industry by-products, the associated environmental impacts are significantly reduced. Specimens of soft clay stabilised by both CS-GGBS and PC with two binder contents were prepared in laboratory and then tested at different curing ages. The key engineering properties related to underground construction, including unconfined compressive strength, elastic modulus and permeability of the stabilised clays with different binders were compared. The results indicate that the CS-GGBS-stabilised soft clay can achieve much higher unconfined compressive strength (up to ~300%) and elastic modulus (up to ~600%), and lower permeability (one order of magnitude) than the corresponding PC-stabilised soft clay, which are beneficial to the soft stabilisation for underground construction.
