Selection of characteristic values of spatially variable cement-treated clays for deep excavations

Cement-treated soils (CTSs) are commonly used to improve in situ soft clays. However, properties of CTS are often highly variable, posing significant challenges in the analysis and design of geosystems. This paper proposed a framework to determine the characteristic strength and stiffness parameter values for the design of CTS slabs in deep excavations under two typical modes of failure, while considering spatial variabilities. First, the proposed framework provided a series of charts for engineers to select the characteristic strength and stiffness parameter values of CTS. A comprehensive set of in situ test results from a Singapore site is then used to create a database of the statistical and spatial variabilities of CTS. Finally, a deep excavation case study in Singapore is used to illustrate the proposed charts. The results show that the characteristic strength value of CTS can range from 25% to 70% of the mean value depending on the magnitude of the statistical and spatial variabilities and the geometry of the CTS slab. Through a comparison with national design codes, the proposed framework is demonstrated to provide to a more rational selection of characteristic parameter values, leading to a more economical design of CTS slabs in deep excavations.