Performance and Load Distribution in Lime-Cement Stabilized Soil as Support for Deep Supported Excavation in Marine Clay

Urban development and progressive growth of the construction industry requires geotechnical activities under difficult conditions, such as sensitive marine clays. Ground improvement by lime-cement stabilization (LCS) is often used to achieve the required safety level and to reduce deformations on support walls for deep excavations in these conditions. Despite previous studies and research on LCS, there are still uncertainties on the quality, performance and load distribution in the stabilized soil volume which influences the design of such excavations. The soil-structure interaction and consequently also the deflection profile, is often difficult to predict. The research project CURIOUS (Campus Ullevål: Research and Instrumentation Of Underground Structures) was initiated at NGI to further study and improve the design of deep excavations in sensitive marine clays supported by sheet pile walls (SPW) and LCS. A six-meter-deep excavation pit in Oslo was equipped with an enhanced monitoring system to gain a better understanding of the performance of the SPW and the stabilized soil during the different construction stages. The monitoring included strain sensors and inclinometers on the SPW, inclinometers in the stabilized soil in the excavation pit, load cells on temporary struts and geodetic points on the SPW. The paper presents results of the monitored deflections in the SPW and deformations of the stabilized soil volume and assess the performance of the LCS soil during the excavation. The results are compared with the numerical design analyses in 2D and 3D finite element analyses and subsequently used to propose enhanced design procedures for deep excavations supported by SPW and LCS.