In Norway, deep excavations in soft marine clays are usually supported by sheet pile walls (SPW) and tieback anchors or internal struts to safeguard the building pit and its surroundings until sufficient support is provided by the permanent structure. Often, soil stabilisation by the Dry Deep Soil Mixing (DDSM) method are also used to improve the strength and stiffness properties of the soft clays within the excavation pits, to both increase the global stability against failure and reduce displacements on the retaining structure. Measures like soil stabilisation, the installation of tieback anchors and internal struts are both expensive and time consuming and can increase the greenhouse gas emissions of a project significantly.
An alternative to SPW supported by anchors or struts is to use cantilever SPW for excavations up to medium depths. The method has seen an increased use in soft to medium stiff clays in Norway recent years, but their system behaviour has not been studied sufficiently previously. The cantilevered SPW is related to uncertainties in terms of the wall displacements governed by design assumptions regarding the earth pressures and performance of the soil stabilization over time. However, the system shows a big potential of saving project costs, shorten the excavation time and reducing the carbon footprint as cost and time-consuming anchorage work is not required.
The cantilever sheet pile walls are instrumented and monitored closely throughout the entire construction process. The monitoring includes fibre optic strain sensors on the SPW, inclinometers, load cells on temporary struts and geodetic surveying points on the SPW. The work package will analyse the monitoring data to gain new knowledge on the design of support structures and focus on the earth pressure distribution along the sheet pile wall and its deformation (displacement) during different stages of the excavation. Based on the measurements as well as (analytical and numerical) back-calculations, design procedures will be proposed for cantilever sheet pile walls.
