Examples of open caisson sinking in Scotland

Abstract

Open caisson-sinking techniques permit a shaft structure to be progressively sunk, either under its own weight or with the aid of caisson jacks, in a controlled manner from the surface to a predetermined depth. The technique is suited to shaft construction through weak soils, high- to extremely high-plasticity clays, silts, and sands and gravels, particularly below the water table. In the tunnelling and public works engineering sectors, open caissons are typically circular in cross-section; those used in harbour works are commonly square or rectangular in plan. The paper briefly describes the components and method of sinking dry and wet open caissons, highlighting good practice. It then examines in detail four recent, highly successful caisson-sinking operations carried out under a framework agreement for Scottish Water Solutions in their wastewater treatment works at Crianlarich, Doune, Killearn and Drymen. Although modest in size, each contractor-designed caisson was sunk through a variety of ground and water conditions, illustrating the versatility of the technique and its advantages over more conventional methods of shallow-depth shaft construction. The importance of a comprehensive site investigation programme and the control measures required to satisfy verticality and structural integrity requirements are discussed. The paper concludes with a series of practical guidelines designed to assist those contemplating using the technique, and to remind practitioners of good caisson-sinking practice.

Ground and Groundwater Responses Due to Shaft Excavation in Organic Soils

“…Pressure relief sumps, control valves as well as lined drainage materials were constructed at the shaft floor to control water seepage coming into the shaft as the base slab was deliberately designed not to cater for the full uplift forces. Similar to Allenby et al (2009), adequate shear resistance was provided between base slab and the caisson wall for further structural stability. Readings from water standpipes WS1 and WS2 in the vicinity also showed that groundwater did not drop more than 2 m during further construction works, as shown in Fig.…”

Cutting shoe design for open caissons in sand: influence on vertical bearing capacity

“…(a) Over-cut creation and support fluid delivery (Figure 3a): The over-cut is commonly formed by incorporating a steel cutting shoe around the leading edge of the caisson wall (e.g. Allenby et al, 2009;Sheil et al, 2018;Royston et al, 2020a), such as in Figure 4a, or by casting a thicker wall section at the base (e.g. Ter-Galustov et al, 1966;Nonveiller, 1987).…”

Settlement analysis of the giant open caisson during the construction of the Changtai Yangtze River Bridge

“…Open caissons have the advantage of good integrity, high structural stiffness, high bearing capacity, small deformation, and full utilization of internal space (Mu et al, 2015;Li et al, 2020). In recent years, they have been widely applied in deep foundations and underground structural engineering projects; they have become one of the main types of foundation in long-span bridge engineering projects (Allenby et al, 2009;Jiang et al, 2019).…”