Investigation of soil-structure interaction for large diameter caissons

Thesis

Large diameter open caissons are widely adopted in civil engineering infrastructure projects for deep foundations, underground storage and attenuation tanks, pumping stations, and launch and reception shafts for tunnel boring machines. These structures are commonly formed using cast in place reinforced concrete, with the structural self-weight in combination with soil excavation within the caisson, forcing the caisson continuously into the ground. This sinking process presents several engineering challenges for engineers, including maintenance of caisson verticality, control of the rate of caisson sinking, and minimisation of soil-structure frictional stresses through the use of lubricating fluids.

Controlled sinking of caissons requires a thorough understanding of the interaction between the caisson shaft and the surrounding soil, as well as the bearing capacity at the base of the caisson. New understanding has been developed by instrumenting a number of caisson shafts, on live construction sites, for the measurement of soil-structure interaction stresses, structural performance and caisson movements. All data was processed in real-time and displayed to the site construction team via wireless technology, giving the team control over the construction process and allowing them to respond rapidly to adverse responses. This unique set of field data provides new insight into soil-structure interaction stresses, lubrication and structural performance, as well as caisson movements in varying ground conditions.

Bearing capacity beneath the tapered face at the base of the wall was explored through experimental testing and numerical modelling. A simplified closed-form design method for the prediction of the bearing capacity of a sloped footing in clay is established, with insight into the bearing failure mechanisms in both sand and clay also established. The design methods are validated against the monitored data from the field projects as well as small-scale laboratory testing.

Authors: Royston, R

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford