Installation of Stiffened Caissons in Nonhomogeneous Clays: Fid-Bau Portal

Installation of Stiffened Caissons in Nonhomogeneous Clays

Zhou, Mi / Hossain, Muhammad Shazzad / Hu, Yuxia / Liu, Hanlong

A significant difference between predicted and measured installation resistance of stiffened suction caissons was identified due to the existing uncertainty regarding the mobilized soil-flow mechanisms. This paper describes an extensive investigation of stiffened-caisson penetration in nonhomogeneous clays undertaken through large deformation finite-element (LDFE) analysis to provide insight into the soil behavior during installation of a caisson. The soil-flow mechanisms around and between stiffeners, and inside and outside of the caisson, and the corresponding penetration resistances were presented from a parametric study, exploring a range of dimensionless parameters related to stiffened-caisson geometry, caisson roughness, and soil strength nonhomogeneity. The LDFE results were compared with centrifuge test data in terms of the soil-flow mechanisms and penetration resistance profile, with good agreement obtained. Three interesting features in the mobilized soil-flow mechanisms inside the caisson were observed: (1) soil started to infill the gap between the bottom two stiffeners when the bottom stiffener penetration reached $H_{r}$ ( $H_{r}$ is the critical depth of rotational soil flow around bottom stiffener); (2) soil started to infill the gap between the second and third bottom stiffeners when the second stiffener penetration reached $H_{c}$ ( $H_{c}$ is the critical depth of soil backflow into gaps above the 2nd stiffener); (3) profound soil heave due to significant inward flow and the presence of stiffeners and gap between stiffeners. Both $H_{r}$ and $H_{c}$ were shown to be a function of the stiffener-width to caisson-diameter ratio, normalized soil strength at the mudline, and soil strength nonhomogeneity. To predict the penetration resistance profile in the field, a rational analytical penetration model, based on the revealed soil-flow mechanisms, was proposed. The LDFE data were used to calibrate the model. Very good agreements were obtained when the proposed model was validated against measured data from field installation and centrifuge tests.