Effect of depth-dependent permeability of sand plug on suction caisson installation

The suction-assisted caisson installation in sand must be designed based on the required and the critical suction pressure. The inaccurate prediction of the suction pressure will lead to the obstruction of the installation. In this paper, the effect of depth-dependent permeability is considered. The new simplify prediction method of the required and critical suction pressure is developed by laboratory model tests and analysis, based on the framework proposed by Houlsby and Byrne (Geotech Eng 158: 135–144, 2005). In the model tests, the volume and permeability of sand plug inside the caisson were measured and found varies with suction-assisted penetration depth. To consider model size effect, suction caisson models with various dimensions were used in the penetration tests and together with sand beds of three different relative densities. The current 1-g model tests results were combined with published high-g centrifuge tests data to eliminate stress effect. The new prediction formula of the depth-dependent permeability of sand plug inside the caisson was developed including the stress effect. This depth-dependent permeability formula was applied in the development of the prediction formulas to estimate the required and critical suction pressures during the suction installation. The suction pressure formulas were validated against existing field data and showed improved predictions as the depth-dependent permeability was considered. Comparing to the framework proposed by Houlsby and Byrne (Geotech Eng 158: 135–144, 2005), it is helpful to improve the prediction accuracy to a certain extent, in our case approximately by 25%. Therefore, the newly developed suction pressure formula can be used in practical designs for more refinement.