Modified Equivalent Plane-Strain Model on Consolidation of Soft Ground Improved by Preloading with PVDs

Key words:  consolidation  prefabricated vertical drains  plane-strain model  vacuum preloading  lateral deformation

Abstract:

The combination of vacuum preloading and Prefabricated Vertical Drains (PVDs) has been widely used in coastal engineering projects to improve large-scale soft ground. Nevertheless, more precise theoretical models are still desperately needed, to meet the increasingly stringent deformation design specifications. To refine the numerical simulation of the soft ground improved by PVDs, a modified plane-strain equivalent model is proposed by incorporating the shape effect of PVDs based on the permeability matching method. The model is then validated through comparisons with a single-drain analytical model, a realistic 3D finite element model, and measured data from a field case history. The case analysis indicates that the surrounding soil adjacent to the treated zone is also influenced by vacuum pressure and predominantly exhibits lateral displacement during preloading. The lateral displacement in the surrounding soil without PVDs decreases with depth, with the maximum value at the soil surface occurring near the edges of the treated zone. The parametric analyses suggest that, under identical total load magnitudes, reducing the surcharge load and/or the loading rate can effectively decrease outward displacements of the surrounding soil. In practical ground improvement, the implementation of an optimal combined vacuum and surcharge preloading is shown to be effective in mitigating the adverse impacts of lateral displacements on adjacent environments.