Analytical Solution of Consolidation of the Composite Foundation Reinforced by Stone Columns Combined with Vertical Drains

Composite foundations reinforced by stone columns and vertical drains are widely utilized in various projects due to their low cost, high consolidation rate, and effective reinforcement. Although the consolidation theory of a single vertical drain or stone column composite foundation is well-developed, reports on theories involving both types of drainage bodies are scarce. Previous models only accounted for unidirectional seepage of pore water in the radial direction, which diverges from the actual situation. Therefore, a theoretical model that accounts for bidirectional seepage of pore water under external loading in the radial direction is proposed. This model features a permeable top and an impermeable bottom, and the analytical solution is derived from the seepage continuity conditions of the stone columns, vertical drains, and surrounding soils. Under certain conditions, this solution may be simplified to the consolidation models for foundations with either a single stone column or a vertical drain, thereby demonstrating the universality and accuracy of the approach. Subsequently, the solution is applied to the settlement calculations of both an actual project and an indoor model test, with results aligning well with the measured data. The analytical solution is further employed to investigate the consolidation behavior of the composite foundation in detail. The results indicated that the consolidation rate significantly benefits from the installation of vertical drains between stone columns. Besides, the consolidation rate increases with the number of vertical drains, and the permeability coefficient of these drains greatly influences both the consolidation and settlement rates. Compared to reducing the column spacing in classical composite foundation technology, installing vertical drains between stone columns has higher economic value. © 2024 Sichuan University. All rights reserved.