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| Discussion on the shape effect and equivalent diameter of prefabricated vertical drains |
| HUANG Chaoxuan, ZHANG Yongjin, YU Jindi |
| (Zhejiang Design Institute of Water Conservancy and Hydroelectric Power, Hangzhou, Zhejiang 310002, China) |
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Abstract In view of the shortcomings of the round-shaped drain approximation method for the consolidation of PVD (prefabricated vertical drain), this study presents the ribbon PVD as an equivalent to a flat elliptical cylinder with a more compact shape. The analytical solution for the consolidation of the elliptical cylinder considering the influence of vertical consolidation is provided, along with a more concise calculation formula for the dimensionless parameter Fh, derived using the symbolic deduction module of Matlab. The rationality of this approach is validated through engineering case studies, which suggest that the dimensionless parameter Fh reflects the average radial drainage distance of the PVD foundation. According to the analytical solution of elliptical cylinder consolidation, it is posited that, with a fixed width b and thickness δ of the PVD, the equivalent diameter dw is positively correlated with the diameter of a single drain de. When the diameter of the single drain is sufficiently large (e.g., de/b≥10), the equivalent diameter stabilizes. The formula for calculating the equivalent diameter of conventional size PVDs is given as, with the average consolidation error ?U of the soil foundation generally being less than 1% when this formula is applied. Conversely, when the relative diameter of a single drain de/b is smaller, the equivalent diameter is less than the value predicted by the aforementioned formula due to shape effects. If the equivalent diameter continues to be used under these circumstances, the drainage and consolidation rates of the soil foundation may be overestimated. Therefore, in the actual design of projects and indoor model tests, it is essential to consider the influence of the shape effect of PVDs.
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2025, Vol. 44 
