Madanayaka, Thushara, Sivakugan, Siva, and Ameratunga, Jay (2017) Validity of the method of fragments for seepage analysis in double-wall cofferdams. In: Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering. TC213. pp. 2921-2924. From: ICSMGE 2017: 19th International Conference on Soil Mechanics and Geotechnical Engineering, 17-22 September 2017, Seoul, South Korea.

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Abstract

The method of fragments is a simple analytical technique for solving confined seepage problems. Design charts for determining the flow rate and exit gradient, have been proposed in literature for a double-wall cofferdam. The accuracy of the above method depends on the assumption that equipotential line at the tip of the cut-off wall is vertical, dividing the flow domain into two fragments. This paper discusses the validity of this assumption, and its effect on the accuracy of the solutions. Extensive numerical simulations were conducted by varying the cofferdam width (2L), embedded depth of the cut-off wall (s) and excavation depth (αs) with a constant height of the soil domain (T). Numerical simulations show that the equipotential lines at the tip of the cut-off wall are far from vertical for low values of L/T and s/T ratios and become closer to the vertical with increasing values of L/T and s/T. Also the values of flow rate and exit gradient estimated from the method of fragments become very close to the values computed from the full numerical solutions when increasing the values of L/T and s/T. Nevertheless, for low values of L/T and s/T, estimates from the method of fragments are on the conservative side and are still within acceptable limits.

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