Performance-Based Design Concept of Soil for Seepage Failure within Cofferdam

Abstract

Safety design of soil within cofferdam is discussed from the viewpoint of performance-based design for seepage failure. The behavior of soil with respect to seepage failure is first described using test results under a two-dimensional condition (without excavation). The states of soil or three limit states of ultimate, damage and serviceability, are defined, and critical or boundary values describing these states are then given. It is concluded that:
(1) The critical hydraulic head difference for damage is given as the hydraulic head difference at the onset of deformation H_y. The value of H_y is equal to the theoretical critical hydraulic head difference H_PF which is calculated effectively using the Prismatic failure concept.
(2) The critical hydraulic head difference for ultimate level is given as the hydraulic head difference at failure H_f. The value of H_f is given as H_f=1.11 Hy from the test results under the two-dimensional condition (without excavation).
(3) The critical hydraulic head difference for safety construction against seepage failure Hs is given as (0.460-0.733) H_y according to Japanese standards.