ABSTRACT
According to Eurocode 7 the verification against hydraulic heave on the downstream side of a sheet pile wall must be fulfilled independent from the ground properties. The mechanism of hydraulic heave is based on the soil behaviour of non-cohesive soil, in which the upward directed seepage forces on the downstream side can cause liquefaction if the effective stress is reduced to zero. However, other failure mechanisms are expected in cohesive soil due to additional binding forces. Laboratory experiments have shown, that the alternative failure mechanism in cohesive soil is triggered by the formation of fractures at the foot of the sheet pile where high hydraulic gradients occur. To further investigate the mechanisms of these hydraulically induced fractures in cohesive soils, a new triaxial test has been developed, in which the pore water pressure in the centre of the specimen is increased until failure by fracturing occurs. The pore water pressure at fracture initiation, the fracturing pressure, is a measure for the soil resistance against hydraulic induced fractures. In an extensive laboratory study the influencing factors on the fracturing pressure have been determined by variation of the sampling material, the rate of the pore water pressure increase, the stress and drainage conditions. Further insight into the stress state at fracture initiation could be gained by numerical calculations. It could be concluded, that the failure by fracture differs significantly from the failure mechanisms in cohesionless soil. Therefore new concepts are required to ensure the safety against hydraulic failure.
