Deformation-Based Limit States for Earth Embankments

Traditional design approaches based on the concept of factor of safety do not provide a complete indicator of level of safety pertinent to earth structures given uncertainties in loading, soil properties, and changes in geometry that can take place with time. Thus, there has been a tendency to utilize probabilistic analysis in addition to conventional design methods. Work is presented herein to introduce limit states, based on numerical modeling in conjunction with probabilistic analysis, for water holding embankments and flood protection structures. An embankment dam was modeled using coupled flow/deformation analysis to capture the interdependency of under-seepage and through-seepage with deformation associated with the development of plastic zones and shear bands. Limit states were defined in terms of deformations and seepage gradients that correspond to levels of performance or extent of damage in the embankment. The analysis showed as the water level increased in the reservoir, lateral displacement also increased and zones with high seepage velocity emerged at the entrance and exit locations of the dam. Depending on the statistical variation of input parameters, probabilities of exceeding limit states are calculated and presented for the case study. As water rises in the pool, the probability of exceeding each limit state increased and the target deformation was changed to the next limit state.