Seismic-Liquefaction Assessment Methods In Conjunction With Pore Pressure Development And Dissipation

The assessment of potential liquefaction on the performance of a given structure requires assessment of sitespecific factors with a certain degree of accuracy. In sensitive or high-hazard structures, such as dams, extreme seismic events are to be considered (ANCOLD, 1998), such as those with a return period in excess of 30,000 years compared with typical return period of 452 years for buildings.

Although site-specific earthquake parameters may be assessed by a seismologist for bedrock conditions, the seismic wave may be either attenuated or amplified by the overlying soil profile to a dam foundation. Liquefaction may be generated by transient pore pressures as the soil particles try to re-arrange themselves in a denser packing. Given the characteristics of the foundation hydrogeology and nature of the earthquake, concurrent dissipation of the generated pore pressures may occur, thus mitigating the consequences. Despite the recognition of potential benefits, in most cases undrained conditions are assumed (ANCOLD, 1998).

The authors present a methodology suitable for practical applications. A seismic ground response analysis, based on total stress approach, will be carried out in conjunction with a transient seepage analysis in the time domain. The analysed soil profile consists of an 11 m thick layered deposit of saturated clay, silt and sand overlaying a siltstone. Effects of liquefaction in the upper sand layer, as well as pore pressure development and dissipation, will be assessed.