Liquefaction and earthquakes

Soil liquefaction is a phenomenon in which soil loses much of its strength or stiffness, generally for no more than a few minutes, but nevertheless for long enough to make liquefaction the cause of many failures, deaths and major financial losses. 

The nature of the liquefaction is easy to understand soil particles re-arranging to denser state under a stress perturbation and causing excess pore water pressure to develop because of insufficient time for the displaced water to escape. The stress perturbations causing liquefaction are often earthquakes, but these are by no means the only cause. Storm wave loadings may be important with coastal/ offshore projects and liquefaction has been induced by vibration of machinery. Liquefaction can also be triggered statically, either by slope steepening or by increasing pore water pressures within the fill mass. 

Static liquefaction slides have also developed in quite dense sands (e.g. Fort Peck and Nerlerk) when those sands have experienced reducing mean stress in part of the slopes as the underlying foundation was displaced (yielded) horizontally because of the load static imposed by the fill sand behaviour under reducing mean stress is a current research interest (e.g. Chu et al, 2012) but the practical implication is straightforward consider possible foundation movement as well as the issues around the hydraulic fill itself. 

A wide range of soils are susceptible to liquefaction, certainly from clean sands through to non-plastic silts. Practically, this includes all soils likely to be used for hydraulic fills. 

Liquefaction studies in the framework of land reclamation are required to decide whether or not ground improvement will be necessary and, if so, to which minimum level. In general, this will be improvement of the fill material, but sometimes (static) liquefaction of the natural underlying soil also needs to be prevented. 

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