THE PHYSICS AND MECHANICS OF LIQUEFACTION

Simple physics and mechanics are used to explain the first order shape, structure and distribution of surface and sub-surface liquefaction features. We relate basic models to field observations, assuming Newtonian fluids, low Reynolds’s number flow, cylindrical dikes and Mohr-Coulomb failure. An analytical solution demonstrates that pore pressure required for rupture of top soil and surface manifestation is linearly related to shear strength and thickness of the soil cap. It also shows that less initial pressure is required to reactive a pre-existing dike than to create a new one. The rate of dissipation of pore pressure in the liquefied layer also depends on properties of the overlying non-liquefied layer. Equations for ideal dike geometry show how changing parameters such as depth of water table, size and angularity of soil particles affect the volume of liquefaction. Volume per unit time is proportional to the fourth power of radius of dike. Fluid velocity profile is used to explain morphology of dike and grain size distribution with distance from wall of the dike. Recurrent liquefaction is discussed at two time scales. Elevated pore fluid pressures are shown to increase liquefaction susceptibility during aftershocks, while subsequent burial and compaction is shown to decrease susceptibility using porosity-depth exponential model. Implications for paleoseismic studies are discussed in brief. Observations of liquefaction features from Canterbury Earthquake Sequence 2010-2011 are compared with results of these simple models. These models give interesting, previously unexplored insights and show how undergraduate students, without the use of advanced tools, can design and lead targeted projects to brace niches that need to be addressed.