Towards a complete model of soil liquefaction: the importance of fluid flow and grain motion

Abstract

When loosely packed water-saturated granular soils, for example sands, are subjected to strong earthquake shaking, they may liquefy, causing large deformations with great destructive power. The phenomenon is quite general and occurs in any fluid-saturated granular material and is a consequence of the transfer of stress from inter-grain contacts to water pressure. In modern geotechnical practice, soil liquefaction is commonly considered to be an ‘undrained’ phenomenon; pressure is thought to be generated because earthquake deformations are too quick to allow fluid flow, which enables water depressurization. Here, we show via a first principles analysis that liquefaction is not a strictly undrained process; and, in fact, it is the interplay between grain rearrangement, fluid migration and changes in permeability, which causes the loss of strength observed in so many destructive earthquake events around the world. The results call into question many of the common laboratory and field methods of evaluating the liquefaction resistance of soil and indicate new directions for the field, laboratory and scale-model study of this important phenomenon.

Post-liquefaction reconsolidation of sand

“…Changes in entropy due to heat generation are typically neglected for sands. Without the term for entropy, the simplified equation of [5] is equivalent to other consolidation equations used in geophysics (e.g. [4,22]).…”

“…Darcy's law is considered valid, at least in the case of earthquake-induced liquefaction [6]. Based on these assumptions, a complete model for liquefaction is given in [5]. After dropping terms that are related to the compressibility of the fluid, which is not expected to be of importance for homogeneous sand layers, a simplified equation is also proposed in [5].…”

“…Based on these assumptions, a complete model for liquefaction is given in [5]. After dropping terms that are related to the compressibility of the fluid, which is not expected to be of importance for homogeneous sand layers, a simplified equation is also proposed in [5]. The terms of this simplified equation include the temporal change of pressure, the temporal change of porosity, the spacial gradient of Darcy's velocity and the temporal change of entropy.…”

“…They are used for an array of problems, from the estimation of excess pore pressure generation on the onset of liquefaction (e.g. [4,5]), to the evaluation of the behaviour of sediment suspensions (e.g. [20,21]) and to the assessment of seabed response to wave loading (e.g.…”

Investigation of Aqueous and Non-Aqueous Phase Liquids Migration in Fractured Double-Porosity Soil

“…According to Sa'ari et al [7], the double-porosity soils have different hydraulic properties of two sub-region media due to different pore size characteristics. Existing research by Lakeland et al [8] had demonstrated that liquefaction is not a strictly undrained process via first principles analysis, but in fact observation of numerous earthquake events shows that the interplay between soil rearrangement, liquid migration, and permeability changes have led to loss of strength. The fracture porosity formation were characterized by water-bearing formations where groundwater flows along the fracture solid nd 2017, Surabaya -Indonesia rock, while a fracture is created as rock mass is broken down due to tectonic force [9].…”