Volume Contraction in Shallow Sediments: Discrete Element Simulation

Abstract

Displacements induced by mineral dissolution and subsurface volume contraction affect overlying soils. In this study, we examine the consequences of mass loss or volume contraction at shallow depths using a discrete element method. The goal of the study is to identify particle-scale and global effects as a function of the relative depth of a dissolving inclusion, initial soil density, and granular interlocking. There are successive arch formation and collapse events, and a porosity front propagates upwards as grains slide down to refill the space. Grains around and within the refilled cavity are loosely packed and have small contact forces that are sufficient to avert the buckling of granular arches that form around the dissolving zone. Denser packings and interlocking combine to exacerbate rotational frustration and lead to more pronounced force chains along granular arches, looser fill, and reduced surface settlement. In fact, surface settlement vanishes, and the sediment hides the localized dissolution when deep inclusions z/D ≥ 5 dissolve within dense sediments. While scaling relations limit the extrapolation of these numerical results to tunneling and mining applications, macroscale trends observed in the field resemble results gathered in this study.

Effect of grain dissolution on sloping ground

“…The time scale for chemical processes is typically quite long and the "inert assumption of soils" applies to many engineering applications. However, dissolution and precipitation can also take place within relatively short time scales in advective regimes such as infiltration-induced carbonate dissolution and when systems are taken far from equilibrium in young systems such as dam foundations, mine tailings, fly ash, volcanic ash, and CO 2 injection [1][2][3][4][5][6][7][8][9][10][11][12][13] .Waste is particularly vulnerable to dissolution and degradation because its components are suddenly exposed to new environmental conditions outside equilibrium. Heavy metals and acid drainage from mine tailings and fly ash ponds are early signs of ongoing dissolution processes 14,15 .…”

“…The time scale for chemical processes is typically quite long and the "inert assumption of soils" applies to many engineering applications. However, dissolution and precipitation can also take place within relatively short time scales in advective regimes such as infiltration-induced carbonate dissolution and when systems are taken far from equilibrium in young systems such as dam foundations, mine tailings, fly ash, volcanic ash, and CO 2 injection [1][2][3][4][5][6][7][8][9][10][11][12][13] .…”