Abstract
Abstract A collapsible soil is composed essentially of a packing of mineral particles and a set of interparticle bonds holding the system together. Failure requires the bond system to fail and the soil structure to collapse. A natural hazard is presented. The soil structure may collapse inwards (consolidate), as in loess failure, or it may collapse outwards (disperse, disintegrate), as in the failure of quick-clays, some collapsing sands, some silty estuarine deposits, and in wind erosion of silty soils by saltating sand grains. Generalising about bonding systems allows two types of interparticle bond to be recognized: long range bonds and short range bonds. Long range bonds are found in clay mineral systems and allow the occurrence of plasticity. They are represented by c in the standard Coulomb equation. Short range bonds are found in inactive particle systems. These are soil systems where the constituent particles do not have a significant electrical charge. A slight deformation of a short-range bonded system causes much loss of strength. It is short range bonds which tend to dominate in collapsing soil systems, although in the complex case of loess the bond failure is initially mediated by long range bonds at the interparticle contact regions. A collapse failure involves a large scale remaking of the soil structure, and thus total failure of the bonding system. Generalising again- it can be claimed that five types of particle make up engineering soils: A active clay mineral particles (the smectites), B inactive clay mineral particles (e.g. kaolinite, illite), C very small inactive primary mineral particles (close to the comminution limit in size- mostly in the quick-clays), D silt (usually quartz silt), and E sand (usually quartz sand). The nature of type D particles contributes to the collapse of loess soils, the most widespread of the collapsing soil phenomena. The nature of type C particles controls the behaviour of quick-clays. C and D systems are essentially dominated by short-range bonds.
Highlights
Collapsible soils can be divided into two types: a) those in which an open structure collapses into a more compact structure(perhaps these are the classic, default collapsible soils), and b) those in which a soil structure disintegrates into a totally dispersed system
A slight deformation of a short-range bonded system causes much loss of strength. It is short range bonds which tend to dominate in collapsing soil systems, in the complex case of loess the bond failure is initially mediated by long range bonds at the interparticle contact regions
We are concerned with the interparticle bonds which have to be broken for the system to collapse; it would be useful to clarify the nature of the various types of collapsing soil and to define some of the collapse actions and consequences
Summary
Collapsible soils can be divided into two types: a) those in which an open structure collapses into a more compact structure(perhaps these are the classic, default collapsible soils), and b) those in which a soil structure disintegrates into a totally dispersed system. There have not been many studies of interparticle bonding in engineering soils, perhaps the most perceptive was that by Osipov [3]. This topic falls within the field of ‘engineering soil science’ which has always been more thoroughly pursued in Russia than in other countries, so most of the literature on engineering soil bonding and collapse problems in engineering soils is in Russian (see, in particular Sergeev et al [4], Trofimov [5], Kriger [6], Kriger et al [7] and for a review of early studies Drashevska [8] – which is highly recommended)
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