The open metastable structure of a collapsible sand: fabric and bonding

Abstract

This paper deals with the compositional and textural characteristics determining open metastable structures in the pleistocenic sand outcropping in the Agrigento district (Sicily). The aim of the study was to individuate the bonding types occurring between grains that could generate matric suction phenomena. The composition and microfabric were characterised by means of granulometry, porosimetry, permeability, optical and ESEM-EDS microscopy, thermogravimetry and XR diffractometry, electric conductivity, and ionic chromatography. The data thus acquired show that the skeleton of the sand is constituted mostly by bioclasts and microfossils, calcite and quartz monocrystalline grains. Moreover, assemblages of silt and clay minerals are interposed among them. Cementation is generally absent even at the sites of contact between grains. Porosity is due mainly to interparticle voids. The spatial arrangement of sand, silt and limey grains, the pore geometry, volume and size distribution and network connectivity allow both capillary condensation and effective capillary transport of water. It appears that bonding is due mainly to capillary forces related to the texture and to the type of pores rather than being ruled by composition.

Mineral composition of terrigenous components in loess and clay deposits of Western Mongolia

“…Широко развиты связные пески (ps*), которые в виде делювиально-эоловых покровов залегают на пологих склонах и поверхности надпойменных террас Орхона (d-vQ 3-4 ) или представляют аллювиальный комплекс (aQ 4 ). Пески со следами связности характеризуются присутствием агрегатов, в которых заключен резерв глинистых фракций; в зарубежных публикациях агрегированные просадочные пески называются глинистыми [24].…”

Determination of Water Retention Properties of Silty Sands by Means of Combined Commercial Techniques

“…The first one refers to the stability of regional dykes in The Netherlands, which are experiencing droughts due to substantial increase in summer temperatures in the recent years [1]. The second case refers to natural cliffs made of carbonate sand at Agrigento in Italy, where local collapses have been observed following heavy rainfalls [2][3][4][5]. Both cases involve large areas, for which management decisions have to be taken based on a relatively small amount of data, as advanced lengthy laboratory investigation cannot be afforded.…”

Effect of Matric Suction on Deformation of Gypseous Sand Using Modified Oedometer

“…Gypseous soils experience numerous changes in their physical and mechanical characteristics due to their exposure to continuous mass loss [18]. The soils' bearing capacity is decreased by about 50% due to the soaking process [19]. The shear strength of the soil can be improved by advancing the soaking time (long term) before shearing [20,21].…”

“…The unsaturated state always presents in collapsible soils where large collapse occurs with a decrease in the matric suction (𝑢𝑎−𝑢𝑤) [18]. During wetting in the sand, a sudden reduction in volume occurs, as observed by means of granulometry, porosimetry, permeability, optical and ESEM-EDS microscopy, thermogravimetry and XR diffractometry, electric conductivity, and ionic chromatography [19]. Unsaturated soil changes its volume when the magnitude of the "𝑢𝑎−𝑢𝑤" or the net normal stress changes, and this leads to the occurrence of the phenomenon of collapse [23,24].…”