Fabric evolution during hydromechanical loading of a compacted silt

Abstract

SUMMARYA study was undertaken on a compacted silt to determine fabric modifications induced by suction and/or stress variations. The link between fabric and hydromechanical behaviour was also investigated. A suctioncontrolled oedometer, using air overpressure, was developed for this purpose and mercury intrusion porosimetry was employed to determine sample fabric. The initial samples fabric was made of macro and micropores. It was shown that suction increase produced a strong decrease in the macroporosity associated with an increase in microporosity. However, some macropores were not significantly affected by the suction increase; this phenomenon might be related to the initial fabric of the samples. Second, it appears that loading under saturated conditions also produces strong fabric modification: the higher the applied stress, the lower the macroporosity. Soil fabric depends on the maximum stress experienced by the soil. Finally, some tests have shown the influence of suction, as well as the role of the degree of saturation, on the deformation process and the mechanical behaviour. The test results show that in the case of unsaturated mechanical loading, all macropores are not destroyed by the mechanical loading.

The role of compaction energy on the small strain properties of a compacted silty sand subjected to drying–wetting cycles

“…8). In addition, microstructural studies have reported that the soil fabric during drying is also evolving into a more constricted porosity centred at the microporosity range, although it recovers some of the macroporosity when it is subsequently wetted (Cuisinier & Laloui, 2004;Monroy et al, 2010). These results are also consistent with the small strain shear modulus studies on decomposed tuff and Bonny silt conducted by Ng & Xu (2012) and Khosravi & McCartney (2012).…”

“…Lourenco et al, 2012) and the variation in soil structure during drying-wetting cycles (e.g. Cuisinier & Laloui, 2004). In this context, the ink-bottle effect refers to the soil-water exchange occurring within the soil pores to mimic the existence of large pores connected through smaller pores.…”

Suction Induced Effects on the Fabric of a Structured Soil

“…Natural soils show different structures, characterised by structural units, such as aggregates, porous block, fissures, earthworm holes and root channels (especially in the top layers of agricultural soils). It is widely accepted in the literature (Griffiths and Joshi, 1990;Gens et al, 1995;Al-Mukhtar et al, 1996;Delage et al, 1996;Cuisinier and Laloui, 2004) that these soils, especially the compacted ones, have two levels of structure: macro and micro. The soil microstructure can be defined as the elementary particle associations within the soil aggregates (Al-Mukhtar et al, 1996), whereas the arrangement of these soil aggregates and the relation among the structural units at the aggregate level is referred to as the macrostructure.…”

“…Consequently, the pores of a soil consist of two main classes, micropores and macropores, corresponding to the two levels of soil structure. These two different levels play important roles in the hydro-mechanical behaviour and deformation process of soils (Cuisinier and Laloui, 2004). For instance, although micropores are usually neglected, they have a strong influence on water retention characteristics.…”

Influence of microfabric evolution on the retention behaviour of compacted clayey soils

“…This fabric is not unique and the size of the aggregates appears to be sensitive to the compaction water content (Thom et al 2007), the chemical composition of the interstitial fluid (Musso et al 2013) and the particular hydromechanical path followed (Delage, 2010). Furthermore, the structure is not fixed but evolves along stress-paths (see for instance Romero et al 1999, Cuisinier & Laloui 2004, Della Vecchia 2009, Monroy et al 2010, Wang et al 2012.…”