Effects of the maximum soil aggregates size and cyclic wetting–drying on the stiffness of a lime-treated clayey soil

Abstract

Lime treatment is a well-known technique to improve the mechanical response of clayey subgrades of road pavements or clayey soils used for embankment. Several studies show that lime treatment significantly modifies the physical and hydromechanical properties of compacted soils. Nevertheless, studies on the scale effect under climatic changes are scarce. Actually, wetting–drying cycles might significantly modify the microstructure of treated soils, giving rise to changes in hydromechanical properties. This modification could be dependent on the size of soil aggregates before lime treatment. In the present work, this scale effect was studied by investigating the stiffness of a compacted lime-treated clayey soil using bender elements. The studied soil was first air-dried and ground into a target maximum soil aggregates size (Dmax). For each aggregate size, the soil was humidified to reach the target water contents wi, then mixed with 3% of lime powder (mass of lime divided by mass of dried soil) prior to the static compaction at a dry density of 1·60 Mg/m3. Two initial water contents (wi = 14 and 18%) and four maximum soil aggregates sizes (Dmax = 0·4, 1·0, 2·0 and 5·0 mm) were considered. After the compaction, the soil specimen (50 mm in diameter and 50 mm high) was covered by plastic film in order to prevent soil moisture changes. The soil stiffness was then monitored at variable time intervals until reaching stabilisation. Afterwards, the soil specimen was subjected to full saturation followed by air-drying to come back to its initial water content. The results show that: (a) the soil stiffness after lime-treatment is significantly dependent on the aggregate size: the finer the aggregates the higher the soil stiffness; (b) the effect of initial water content on the stiffness is negligible; and (c) the wetting–drying cycles seem to slightly increase the soil stiffness in the case of lime-treated specimens and decrease the soil stiffness in the case of untreated specimens. Furthermore, when an intensive drying was applied reducing the soil water content lower than the initial level, the soil stiffness decreased drastically after the subsequent wetting.

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

“…The three different compaction energy levels adopted for the 50 mm diameter mould were adjusted to match the target dry unit weights obtained for the traditional Proctor mould for energy levels of 357 kJ=m 3 , 596 kJ=m 3 and 832 kJ=m 3 following the procedure reported by Sridharan & Sivapullaiah (2005). Similar procedures have been followed in numerous past studies too, for example, Seed & Chan (1959), Reddy & Jagadish (1993) and Tang et al (2011), among others. These specimen dimensions were selected so the diameter and height of the specimen would minimise the near-field effects (Leong et al, 2005).…”

Effects of aggregate size on the compressibility and air permeability of lime-treated fine-grained soil

“…This can be closely related to the different aggregate sizes considered in the field and in the laboratory. Indeed, in addition to the climate conditions, the aggregate size can play an essential role in the lime treatment (Tang et al, 2011a).…”

“…To the authors' knowledge, there are a few studies on the aggregate size effects. Tang et al (2011a) and Dong (2013) studied the aggregate size effect on the stiffness of lime-treated soils during curing and concluded that the treated soils with larger aggregates exhibit a lower small-strain shear modulus and lower resistance to wetting/drying cycles. Wang et al (2015) reported a relatively higher water retention capacity for the treated soil with smaller aggregates.…”

Editorial: partial saturation in compacted soils

“…The present issue has, instead, a more applicative focus with contributions covering barrier systems for underground disposal of nuclear waste, earth dams and embankments, as well as a study of lime-treated compacted clays. The first three contributions in the present issue are dedicated to the sub-theme 'application to engineering problems and case studies' (Alonso et al, 2011a;Gens et al, 2011;Thorel et al, 2011) while the last two contributions are devoted to the sub-theme 'material characterisation' (Taibi et al, 2011;Tang et al, 2011).…”

“…In the fourth article, Tang et al (2011) explore the reasons why the small-strain stiffness of lime-treated compacted soils tends to be lower for samples retrieved from the field compared to similar samples prepared in the laboratory. The authors identify two possible causes for such behaviour, namely the degradation of inter-granular cementation due to wetting-drying cycles induced by the in situ climatic conditions and the coarser grain size of field samples in comparison with laboratory-prepared samples.…”