Abstract
The swelling properties of expansive soils can be reduced by the addition of modifiers. Nevertheless, the performance deterioration after modification occurs when weathering for a long term. Therefore, in this study, the effect of drying-wetting cycles on swelling behaviour and compressibility of modified expansive soils with the iron tailing sand and calcium carbide slag has been investigated. The swelling potential initially increases and subsequently decreases with the increasing number of cycles, reaches the peak at the seventh cycle, and tends to equilibrium after the tenth cycle. These results show that drying-wetting cycles will destroy the soil structure. The compressibility of modified expansive soils increases with the drying-wetting cycles, where an empirical formula between compressibility and the cycle number was established. Microstructural analysis is performed using mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The results of microstructural analysis show a tendency of degradation process.
Highlights
Expansive soils are highly plastic soils and are mainly composed of hydrophilic clay minerals. e behaviour of expansive soils changes with the water mass, i.e., expanding when absorbing water and shrinking when discharging water [1, 2]. e longterm evolution in climate and hydrological conditions will cause progressive alteration in deformation and strength, leading to the degradation of geo-based structures, including the highway, railway, slope, and foundation, and causing a significant financial loss annually in the world [3,4,5].Many improvement technologies have been proposed and applied in engineering practices, such as replacement, compaction, moisture control, chemical modification, and thermodynamics methods
Iron tailing sand composes of the fine and stable fraction, which could be used to optimize the particle size distribution [17, 18], the swelling pressure [19], and the shear strength [20] of expansive soil. erefore, it is applicable to recycle these wastes as expansive soil modifiers
The effects of drying-wetting cycles on the free swelling ratio, the swelling pressure, and the compressibility of expansive soils improved by the iron tailing sand and calcium carbide slag were explored
Summary
Expansive soils are highly plastic soils and are mainly composed of hydrophilic clay minerals (i.e., montmorillonite group minerals). e behaviour of expansive soils changes with the water mass, i.e., expanding when absorbing water and shrinking when discharging water [1, 2]. e longterm evolution in climate and hydrological conditions will cause progressive alteration in deformation and strength, leading to the degradation of geo-based structures, including the highway, railway, slope, and foundation, and causing a significant financial loss annually in the world [3,4,5]. Many improvement technologies have been proposed and applied in engineering practices, such as replacement, compaction, moisture control, chemical modification, and thermodynamics methods Chemical additives such as cement, lime, and fly ash have been confirmed to effectively change the plasticity and swelling characteristics of the expansive soils [6,7,8,9]. Despite that cement and lime have been extensively used as they are cost effective, many industrial wastes, such as recycled fiber, glass, iron tailing sand, and carbide slag, have been regarded as the substitution of traditional modifiers for environmental protection and economic benefits [10,11,12,13,14]. The effects of drying-wetting cycles on the free swelling ratio, the swelling pressure, and the compressibility of expansive soils improved by the iron tailing sand and calcium carbide slag were explored. Microstructure was investigated by the mercury intrusion porosimeter (MIP) and scanning electron microscope (SEM) tests as well to clarify the internal mechanism
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