Experimental Study on Engineering Properties of Expansive Soil Improved by Coal Gangue with Different Particle Sizes

Abstract

In order to investigate the effects of coal gangue particle size and content on the properties of expansive soil, a series of laboratory tests including compaction test, swelling test, direct shear test, and unconfined compressive strength test were carried out. Three particle size groups of coal gangue (0–2 mm, 2–5 mm, and 5–10 mm) and six content levels (0%, 5%, 10%, 15%, 20%, and 25%) were selected. The results show that, for the same particle size, the maximum dry density of the mixture increases with increasing coal gangue content, while the optimum moisture content decreases. All particle sizes of coal gangue can effectively inhibit the swelling behavior of expansive soil, and the inhibition effect becomes more significant with increasing content, particularly at 15%. Under the same content, larger particle sizes exhibit better swelling suppression effects. For shear strength, the internal friction angle and cohesion fluctuate significantly when small (<2 mm) or large (>5 mm) particles are added, while the optimal improvement is achieved at a particle size of 2–5 mm and a content of 15%–20%. The unconfined compressive strength increases first and then decreases with increasing content, reaching a peak at 15%. Meanwhile, under the same content, the strength decreases with increasing particle size, and the optimal combination for compressive strength is 0–2 mm particle size with 15% content.