A common physical technique assessed for improving expansive clays is by the addition of natural fibres to the soil. A good understanding of the impact of stabilisation using fibres on the clay soil's constituents, microfabric, and pore structure is, however, required. Mixtures of clay and fibre, regardless of type or extent, can never change the natural composition of the clay. Even the smallest part must still consist of spaces with clay with the original physical properties and mineralogy. This suggests that, although the mixture may show beneficial physical changes over the initial clay soil, its spatial attributes in terms of mineralogical characteristics, remain unchanged. This paper discusses some of the fundamentals that are not always adequately considered or addressed in expansive clay research, aiming to improve the focus of current and future research investigations. These include the process, mechanics, and implications of chemical and physical soil treatment as well as the concept of moisture equilibration.

Sodium hydroxide (NaOH)-sodium silicate-GGBS (ground granulated blast furnace slag) effectively stabilises sulfate-bearing soils by controlling swelling and enhancing strength. However, its dynamic behaviour under cyclic loading remains poorly understood. This study employed GGBS activated by sodium silicate and sodium hydroxide to stabilise sulfate-bearing soils. The dynamic mechanical properties, mineralogy, and microstructure were investigated. The results showed that the permanent strain (epsilon(p)) of sodium hydroxide-sodium silicate-GGBS-stabilised soil, with a ratio of sodium silicate to GGBS ranging from 1:9 to 3:7 after soaking (0.74%-1.3%), was lower than that of soil stabilised with cement after soaking (2.06%). The resilient modulus (E-d) and energy dissipation (W) of sodium hydroxide-sodium silicate-GGBS-stabilised soil did not change as the ratio of sodium silicate to GGBS increased. Compared to cement (E-d = 2.58 MPa, W = 19.96 kJ/m(3)), sulfate-bearing soil stabilised with sodium hydroxide-sodium silicate-GGBS exhibited better E-d (4.84 MPa) and lower W (15.93 kJ/m(3)) at a ratio of sodium silicate to GGBS of 2:8. Ettringite was absent in sodium hydroxide-sodium silicate-GGBS-stabilised soils but dominated pore spaces in cement-stabilised soil after soaking. Microscopic defects caused by soil swelling were observed through microscopic analysis, which had a significant negative impact on the dynamic mechanical properties of sulfate-bearing soils. This affected the application of sulfate-bearing soil in geotechnical engineering.

Shredded rubber from waste tyres has progressively been adopted in civil engineering due to its mechanical properties, transforming it from a troublesome waste into a valuable and low-cost resource within an eco-sustainable and circular economy. Granular soils mixed with shredded rubber can be used for lightweight backfills, liquefaction mitigation, and geotechnical dynamic isolation. Most studies have focused on sand-rubber mixtures. In contrast, few studies have been conducted on gravel-rubber mixtures (GRMs), primarily involving poorly-graded gravel. Poorly-graded gravel necessitates selecting grains of specific sizes; therefore, from a practical standpoint, it is of significant interest to examine the behaviour of well-graded gravel and shredded rubber mixtures (wgGRMs). This paper deals with wgGRMs. The results of drained triaxial compression tests on wgGRMs are analysed and compared with those on GRMs. Stress-strain paths toward the critical state and energy absorption properties are evaluated. The tested wgGRMs exhibit good shear strength and remarkable energy absorption properties; thus, they can be effectively utilised in several geotechnical applications.