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.

By conducting undrained cyclic triaxial tests on fibre-reinforced very loose and loose saturated sand, we investigated the build-up of excess pore pressure and the flow liquefaction responses. The test results show that unreinforced very loose and loose saturated sand has a high potential for liquefaction, with flow liquefaction occurring in all unreinforced samples under undrained cyclic loading. The presence of fibre reinforcement has a positive impact on the resistance to flow liquefaction of sand. Fibres provide both a densifying effect and a confining effect to the sand skeleton. However, the confining effect of fibres depends on the loading path imposed on the samples and the deformation mode of the samples. The presence of fibres alters the evolution law of the residual excess pore pressure in saturated sand. When fibres impose a strong confining effect on the sand skeleton, the evolution of residual excess pore pressure along with the normalized loading cycles follows a curve with an 'inverted L' shape, being significantly different from an 'S' shape curve which is followed by the unreinforced sand. Under the two-way symmetrical and one-way cyclic loading, the significant fibre stress contribution is mobilized, leading to the effective stress of the sand skeleton being much greater than 0 after the 100% build-up of excess pore pressure. As a result, the strength loss of the reinforced sample remains below 11% and thus the fibres prevent liquefaction from developing.