In most design codes, soils are classified as either sand or clay, and appropriate design equations are used to represent their behaviour. For example, the behaviour of sandy soils is expressed in terms of the soil’s relative density, whereas consistency limits are often used for clays. However, sand-clay mixtures, which are typically referred to as intermediate soils, cannot be easily categorized as either sand or clay and therefore a unified interpretation of how the soil will behave at the transition point, i.e., from sandy behaviour when fines are few to clay behaviour for high fines content, is necessary. In this paper, the cyclic shear behaviour of sand-silt mixtures was investigated by considering variations in fines content and compaction energy, while paying attention to the void ratio expressed in terms of sand structure. Then, by using the concept of equivalent granular void ratio, it was noted that the contribution of silt on the cyclic shear strength of the soil was about 43% of that of sand.