## 1 Introduction  
Soils are the most required resource for construction purposes either for buildings or for roads. Some soils are naturally suitable for construction purposes, others are not. The soils that are not suitable for construction are referred to as problematic soils, as described in [PERSON] [1] and [PERSON] and [PERSON] [2]. Examples of problematic soils include expansive soils, which are commonly observed due to their worldwide occurrence except in the Artic region [1; 3], loess or sandy soils, etc. These soils usually exhibit low shear strength, high compressibility, high susceptibility to volume changes, and sensitivity to moisture content [2; 4]. Therefore, there is a need to improve the natural properties of such soils for construction purposes in a process called soil stabilisation. This can be achieved through physical or chemical soil stabilisation methods. Physical soil stabilisation methods include compaction, consolidation, mixing soils of different grain size to obtain a well-graded soil for construction purposes, and finally removal of existing soil and replacing it with a natural soil deposit suitable for construction [1; 5; 6]. Soil chemical stabilisation methods have been used in recent decades [7; 8; 9; 10; 11] to improve slopes, foundation structures, increase slope stability, prevent liquefaction, and stabilise contaminated soils, among others [9; 12; 13]. The major disadvantage of using a chemical soil stabilisation method is the low or no tensile or flexural strength of the stabilised soil when required to accommodate horizontal vibrations or horizontal displacements, from earthquakes, heavy machinery, traffic, wind, ocean waves, and explosives [4; 9]. Therefore, an alternative method has been developed, in which short fibres are introduced into soil-binder mixtures to improve flexural and tensile behavior, independent of other mechanical properties such as the elastic modulus (E\({}_{u.50}\)) and compressive strength of the soil [9; 14; 15]. The effective use of short fibres in soil-binder-water mixtures has been extensively studied by different authors, especially based on unconfined compressive strength (UCS) and indirect tensile strength (ITS) tests [4; 8; 9; 14; 16; 17]. The findings demonstrate how inclusion of short fibres changes with the type of soil, the type and content of fibres, the amount of binder, and the test mechanism used [4; 9; 14; 18]. [PERSON] and [PERSON] [19] found that the UCS, ITS and E\({}_{u.50}\) values of soil-cement-fibre mixtures normally either remained the same or were higher than those of soil-cement mixtures. [PERSON] et al. [20] indicated that the addition of fibres increases the residual strength and converts the brittle behavior of the soft clay treated with cement into a ductile material. [PERSON] and [PERSON] [21], [PERSON] et al. [9], [PERSON] [22], [PERSON] et al. [23], and [PERSON] [24] pointed out, however, that compressive strength is related to the value of E\({}_{u.50}\), where E\({}_{u.50}\) increases with the progress of hydration, curing time, clay content, cement dosage, and fibre content. [PERSON] and [PERSON] [21] show this through experimental equations of compressive strength and elastic modulus, E\({}_{u.50}\). Thanks to this knowledge and understanding, it becomes clear that the compressive strength and E\({}_{u.50}\) are intimately linked. Moreover, an increase in E\({}_{u.50}\) is directly proportional to the compressive strength. Several factors are considered when conducting experiments to evaluate the mechanical properties of soil-cement-fibre mixtures. Cost, time, and most important, the ability to reproduce actual field conditions [4], are some of the factors. Thus, the use of prediction tools will go a long way to solve experimental problems such as cost and time. Moreover, this is especially helpful in predicting the mechanical properties of soil-cement mixtures reinforced with fibres during the design phase.