Investigation of the Water-Retention Characteristics and Mechanical Behavior of Fibre-Reinforced Unsaturated Sand  
[PERSON]  
1 State Key Laboratory of Intelligent Geotechnics and Tunnelling, College of Civil and Transportation Engineering, Shenzhen University; Shenzhen 518060, China; [EMAIL_ADDRESS]  
[EMAIL_ADDRESS]  
[PERSON]  
1 State Key Laboratory of Intelligent Geotechnics and Tunnelling, College of Civil and Transportation Engineering, Shenzhen University; Shenzhen 518060, China; [EMAIL_ADDRESS]  
[EMAIL_ADDRESS]  
[PERSON]  
1 State Key Laboratory of Intelligent Geotechnics and Tunnelling, College of Civil and Transportation Engineering, Shenzhen University; Shenzhen 518060, China; [EMAIL_ADDRESS]  
[PERSON]  
1 State Key Laboratory of Intelligent Geotechnics and Tunnelling, College of Civil and Transportation Engineering, Shenzhen University; Shenzhen 518060, China; [EMAIL_ADDRESS]  
[PERSON]  
1 State Key Laboratory of Intelligent Geotechnics and Tunnelling, College of Civil and Transportation Engineering, Shenzhen University; Shenzhen 518060, China; [EMAIL_ADDRESS]  
[PERSON]  
1 State Key Laboratory of Intelligent Geotechnics and Tunnelling, College of Civil and Transportation Engineering, Shenzhen University; Shenzhen 518060, China; [EMAIL_ADDRESS]  
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fibres was observed to improve the shear strength and cohesion of soil significantly [21]. The use of 6 mm-long fibres evenly distributed in soil was found sufficient to form a soil network to bear external loads. Based on a modified hyperbolic model, a nonlinear regression model was established to predict the effective shear-stress ratio. However, most of the studies have focused on saturated or dry soil; soils are usually in an unsaturated state in actual engineering. In the study of [PERSON] and [PERSON] [19], soil strength was proposed to be a function of moisture and fibre contents. Moreover, the addition of fibre to sand and clay was suggested to increase the peak-friction angle and improve cohesion. [PERSON] et al. [25] reported that adding fibres to soil could increase the peak-friction angle of a specimen; however, this observation differs from that of other research [26]. Despite extensive research on the mechanical properties of fibre-reinforced soils, including fibre type [20; 27; 28], content [21; 29; 30; 31], and distribution direction [32; 33; 34; 35], studies on fibre-reinforced soil considering moisture content are few ([PERSON] and [PERSON] [19] and [PERSON] et al. [26]). As mentioned, most studies have focused on dry or saturated soils; however, the cases are different from the actual conditions. Moreover, the relationship between fibre reinforcement and moisture content is not fully understood. Therefore, investigating the effects of fibre length, fibre content, and moisture content on the shear resistance of soil is necessary. On another hand, previous research has also shown that the addition of fibres can affect the water-retention characteristics of soil. For example, the effect of polypropylene (PP) fibre inclusions on the soil-water characteristic curve (SWCC) of expansive soils was investigated [36]. The fibres were found to enhance the bond among soil particles. Moreover, an increase in air entry was observed during soil desaturation. This agrees with the findings reported in the study of [PERSON] [37] that the increasing amounts of fibre in fine-grained soils lead to higher desaturation degrees. The addition of fibres was shown to increase the water-retention capacity of soil because of the additional contact zone created between the soil and fibres [38]. The residual moisture content and water-retention capacity of fibre-reinforced soil were reported to increase with the fibre content [11].