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| Authors | Test apparatus | Type of reinforced soil tested | Remarks |
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| Lawton et al. 1993 [101] | California bearing ratio (CBR), triaxial, and permeability tests | A nonplastic, residual silty micaceous sand and Ottawa sand mixed with multioriented geosynthetic | The usage of multioriented geosynthetics rises the stiffness of the soil. Furthermore, a 584% increase was seen in the stress-strain modulus and a 106% increase was seen in deviator stress at failure. Multioriented and fiber geosynthetics reduce the penetration resistance at small values whereas fiber exhibited better resistance at larger penetration values. Finally, fiber reinforcement was seen to provide a better effect on the soil compared to multioriented at the same amount. The optimum fiber content was 3% by volume |
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| Rao et al. 2005 [100] | Triaxial compression test | Yamuna sand reinforced with coir fiber and coir geotextiles | The inclusion of coir fiber rises the shear strength and increases the deviator stress at failure. Randomly distributed coir fiber displayed far superior strength in comparison to layered coir fiber. The usage of reinforcement showed influence in the reduction of volumetric expansion. The reinforced and unreinforced sand exhibited the same increasing effect on the initial tangent and secant modulus with the increase in confining pressure. The optimum coir fiber content was 1% by weight |
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| Damarashetty et al. 2006 [102] | Triaxial compression test | Sand mixed with coir fiber | The integration of coir fiber as a reinforcement element in the sand was seen to increase the effective friction angle up to critical confining pressure of 49 kPa. Past the critical pressure, the effective cohesion. Coir fiber can be utilized in the ground improvement of soil. The optimum fiber content was 1% |
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| Sivakumar Babu and Vasudevan 2008 [62] | Triaxial shear test | Clay mixed with coir fiber | The presence of coir fiber (1%–2%) in the soil leads to stiffness and strength increase. Additionally, the usage of fiber enhances the stress-strain relationship. The maximum increase in stress can be achieved with the fiber length between 15 and 25 mm. The use of fiber in the soil causes a rise in the stiffness of the mixture in terms of minimizing the immediate settlement. The optimum fiber content found to be 2%–2.5% (by weight of soil) |
| Kafodya and Okonta 2019 [103] | Undrained cyclic and postcyclic shear tests | The soil used is a mixture of clay-silt, sand, and gravel with sisal fiber | The increment of shear modulus was related to the fiber content up to 0.5% where beyond that the shear modulus starts decreasing due to the drop in stiffness of the soil mixture caused by the presence of voids. As the confining pressure increased, the shear modulus increased. The usage of fiber and the increment in confining pressure improved the damping ratio due to the improvement in the resistance of soil mixture to deformation. The liquefaction resistance was seen to be high in unreinforced and reinforced soils due to the presence of fine particles while fiber limited the generation of pore water pressure. The optimum fiber content was 0.5% |
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| Ertuğrul and Canoğulları 2022 [104] | Regression analysis using the results of the other related studies | Different soils mixed with different natural and synthetic fibers | Regression analysis was performed using previous studies in the field to examine the effect of adding natural or synthetic fibers on the liquefaction of soil by means of relative density and fiber content. The results of the proposed formula obtained using regression analysis matched the results of previous studies with a coefficient of determination of 0.90 in which the increase in fiber percentage increased the number of cycles to reach liquefaction. The optimum fiber content was 1% which represented the best improvement against liquefaction |
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