A study on the mechanical behaviour of mixed fiber-reinforced soil

Mixed fiber reinforced technique has been widely used in reinforcing the concrete due to its excellent performance in enhancing the strength, durability and stiffness. The improvement of fiber-reinforced soil (FRS) on the mechanical behaviour (e.g., stiffness and ductility) is limited due to the properties of single fibers. However, much studies focus on the single fiber based reinforced soil, two fibers or more mixing with soil do not be covered. Mixed fiber-reinforced soil (MFRS) is defined as the improvement of FRS, in which two different types of fibers are mixed into the soil to improve the shear strength and stiffness simultaneously. The tests were conducted using clay soil and Yongjiang sand, which were collected from the practical construction site of metro and Yongjiang River, respectively. The test results show that under the same test conditions (e.g., void ratio, confining pressure and fiber content), the MFRS always show higher deviator stress than the FRS. As carbon fibers and polypropylene fibers give higher stiffness and tensile strength respectively. Besides, the friction angle and cohesion of MFRS are also affected by fiber content. It is concluded that half of the carbon fiber content of MFRS has the same performance in the stress-strain relationship as the FRS with 100% carbon fiber content. However, the effectiveness of the reinforcement to clay soil is insignificant. As the reinforcements is relatively dependent on the characteristics of clay soil (e.g., mean diameter, coefficient uniformity). For the use of MFRS, it could decrease the cost of purchasing special fiber such as pure carbon fiber and aramid fiber, which are expensive, and it could be used in the long-terms constructions, which are required to last at least 100 years.