Physical and chemical reinforcements are commonly used to improve sand properties for engineering requirements. Many researchers have concluded that composite reinforcement can greatly improve sand property strength. In this paper, polyurethane organic polymer (PU) and polypropylene fiber (PF) were used to reinforce sand. It is found that composite reinforcement has great effects on tensile strength. A series of direct tensile tests were conducted to demonstrate this reinforcement and to investigate the effects of PF content, PU content, dry density, and curing time. Additionally, the reinforcement mechanism was analyzed by scanning electron microscope images. The tensile strength increases with curing time until it reaches a plateau. The composite reinforcement improves the tensile strength exponentially with the increase of PF and PU contents. For the effect due to dry density, the tensile strength first increased and then decreased with the peak at approximately 1.55 g/cm³. Through the interaction force among fibers and sand particles and the bonding force of polymer among sand particles, tensile strength of reinforced sand is greatly improved.
Keywords: composite reinforcement; dry density; geosynthetics; interaction mechanism; polymers; tensile strength.