Thesis Details

Thesis Title: The effects of fiber cross-section and needlepunch density on strength and water permeability of needlepunched nonwoven geotextiles
Thesis Author: Michael Hill
Abstract: Nonwoven geotextiles are permeable structures made of fibers bound by mechanical or chemical means. These textiles are used by civil engineers in conjunction with soils or rocks in numerous applications. Today, the application of geotextiles for reinforcement, separation, filtration, and drainage in civil engineering applications is a sophisticated process. This rapidly developing industry has promoted vast new areas of research. The focus of this thesis was to determine the effects of fiber cross-section and needlepunch density on the physical properties of needlepunched nonwoven geotextiles. Three fiber cross-sections were each needlepunched at four levels of needlepunch density. Round, delta, and bilobal were the three cross-sections used for the study. All other fiber variables were held constant, with exception of fiber tenacity. The round fiber had the highest fiber tenacity, followed by the delta and bilobal fibers, respectively. The three fibers were each needlepunched at 600, 800, 1000, and 1200 punches/in2. All other processing variables were held constant at levels determined by industry practice. Bilobal fibers produced fabric with the highest strength-to-weight ratio (fabric tensile strength in lbs, divided by fabric weight in oz/yd2). Delta and round fibers produced fabrics with approximately equal strength-to-weight. The bilobal-fiber fabric outperformed the round and delta-fiber fabrics because of increased fiber surface area, which led to increased fiber-to-fiber cohesion. This fabric result was especially significant, considering the low fiber tenacity of the bilobal fiber as compared to the round and delta fibers. It was concluded that the fiber tensile strength test results may not be an accurate predictor of fabric tensile strength in the case of the bilobal fiber. Bilobal fibers did produce fabric with the lowest tear strength, because of a decrease in fiber mobility when the fibers were needlepunched. Bilobal fibers produced fabric with lower water permeability than fabrics constructed of round or delta fibers. The results support the theory that fabrics with the highest bulk density demonstrate the lowest water permeability. The bilobal fiber was easier to compress than round or delta fibers, because of its low flexural rigidity. Fabric strength-to-weight ratio increased as heedlepunch density increased, due to more fiber entanglements at the higher punch densities. The point was not reached in this research where increased needlepunch density led to fiber breakage. Needlepunch density had little effect on fabric tear strength. Increases in needlepunch density generally led to decreases in fabric water permeability. Increased needlepunch density resulted in increased fabric compaction, lowering water permeability.