Assessment of creep on long-term performance and calibration factor of geosynthetics in geoenviormental applications

Abstract

Geosynthetics became one of the outstanding innovations with ever-growing significance for geotechnical and geo-environmental engineering industry. Earthwork construction over soft polluted sludge lagoons and tailing impoundments is mandatory to cap various waste materials. Low shear strength and high compressibility of such soil deposits expose short and long-term geotechnical challenges. Geosynthetics provide strengthening and allow accessibility over these deposits, which save money and reduce carbon footprint. Like all polymeric products, geosynthetics are susceptible to creep. However, creep data is not published by manufactures for community to disclose stiffness modulus degradation with elapsed time, which is necessary for finite element numerical modelling. This manuscript aims to assess creep effect and derive calibration factor between global to local strains. Field monitoring strain readings of high-elongation gauges glued to geosynthetics must be calibrated against “true” global strain. Geosynthetics polyester (PET) geogrid types Fortrac 35T, 55T, 80T, 110T and 150T were examined at the machine direction under constant strain load ranged from 20% to 0.05% strain/min using the multi-rib tensile method. Correlation charts were plotted to predict stiffness reduction versus logarithm of time. The long-term stiffness value decreases in non-linear manner with increasing logarithm of time but after 1000 hours, is considerably constant of 75% of the secant modulus at 2% strain (working loads). Calibration factor between global to local strains ranged from 2.08 to 1.99 was measured at 2% strain, in agreement with comparable factor of 2.2, which was introduced by Allen et al. (2002). Calibration Factor values slightly increased as strain rate decreased.

Geosynthetics became one of the outstanding innovations with ever-growing significance for geotechnical and geo-environmental engineering industry. Earthwork construction over soft polluted sludge lagoons and tailing impoundments is mandatory to cap various waste materials. Low shear strength and high compressibility of such soil deposits expose short and long-term geotechnical challenges. Geosynthetics provide strengthening and allow accessibility over these deposits, which save money and reduce carbon footprint. Like all polymeric products, geosynthetics are susceptible to creep. However, creep data is not published by manufactures for community to disclose stiffness modulus degradation with elapsed time, which is necessary for finite element numerical modelling. This manuscript aims to assess creep effect and derive calibration factor between global to local strains. Field monitoring strain readings of high-elongation gauges glued to geosynthetics must be calibrated against “true” global strain. Geosynthetics polyester (PET) geogrid types Fortrac 35T, 55T, 80T, 110T and 150T were examined at the machine direction under constant strain load ranged from 20% to 0.05% strain/min using the multi-rib tensile method. Correlation charts were plotted to predict stiffness reduction versus logarithm of time. The long-term stiffness value decreases in non-linear manner with increasing logarithm of time but after 1000 hours, is considerably constant of 75% of the secant modulus at 2% strain (working loads). Calibration factor between global to local strains ranged from 2.08 to 1.99 was measured at 2% strain, in agreement with comparable factor of 2.2, which was introduced by Allen et al. (2002). Calibration Factor values slightly increased as strain rate decreased.