Effect of reinforcement parameters on the mechanical behaviour of geosynthetic reinforced sand

Abstract

Soil possesses very high strength in compression, but virtually no strength in tension. Hence, when used as a construction material in civil engineering applications, soil usually fails in shear. Soil can be reinforced with foreign materials to form a composite material that has increased shear strength and some apparent tensile strength. Geosynthetics have proven to be among the most versatile, cost effective materials compared to all other alternatives of ground improvement, besides being more resistant to corrosion and chemical reactions. As a result, earth structures reinforced with geosynthetics are being constructed worldwide with increased frequency, even in permanent and critical applications. In this thesis, the effects of various reinforcement parameters-such as tensile strength of the geosynthetic material, surface roughness of reinforcement, quantity of reinforcement, reinforcement layout scheme, and form of reinforcement-on the mechanical behaviour of geosynthetic reinforced sand are studied. Since geosynthetic reinforced soil predominantly utilizes dry, cohesionless soils as backfill because of their high strength characteristics, good drainage properties, and higher bond with reinforcement, all experiments in this thesis used dry sand as the reinforced medium. A systematic series of undrained triaxial compression tests was conducted on dry sand reinforced with three different types of geosynthetics, in four types of layer configurations, three different forms, and five reinforcement layout schemes. The reinforcement types used were:

woven geotextile geogrid polyester film

The four layer configurations were 2, 3, 4, and 8 horizontal reinforcing layers in a triaxial specimen. The three different forms used were:

planar layers geocells randomly distributed discrete fibres

All forms used the same quantity of reinforcement. The results from triaxial tests were analysed to compute the apparent cohesive strength imparted to the soil due to geosynthetic reinforcement with varying reinforcement parameters. From the triaxial tests, it is found that geosynthetic reinforcement imparts apparent cohesive strength to otherwise cohesionless sand. The magnitude of apparent cohesion increases with:

increase in tensile modulus of the geosynthetic material increase in surface roughness due to penetration of sand particles reinforcement form reinforcement layout scheme

Several important conclusions were drawn regarding the cohesive strength of reinforced sand in terms of reinforcement type, amount, form, and layout. The effects of indent formation and surface roughness were studied through special triaxial tests, microscopic imaging, and surface roughness tests on reinforcing elements before and after testing. For the same amount of reinforcement, geocells were found to be the most effective in improving strength. The discrete fibre form of reinforcement was found to be inferior compared to planar and cellular forms in improving the stress–strain behaviour of sand. Among the layout schemes tested, equally spaced full length layers gave the highest efficiency. A simple composite model was developed to simulate the stress–strain behaviour of geosynthetic reinforced sand using experimental results based on an equivalent continuum approach. Numerical analyses using the program Fast Lagrangian Analysis of Continua (FLAC) with the experimentally developed composite model were found to capture the mechanical behaviour of geosynthetic reinforced sand reasonably well.