SOIL REINFORCEMENT

Because of the recent rash of hurricanes like Katrina and tsunamis, we have become more aware of the need for protection against their violence. Geotextiles play a major role in this protection. Reinforced soil was used by Babylonians 3000 years ago in the construction of their pyramid-like tower, ziggurats. One of these famous towers, the Tower of Babel, collapsed. For thousands of years, the Chinese used wood, straw, and bamboo for soil reinforcement including the construction of the Great Wall. In fact, the Chinese symbol for civil engineering can be translated as earth and wood. The Dutch have made extensive use of natural fibrous materials in their age-old battle with the sea. The Romans employed wood and reed for foundation reinforcement. By the 1920s, cotton fabrics were tested as a... 

Many carpet manufacturers, fiber and chemical suppliers, recycling companies, and academic institutions are actively pursuing various methods to recycle fibrous waste. The approaches include chemical processes to depolymerize nylon and other polymers, recovery of plastic resins from carpet fibers, direct extrusion of mixed carpet waste, composites as wood substitutes, fibers for concrete and soil reinforcement, waste-to-energy conversion, and carpet as feedstock for cement kilns. 

Mwasha A (2009) Using environmentally friendly geotextiles for soil reinforcement a parametric study. Mater Des 30 1798-1803... 

The robust nature of earthwork constructions is likely to make material damage a more significant factor for soil reinforcement than for other applications of polymer materials, and therefore consideration should also be given to possible strength loss caused by installation damage. 

The three primary applications of soil reinforcement using geotextiles are ... 

John, N. (1987), Paulson geosynthetic material and physical properties relevant to soil reinforcement applications. Geotextiles and Geomembranes, 6,211-212. 

Collios, A., Delmas, P, Gourc, J. P. and Giroud, J. P. (1980), Experiments on soil reinforcement with geotextiles. Proceedings of Syrup Use of Geotextiles for Soil Improvement, ASCE, Portland pp. 53-73. 

The amount, distribution and placement of the instruments installed in the centrifuge models and the flexibility of the coimecting cables are carefully chosen to minimize the disturbance on soil behavior. In general, large concentration of instruments was avoided and cables were positioned so that soil reinforcement and creation of preferential flow paths was hampered. The loading of the model was carefully performed to minimize the 1-g vibrations induced in the model, which could affect the instruments position. 

Reinforced earth is a composite of soil and tensile- or shear-resistant inclusions that function through the agency of direct soil-reinforcement interaction to produce a material having a performance superior to that of soil alone. Reinforced earth may be used to replace conventional structures, to reduce area of land required, or to build flexible structures over poor or soft foundations. 

Concrete and soil are dealt with in great quantities in construction. Studies have shown that the properties of these materials can be enhanced by fiber reinforcement. A brief review is provided in this article on the advantages of fiber reinforcement of concrete and soil. Laboratory and field studies using carpet waste fibers for concrete and soil reinforcement are described. 

Carpet waste generated each year and accumulated in landfills represents a considerable potential resource, as it may be converted into various useful products The rate of carpet disposal is about 2-3 million tons per year in the US A, and about 4-6 million tons per year worldwide. A carpet typically consists of two layers of (i) backing (usually fabrics from polypropylene tape yams), joined by CaCOj filled styrene-butadiene latex rubber (SBR), and (ii) face fibers (the majority being nylon 6 and nylon 66 textured yams) tufted into the primary backing. To use post-consumer carpet (PCC) as concrete or soil reinforcement, the carpet is shredded to recover fibers. It is generally not necessary to disassemble yams in the carpet into individual fibers. The size-reduction process yields the following from PCC ... 

In the size-reduction process, some adhesive is removed and some still remains on the fibers. For both concrete and soil reinforcement, it is not necessary to completely remove the adhesive, avoiding the process of cleaning and separation. Therefore, carpet can be converted to fibers at very low cost for concrete and soil reinforcement. 

Carpet waste for soil and concrete reinforcement requires only a simple and inexpensive shredding process. For soil applications, virtually all types of carpet are suitable, and therefore sorting is not necessary. For concrete reinforcement, only nylon and polypropylene carpet should be used. It is also possible to mechanically remove nylon face fibers from a nylon carpet to produce nylon resins and use the less-valuable residual, composed of mostly polypropylene backing, for concrete and soil reinforcement. 

The use of carpet waste for soil reinforcement has been shown to increase the triaxial compressive strength and ductility of soil. Field trials showed that shredded carpet waste fibers (to 70 mm long) can be blended into soil with conventional equipment. The availability of low-cost fibers from carpet waste could lead to wider use of fiber reinforced soil and more cost-effective construction. 

Murray J., Frost J. D. and Wang Y. (2000), The Behavior of Sandy Soil Reinforced with Discontinuous Fiber Inclusions , Transportation Research Record, No. 1714, 9-17. 

---