Geotechnical Properties Of Granulated Rubber And Loess Soil Mixtures

Automobile tires are becoming a large volume of solid waste that is prohibited to come into landfill site. China has been the first automobile producer and seller in the world since 2009. The problem of disposal scrap tires are seriously with the legislation of environment protecting and the legislation of discard as useless of automobile tires. Scrap tires problem is that scrap tires as the large volume solid waste regarding not easy land filled is a disposal problem worldwide. Some of the natural reused scrap tires such as tire-derived fuel for energy generation, remanufactured tires, high way crash barriers, low-grade rubber products et al. Although these recycling, reuse efforts consume 70% of scrap tires, there are still a large amount tires cannot be disposal correctly.Industrialized countries have been undertaking over thirty years in studying the possibilities of using tire shreds or tire-derived aggregates (TDA) as lightweight materials in civil engineering. Geotechnical research indicated that TDA possess some potential properties compared to natural soils, such as high durability, strength, thermal insulation capacity. This new kind of geomaterial is successfully used in highway embankments and backfills behind retaining structures over weak or compressible soils foundation.It is necessary to perform the research of using TDA or TDA-Soil mixtures (TDA-SM) in geotechnical application in our country. The thesis studies the geotechnical properties of scrap tires and loess mixtures in China firstly with referencing the achievement of scrap tires disposal in civil engineering in developed country. Using "waste" to solve rode structure problem while can exploit a new high-profile geotechnical material and a new way of scrap tires disposal.The physical and mechanical properties of TDA and TDA-SM are different from natural mineral soils, changing with the tire style, tire grain size, tire content, matrix property, compaction manner et al. This thesis focus on the mechanical property of granulated rubber and loess mixtures (GR-LM) through laboratory study including compaction test, compression test, direct shear test, and unconsolidated undrained triaxial test. The test data are analyzed based on the macroscopic mechanical phenomenon of binary packing mini-fabric, and the relationship between shear strength and mini-fabric was explained. The major results are as follows:1. Physical properties of GR-LMThe specific density and water absorption of granulated rubber were tested. The density of granulated rubber loess mixtures decreased with increasing rubber content, at a rate of approximately 0.78 kN/m3 per 10% rubber content by weight. The specific of granulated rubber is slightly higher than that of water, and the water absorption is neglect.2. Compactibility of GR-LMThe compactibility of GR-LM was studied by standard and modified Proctor tests. The result shows that with the range of 0% to 20% of granulated rubber content,GR-LM has a similar compactibility to that of loess, but the dry density and water content of mixtures have a less change when the granulated tires content is large than 40%. An effectiveness compaction were gained when the compaction performed of 30% granulated rubber under Proctor compaction energy, and compaction performed of 40% granulated rubber under modified Proctor compaction energy respectively.3. Compression properties of GR-LMCompression tests have been used to investigate the compressibility of granulated rubber and loess mixtures. The result indicated that the compression properties of mixtures are between the compacted loess and the compacted granulated rubber. The modulus of compressibility of the mixtures decreases with increasing granulated rubber content, while the coefficient compressibility elastic strain increases with increasing content. One of the main reasons in changing of compressibility of mixtures was interpartical contact structure. The elastic of granulated rubber causes an increase of low modulus of compressibility. It was considered that the property of modulus of mixtures varying with content could be used in geoengineering applications deal with deformation such as reducing load of culvert and dynamic stress release.4. Stress-strain and shear strength of GR-LMShear strength and stress-strain properties of GR-LM were investigated through direct shear test and unconsolidated undrained triaxial test. The effects on shear strength of varying confining pressure and rubber content w evaluated. It is found that GR-LM is stress-strain hardening behavior except for specimens of pure loess at low confining pressure. The test results showed no well-defined clear peak shear strength. The optimum granulated tire content (i.e., the one leading to the maximum shear strength) was about 30% at low and medium confined pressure (50-100kPa) in triaxial test. The optimum granulated tire content in direct shear tests was about 30% and 40% at Proctor compaction energy and modified Proctor energy respectively. Tests showed that the content of 30-40% was found to be sensitive to the shear strength of GR-LM under different confining pressure used in this study. The GR-LM with sensitive content shows high strength at low confined pressure (<100kPa) and hybolic, but shows nearly line deviatoric stress-strain behavior at high confining pressure (>200kPa). When the content of GR-LM are over 50% showed fully contractive volumetric strain behavior and nearly line deviatoric stress-strain behavior. The critical content of GR-LM is analyzed from the viewpoint of granulated rubber loess mixtures's meso-structure. By combination of porosity structure and loess matrix state, the influence of rubber content on the shear strength of compacted GR-LM was reasonably explained.5. Constitutive model of granulated rubber and loess mixturesThe hyperbolic model is relatively simple, well validated and it reliably represents soil behavior. Parameters of hyperbolic for granulated rubber loess mixtures were calculated using data derived from conventional triaxial compression tests. The comparison between the hyperbolic model and the laboratory data is performed and the suitability of hyperbolic model can be used for low rubber content (less than 30%) mixtures. The mixtures with 30-40% rubber content shows sensitivity of stress-strain to stress. The deviatoric stress-strain of 30-40% mixtures under low to middle stress (<200kPa) can be described with hyperbolic model, while under high stress the deviatoric stress-strain expresses nearly line variation. Stress-strain behavior of high rubber content mixtures and of pure granulated rubber can be described with elastic model.6. GR-LM as load reduction materials and design optimizedThe earth pressure over square culvert were tested incite. The results shows that the earth pressure on the top of the culvert with filled GR-LM is less than 30% compared with earth pressure of no mixtures over culvert. Numerical modeling performs the load reduction design over culvert of filling mixtures. The effects of load reduction are connected with rubber content of mixtures, position of mixtures, width and thickNess of mixtures. It has been derived that use GR-LM lined on the culvert can change the behavior of soil pressure distribution and settlement on the top and side of culverts. The load reduction of culvert is distinct.It has been found that granulated rubber and loess mixtures are fit to use in geotechnical engineering applications. The salient benefits of using GR-LM can solve problems with stress and settlement in geotechnical engineering. The benefits include reducing density of fill, adequate stability (with the rubber content of about 30-40% at low or middle confined pressure), variable modular (with different content of rubber and different pressure, the modular of mixtures are different).