Laboratory study on properties of rubber-soils

Both the stability and settlement of embankments across soft soils can be improved by the use of lightweight engineered fill. This research investigates the feasibility of using rubber-soils, i.e., a blend of rubber chips and soils mixed in various proportions, in highway embankments as lightweight geomaterial, based on comprehensive laboratory testing and evaluations. The thesis contains: synthesis of all available information and results from laboratory testing of tire chips, rubber-Ottawa sand, and rubber-Crosby till. The engineering properties determined as part of this research, namely: index properties, compactibility, compressibility, shear strength, resilient modulus, and permeability, suggest that rubber-soils show significant promise for use in highway embankments. It is found that rubber-sand with chip/mix ratios of 38% or less possess excellent engineering properties: easy to compact; low dry density; low compressibility; high strength; and excellent drainage characteristics. This rubber-sand mix is recommended where significant settlements are unacceptable, e.g., bridge abutments, etc. The use of rubber-Crosby till mixes in embankments offer some technical benefits, like low dry density and good hydraulic characteristics. However, this material has high compressibility, low shear strength, and is difficult to mix/compact in the field. The resilient modulus values of rubber-soils are significantly lower than conventional subgrade soils. A recent field study reports that shredded tires show no likelihood of having adverse effects on groundwater quality. However, long term concerns under adverse environmental conditions still persist. A 3-ft soil cap and all-round soil cover is recommended for safety against fire risk and providing adequate confining pressure to reduce settlements and adverse effect of repeated traffic loads. The use of tire chips and rubber-sand in highway embankments, above the water table, is very promising and should be promoted. It is proposed that the strength and compressibility parameters determined as part of this research be used for design and also evaluation of embankments incorporating similar materials, until such time as more extensive testing results are available