Abstract
The cost of retaining structures used for the lateral support of roadside embankments can be significantly reduced through the use of lightly cemented mixtures of expanded polystyrene (EPS) beads and backfill soils as lightweight roadside embankment material. Four grades of residually derived sandy soils were mixed with EPS beads and the geocomposites were stabilised with 3% cement content, compacted and cured. The textural properties and shear strength parameters of dry and soaked specimens of the cemented geocomposites were determined by direct shear tests. The shear parameters and slope stability charts were used to simulate the slope of typical road embankments. The settlement potentials at different applied normal stresses were also determined. Inclusion of EPS reduced the dry density of the residual soils from an average value of 1790 kg/m3 to 1335 kg/m3. The maximum friction coefficient, tan ᴓ′, mobilised by the geocomposite specimens decreased with an increase in the soil fines content (>0.425 mm). The difference in tan ᴓ′ between the stabilised geocomposites and the natural soil was also dependent on the fines content. For an embankment height of 20 m, slope angles of 38° and 62° were determined for fine sand geocomposites in fully saturated drainage and drained conditions, respectively. Lower slope angles were determined for geocomposites made from silty, coarse and gravelly sands. A limiting embankment height of 50 m was determined for the four geocomposites. Rainfall-induced settlement of geocomposites was dependent on pre-inundation stiffness; for the range of applied stress up to 200 kPa, the settlement exhibited by the fine and silty sand geocomposites was lower than that for the coarse and gravelly sand geocomposites. Fine and silty sands make poor materials for slope embankments because of their poor hydraulic conductivity; however, fine and silty sand geocomposites have a good conductivity and friction angle to support slope embankments.
Highlights
The cost of road construction can be reduced significantly when the backfill materials used for the preparation of the road subgrade, subbase and side embankments are constructed using soil and road materials that exist along the designated roadway
The mixture was blended with 30% by volume of expanded polystyrene (EPS) beads and water and compacted in the mould to determine the effect of EPS proportion on the optimum moisture content and dry density of cement-stabilised backfill materials
The inclusion of EPS and 3% cement resulted in a 20% reduction in dry density and marginal reduction in shear strength when soils with less than 20% fines were used for the production of the geocomposites
Summary
The cost of road construction can be reduced significantly when the backfill materials used for the preparation of the road subgrade, subbase and side embankments are constructed using soil and road materials that exist along the designated roadway. In most parts of the tropical and subtropical regions of the world, residual soils are frequently encountered along most proposed roadways. It may be difficult to predict the type of foundation required when a residual soil is encountered.[1,2] Residual soils can be recompacted to high density in situ, and are known to mobilise high shear strength when dried, but can soften significantly when wet or poorly drained. Embankments constructed with residual soils often require cement stabilisation and a retaining structure to limit or prevent roadside embankment slope failure, especially upon inundation
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