Marwan Hany
Settlement: As loads pass over the roadbed, the soil particles rearrange and compact, causing the layer thickness to decrease. This is permanent deformation. Settlement increases with higher loads, more passes, and weaker soil structure. Plastic deformation: If the loads exceed the maximum shear strength of the soil, the particles can slide past each other plastically. This destroys the original structure and strength. Repeated plastic deformation leads to failure. Loss of particles: Heavy and repeated loading causes soil particles to break apart or detach from the roadbed, resulting in loss of material and strength. Fine particles can also get washed away by water. Aggregate breakdown: Natural or added aggregates can breakdown under the impact and shearing forces. This leads to a loss of strength, increased settlement, and a denser, weaker structure. Cracks and crevices: Horizontal and vertical cracks, crevices and pockets form due to compressive and tensile stresses from loads and changes in moisture content. This allows for further settlement, water damage and loss of strength. Lean clay formation: Under the combined effects of compaction, wetting-drying cycles and sodium ion exchange, lightweight soils can convert to low-strength lean clays at the base of the roadbed. This clay has much lower shear strength and durability. Moisture damage: Variations in moisture content, especially repeated saturation and drying, cause swelling, shrinking and weakening of the soil aggregates and bonds. This accelerates other deformation and deterioration mechanisms. Proper drainage and moisture management can help control moisture-induced damage.
Lightweight soil roadbeds, like those made of organic matter, coal ash, slag, etc. tend to deform and fail over time under repeated traffic loads through several mechanisms:
To prevent excessive deformation and failure of lightweight roadbeds, techniques include: using reinforcing geosynthetics, limiting heavy loads, increasing thickness, improving moisture management, using cement or lime stabilization, and vegetation cover on slopes and shoulders. Periodic maintenance and regrading also help extend the service life.
Does this help explain the key mechanisms by which lightweight soil roadbeds deform and fail over time under repeated traffic loading? Let me know if you have any other questions!
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