Mechanical Performance of Expansive Clay Subgrades Under Heavy Compaction and Soaked Loading Conditions

Expansive clay subgrades are highly moisture-sensitive, and their mechanical response under saturated conditions often governs the performance of flexible pavements and thickness design. This study experimentally evaluates the short-term mechanical performance of an untreated, remoulded expansive clay compacted with high compaction energy and tested under soaked loading conditions. Laboratory testing was carried out according to relevant Indian Standards and comprised of Modified Proctor compaction (IS 2720 Part 8), soaked California Bearing Ratio CBR testing after soaking for 96 h at 2.5 kg surcharge (IS 2720 Part 16), and unconsolidated-undrained UU direct shear testing as three runs to add normal stress. The results of the Modified Proctor tests showed a well-defined compaction peak: Maximum Dry Density (MDD) = 1.780 g/cm3 at Optimum Moisture Content (OMC) = 17.80%. The soil under saturated conditions showed low penetration resistance, with CBR = 4.96% at 2.5 mm and CBR = 3.86% at 5.0 mm, indicating that the saturated bearing capacity is limited under stable, ductile load penetration. UU direct shear response showed progressive mobilisation of shear resistance with increasing confinement, with peak shear stress increasing from approx 0.54 kg/cm2 (Run 1) to 0.80 kg/cm2 (Run 2) and 0.94 kg/cm2 (Run 3). The MohrCoulomb failure envelope was linear in the stress range tested, yielding shear. strength c = 0.36 kg/cm2, ph = 21.9deg (shear strength parameters given in kg/cm2 consistent with laboratory output). Overall, the sum of the results suggests that the shortterm shear behaviour of the soil is predictable, while the soaked bearing resistance is mechanically limiting the soil and thus strength-based parameters of the soil (soaked CBR and shear parameters) may be used to select between pavement thickening and subgrade improvement/stabilisation in moisture-prone service conditions.