Experimental and Numerical Investigation of Mechanical Behaviour of Expansive Soils under Cyclic Drying-Wetting Beneath Pavements

Abstract Expansive soils exhibit considerable volumes changes in response to humidity fluctuations, swelling upon water absorption and shrinkage during desiccation. This recurrent volumetric instability can induce differential settlements, often resulting in structural distress such as cracking in lightly loaded constructions. This study aims to analyse the behaviour of expansive soils under shrink-swell cycles by means of direct shear tests, oedometer tests and finite elements analysis. Hereby, number of cyclic drying-wetting of N=0, N=1, N=2, N=3, N=4, N=5, N=6, N=7, N=8 was investigated for more 200 undisturbed expansive soils from 6 locations in the study area. The soil samples exhibited a pronounced volumetric expansion of approximately 10% during the first two drying–wetting cycles. Beyond this stage, the swelling amplitude progressively diminished with each subsequent cycle, stabilizing at about 1% by the eighth cycle (N = 8). However, the shrink magnitude increased approximately from 10% to 50% as the number of swell-shrink increases. extent of cracking progressively increased with the number of swell-shrink cycles, resulting in an enlargement of the mesopore volume within the samples. Results from the direct shear tests performed under unconsolidated–undrained (UU) conditions showed that both the angle of internal friction and the cohesion underwent a pronounced reduction during the first two cycles. Thereafter, these parameters converged toward residual values corresponding to approximately 30% and 35% of their initial internal friction angle and cohesion, respectively. Exponential decay functions are derived from the test data, that describe the degradation of the shear strength, the angle of internal friction and the cohesion with increasing numbers of drying–wetting cycles. Furthermore, a finite element model has been developed by means of the software Abaqus for analysing the response of pavement resting on expansive soil under to repeated shrink-swell. The finite elements model has been validated with the in-situ results of falling weight deflectometer. The numerical results demonstrated that the pavement deflection and shear strain increase with increasing cyclic drying-wetting. As a result, cracks can occur in the pavement and compromising the serviceability limit state and the integrity of the pavement structure.