Structural Analysis of Two Flexible Pavements Subjected to Groundwater Table Rising Considering Unsaturated Behaviour of Subgrade Soil

Abstract

In flexible pavements, the resilient modulus (RM) of the subgrade layer is crucial for ensuring the serviceability of these structures throughout their lifespan. This research presents a 3D numerical analysis of the two most commonly used flexible pavement structures in the Algerian road network, GB/GB and GB/NTG, considering the effect of subgrade RM vulnerability to groundwater table (GWT) fluctuations. The first pavement structure is Gravel-Bitumen/Gravel-Bitumen (GB/GB), and the second is Gravel-Bitumen/Non-Treated-Gravel (GB/NTG), denoting the materials composing the base and subbase layers, respectively. To investigate pavement-subgrade interaction, four GWT levels (120m, 60m, 30m, and 15m) were used to assess the structural performance of the analyzed flexible pavements taking into account the effect of the unsaturated behavior of the subgrade soil subjected to GWT rises from 120m to 15m depth. Based on the conditions outlined in the Algerian Manual for New Pavement Design (AMNPD), the numerical simulations were conducted using the advanced FLAC3D software. The results of computed von Mises stresses and induced deflections indicated that the loss of suction, due to GWT rise, can impose substantial additional loads on pavement structures. Further analysis using Alize-LCPC software revealed that a Groundwater Table rise from 120m to 15m could reduce the service duration by over 11 years for GB/GB and over 14 years for GB/NTG pavement structures. Moreover, regression models were developed to predict deflection and von Mises stresses with reliable accuracy (R² > 0.90). Regardless cost considerations, the study concludes that the GB/NTG pavement structure outperforms the GB/GB pavement structure in terms of durability and performance considering similar scenarios.