Finite Element Modelling of Rigid Pavement Slabs Subjected to Wheel Loading on Untreated and Treated Expansive Subgrade: A Parametric Study using PLAXIS 2D

Abstract

This parametric study investigates the structural behaviour of rigid pavement slabs resting on treated and untreated expansive subgrades. The research analyses the response of the pavement system when subjected to critical wheel loading applied at both the edge and interior zones of the slab. The parametric variations evaluated include a range of wheel loads (50Kn, 80kN, 100Kn) cross analyzed with various slab thicknesses (150mm, 200mm, 250mm, 300mm). Two-dimensional numerical modelling was executed using PLAXIS 2D software to compute and evaluate total deformation across all configurations. The numerical outcomes reveal that the treated subgrade significantly minimizes structural displacement, achieving a maximum deformation reduction of 43.04% at the slab edge and 42.20% at interior compared to the untreated subgrade. Ultimately, the results highlight the effectiveness of subgrade treatment in minimizing structural displacement optimizing slab design under heavy load distributions.

Introduction

The text presents a numerical investigation of rigid pavement performance over expansive soil using PLAXIS 2D finite element modelling. The study focuses on how slab thickness, wheel-load magnitude, loading position, and subgrade stabilization affect stresses and deformation.

Background

Rigid pavements have high load-carrying capacity and durability, but their performance depends strongly on the supporting subgrade. Expansive soils are particularly problematic because they swell when wet and shrink when dry, producing deformation and stresses that can damage concrete pavement slabs.

The pavement system considered includes:

• Concrete rigid pavement slab

• Dry Lean Concrete (DLC) layer

• Granular Subbase (GSB) layer

• Compacted subgrade

• Natural expansive subgrade

These intermediate layers help provide a uniform and stable platform, improve subgrade support, and reduce pavement distress.

Objectives

The study aims to:

1. Develop PLAXIS 2D numerical models of rigid pavement–soil interaction.

2. Evaluate stress distribution and total deformation under static wheel loads.

3. Study the effects of different slab thicknesses, wheel loads, and subgrade stiffnesses.

4. Quantify the improvement obtained through subgrade stabilization.

Literature findings

Previous finite element studies show that:

• FEM can capture pavement stresses and deformations more accurately than some conventional analytical approaches.

• Increasing slab thickness generally reduces flexural stress and vertical deformation.

• Expansive-soil swelling can generate significant stresses and pavement cracking.

• Chemical stabilization and geosynthetic reinforcement can improve subgrade strength and reduce deformation.

• Subgrade stiffness has a strong influence on pavement response.

• Edge loading can be particularly critical because support conditions are less uniform near pavement boundaries.

• Advanced nonlinear numerical modelling is useful for studying differences between edge and interior loading conditions.

The literature therefore supports examining slab thickness, load magnitude, loading location, and subgrade treatment together.

Numerical modelling

A 2D axisymmetric PLAXIS model is used to simulate the pavement system. The analysis considers:

• Slab thickness: 150–300 mm

• Wheel loads: 50, 80, and 100 kN

• Loading locations: interior and edge

• Subgrade conditions: treated and untreated

The model domain extends approximately 5.75 m horizontally and 8 m vertically to minimize boundary effects.

Pavement structure

The model represents several layers with different mechanical properties:

• Concrete slab

• 150 mm DLC

• 150 mm GSB

• 0.5 m compacted subgrade

• Natural subgrade extending below the pavement

The treated subgrade is assigned higher strength and stiffness than the untreated/natural expansive soil, allowing the study to quantify the benefit of stabilization.

Wheel-load modelling

Because the analysis uses an axisymmetric model, the rectangular tire contact area is converted into an equivalent circular contact area.

For a tire footprint of 0.3 m × 0.22 m, the equivalent circular radius is approximately 0.145 m. The resulting contact pressures for the three wheel loads are approximately:

• 50 kN: 0.758 MPa

• 80 kN: 1.212 MPa

• 100 kN: 1.515 MPa

This allows the wheel load to be applied consistently within the axisymmetric finite element model.

Model execution 2D approach provides a numerical means of assessing localized

The pavement and soil are represented primarily using the Mohr–Coulomb constitutive model. A medium finite-element mesh is used, with additional refinement around the pavement interfaces and wheel-contact region where high stress and deformation gradients are expected.

The analysis follows staged construction:

1. Establish initial geostatic stresses.

2. Activate pavement layers.

3. Apply wheel loading.

4. Evaluate stress and deformation responses under the different parametric conditions.

Conclusion

The principal conclusions derived from this parametric numerical investigation are presented below: 1) The free edge yields a peak deflection of 13.070 mm under an untreated 100kN load, which is 321% higher than the interior deflection of 3.102 mm. 2) Increasing slab thickness from 150 mm to 300 mm decreases displacements by 52.59% at the edge and 33.72% at the interior. 3) Subgrade treatment reduces interior deformation by up to 48.61% for a 300 mm slab, retaining a 46.05% reduction efficiency at 100kN. 4) Stabilized subgrade limits peak edge displacement to 3.360 mm, achieving a 45.77% deformation reduction under the maximum 100kN load. 5) Minor efficiency drops at higher loads confirm that increased axle weights project deep stress bulbs beyond the stabilized soil envelope.

References

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Copyright

Copyright © 2026 Chelluboina Satyasri, Dr. G.V.R Prasad Raju. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.