Purpose <p>The pore structure stability of barrier material governs its long-term remediation efficacy in contaminated sites and landfills. However, contaminant erosion alters pore architecture, increasing environmental recontamination risks via secondary pollutant release. While soil pore evolution under prolonged contamination has been investigated, existing studies focus on conventional parameters (e.g., pore distribution), lacking a systematic analysis of critical non-conventional characteristics like pore morphology, thus limiting long-term remediation efficacy accurately assessment.</p> Materials and methods <p>Based on this, this study employs time as an influential variable, focusing on diesel-contaminated bentonite barrier materials. By integrating mercury intrusion porosimetry (MIP) and X-ray computed tomography (CT) for pore structure analysis, and employing Avizo three-dimensional visualization software, it dynamically monitors the evolutionary characteristics of pore structures in contaminated soil to reveal dynamic pore morphology evolution mechanisms under diesel aging effects. Simultaneously, through laser particle size analysis, gas chromatography-mass spectrometry, and ammonium saturation methods, combined with multidimensional investigations of particle gradation, micromorphology, diesel adsorption capacity, pH value, cation exchange capacity, and X-ray diffraction phase analysis, it systematically elucidates the mechanistic principles governing pore morphology evolution.</p> Results and discussion <p>Analysis of pore size distribution evolution reveals that prolonged diesel contamination reduces both inter- and intra-aggregate porosity in soils, triggering overall shrinkage with axial heterogeneity—end regions exhibit greater porosity reduction than central zones. Pore systems undergo radial deflection (150° to -150°), correlating with soil contraction (30° to -30°). The mean pore shape factor decreases from 1.32 (7 days) to 1.09 (120 days), characterizing systematic declines in elongated pores and marked increases in elliptical/spherical pores. Dynamic monitoring identifies localized pore collapse as a geometric alteration mechanism induced by diesel aging. Concurrently, diffusion-adsorption-precipitation of diesel components on montmorillonite surfaces and acid-base neutralization bentonite interlayer spacing, disintegrating flocculent structures and redistributing particles, ultimately driving multiscale morphological evolution in pore size distribution.</p> Conclusions <p>Thus, long-term diesel contamination induces non-proportional local pore collapse and directional deflection in soils, with surface property changes of soil particles governing pore size distribution and morphological evolution. This study systematically reveals the dynamic evolution mechanism of pore morphology in bentonite barriers under organic pollution and providing a basis for improving accurate long-term performance assessment of containment walls in contaminated sites and landfills.</p>