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Volume 109
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Experimental investigation into the role of particle morphology in the strength and dilatancy behaviour of aeolian dune sand
Shiva Prashanth Kumar Kodicherla a *, Minyi Zhu b, Kamoca Fernandes a, Darga Kumar Nandyala c, Naveen Revanna d
a Department of Civil, Mining and Process Engineering, Namibia University of Science and Technology, Windhoek, Namibia
b Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai, China
c Department of Civil Engineering, JNT University Hyderabad, Kukatpally, Hyderabad, Telangana State, India
d Department of Civil Engineering, Dr Ambedkar Institute of Technology, Bengaluru, India
10.1016/j.partic.2025.12.012
Volume 109, February 2026, Pages 165-179
Received 30 October 2025, Revised 11 December 2025, Accepted 17 December 2025, Available online 2 January 2026, Version of Record 8 January 2026.
E-mail: prashanthetc1024@gmail.com; skodicherla@nust.na
Highlights

• Normalised shear stress is stable across densities; strains depend on packing.

• Peak and critical friction angles rise with density; dilation underpredicted.

• Results confirm morphology controls strength and dilatancy characteristics via microstructure.


Abstract

This study investigates the role of particle morphology in the strength and dilatancy behaviour of Namibian dune sand under direct shear test (DST) conditions. For this purpose, a series of DSTs were performed under three normal stresses (50, 100, and 200 kPa) and three relative densities (0.25, 0.5, and 0.75). To understand the role of particle morphology, the particle shape descriptors, including aspect ratio, roundness, convexity, sphericity, and overall regularity, were quantified from two-dimensional binary images derived from scanning electron microscopy using a computational geometry approach considering the major plane of orientation. Results indicate that the stress ratio exhibits strain-hardening followed by softening in dense assemblies, while loose assemblies display continuous hardening. The vertical strain and dilatancy angle decrease with increasing normal stress, whereas peak friction angles rise with relative density due to enhanced particle interlocking; critical state friction angles remain largely insensitive to density, reflecting stabilisation at ultimate shearing. Bolton's empirical model underestimates dilatancy angles, which are highly sensitive to normal stress (empirical constant, Q ≈ 10.47 at 200 kPa). The critical state parameters in the void's ratio – logarithm of normal stress normalised by atmospheric pressure plane vary systematically with density and particle regularity, aligning with literature and confirming the robustness of the proposed framework. These findings validate constitutive predictions and underscore the pivotal role of particle morphology in controlling sand strength and dilatancy, offering insights for physically grounded constitutive modelling of granular materials.

Graphical abstract
Keywords
Namibian dune sand; Particle morphology; Shear strength; Stress-dilatancy; Critical state
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