Microscopic and mechanical properties of undisturbed and remoulded red clay from Guiyang, China

Yanzhao Zhang,Shaoyun Pu,Rita Yi Man Li,Jing Zhang

doi:10.1038/s41598-020-71605-7

Abstract

Unconsolidated-undrained (UU) tests were conducted to investigate the mechanical and morphological properties of undisturbed and remoulded red clay, with the microscopic characteristics determined by scanning electron microscopy (SEM). The microanalysis showed that the red clay aggregate was granular, curved-slice and thin layered and flower-shaped ellipsoid, with X and Y-type cracks and pores in the undisturbed red clay. Moreover, the contact modes of red clay aggregates were point contact, line contact, surface contact and mosaic contact. In addition, the main microstructure red clay was flocculation, honeycomb and pseudosphere structures. The pores in undisturbed soil were arranged in one direction, with no obvious directionality in remoulded red clay. The pore area, perimeter and maximum length of undisturbed red clay were smaller than those of remoulded red clay, with a larger probability entropy, probability distribution index and fractal dimension of pore distribution of undisturbed red clay than remoulded red clay. UU tests showed that the shear strength of undisturbed red clay was higher than that of remoulded red clay.

Highlights

Unconsolidated-undrained (UU) tests were conducted to investigate the mechanical and morphological properties of undisturbed and remoulded red clay, with the microscopic characteristics determined by scanning electron microscopy (SEM)
Red clay has a high water content, high void ratio and high plasticity, high bearing capacity, low compressibility and good engineering mechanical properties[3], so it is used as the filling material for the bearing layer of building foundations
It is important to analyse the mechanics of remoulded and undisturbed red clay to determine the differences in the m icrostructure[4]

Summary

Introduction

Unconsolidated-undrained (UU) tests were conducted to investigate the mechanical and morphological properties of undisturbed and remoulded red clay, with the microscopic characteristics determined by scanning electron microscopy (SEM). Zhou et al.[13] extracted the skeleton form, connecting substance and filling substance of the mentioned-above four structures to form the “grain” structure model of red clay In this model, the micro-skeleton of red clay comprises several different shaped “grains” with each grain composed of numerous different shaped clay particles cemented together by crystallised strong binding water and numerous fine free iron oxides on the surface of clay particles in the form of particles or films[13], while the "grain" is connected with other grains by the cohesion of strong and weak bound water, van der Waals forces, mutual electrostatic attraction and colloidal bonding force. The grain is a basic unit formed by mutually cemented clay particles with crystallised strong bound water, free iron oxide and other substances. The high strength and low compressibility of red clay are mainly due to the cementation formed by free iron oxide and the special connection between particles[15]

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Conclusion