Abstract
To investigate the microstructure of paleosol and its expansion characteristics, the paleosol of the Zaosheng #3 tunnel of the Yinxi high-speed railway was studied. Based on X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), nuclear magnetic resonance (NMR), and scanning electron microscopy techniques (SEM), the microstructure of the paleosol was analyzed in terms of the mineral composition, formation elements, pore structure, and particle morphology. Five groups of undisturbed and remolded soils with different moisture contents were tested for the unloaded expansion rate and loaded expansion rate. The results show that the mineral components of the paleosol are mainly quartz, potash feldspar, calcite, and hematite, with the highest-content-component quartz accounting for 45.4% of the total content; the clay mineral composition of the paleosol has the highest content of montmorillonite at 12.3%. The elemental composition of the paleosol is dominated by Al, Si, Ca, and Fe, which form expansive mineral components such as quartz and montmorillonite, creating inherent conditions for expansibility of the paleosol. The T2 distribution curves of the undisturbed and remolded paleosol are composed of three peaks. The pore distribution of paleosol mainly includes medium pores, followed by large pores, and the contents of small pores and superlarge pores are very small. In terms of particle contact, the undisturbed soil is mostly in the form of “surface-surface” and “surface-edge” contact, and the remolded soil is mainly in the form of “point-surface” and “point-point” contact. The unloaded expansion rate of remolded soil is approximately twice that of undisturbed soil. The rate of loaded expansion of both soils decreases with increasing moisture content.
Highlights
In the 21st century, with the rapid development of China’s economy, the construction of some large-scale geotechnical engineering projects has ushered in a new wave of development
With the development of imaging technology, many microscopic testing techniques have been applied to quantitative analysis of soil microstructures to deepen the understanding of soil microscopic properties, including scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX)
XRD can be used to analyze the crystal structure and mineral composition of soil masses based on the interference principle in optics [23, 24], and EDX can be used to study different constituent elements and their distribution in soil masses [25, 26], both of which are useful in the study of contaminated soils, with more applications in research
Summary
In the 21st century, with the rapid development of China’s economy, the construction of some large-scale geotechnical engineering projects has ushered in a new wave of development. One of the “ten longitudinal and ten transverse” integrated transport channels of China’s “13th Five-Year Plan” modern integrated transportation network is the Yinxi high-speed rail (Yinchuan-Xi’an) Because it passes through a large area of expansive paleosol group, the project since its construction has attracted the attention of geotechnical experts. Wu Yuntao et al [7] explored the deformation mechanism of paleosols under different stress paths by conducting triaxial shear tests and studied the changes in soil pores under different stress paths by nuclear magnetic resonance (NMR). With the development of imaging technology, many microscopic testing techniques have been applied to quantitative analysis of soil microstructures to deepen the understanding of soil microscopic properties, including scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). EDX, SEM, and NMR are used, and the results are combined with the existing research results of the author’s research group on paleosol. e changes in the microstructure characteristics and expansion characteristics of the undisturbed and remolded soil samples are explored, and explanation of the expansion mechanism based on the elements, mineral components, and microstructure of the soil is attempted to provide a reference for paleosol engineering
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