Macroscopic mechanical behavior and microstructural evolution of compacted loess in the Chinese Loess Plateau

Abstract

Understanding the mechanical behavior of compacted loess is of great significance to engineering construction on the Loess Plateau. To gain an in-depth knowledge of the variations in compressibility, shear strength and microstructure of compacted loess at different dry densities and water contents, a series of macro and microscopic tests were carried out on the loess samples, including oedometer compression tests, direct shear tests and scanning electron microscope imaging. The pore properties of loess in microscopic images were investigated using the particle (pores) and cracks analysis system. The relationship between pore microscopic indicators and mechanical parameters was explored by multivariate statistical analysis. The results show that the compression coefficient of compacted loess decreases with increasing dry density, of which trend is more significant at high water content. Both cohesion and internal friction angle decrease with increasing water content, but the former is more sensitive to changes in soil moisture. Besides, the evolution sequence of compacted loess structure is basically overhead-mosaic-flocculation with the increase of compactness and saturation. The difference is that with the compaction, the pores in the loess sample change from macropores into mesopores and then to small pores, and the directional distribution and morphological complexity of the pores weakens; while with the humidification of the loess sample, small pores and macropores transform into mesopores, and the pores are more oriented and more complex in shape. During this process, the micropore content changes are weak. Moreover, mesopores content and pore fractal dimension have a positive effect on compressibility, while micropores content and orientation probability entropy have a positive effect on shear strength.