Quantification of the pore structures of Malan loess and the effects on loess permeability and environmental significance, Shaanxi Province, China: an experimental study

Abstract

The pore microstructures of loess control the porosity and permeability of the loess, affecting the patterns of groundwater flow and the transport of contaminants. In the present study, the pore microstructure of Malan loess was investigated quantitatively in samples from five different loess layers. Specimens were examined via SEM, and pore microstructure parameters were determined using the digital image analysis method. Pore structures (including pore area ratio (PAR), pore size distribution, pore shape and pore morphology), the effects of the pore structure on loess permeability and the environmental significance of these factors are discussed in this paper. The results indicate that the samples of five loess layers in this study are considered to be porous soil, according to both the PAR and porosity values. The number of micropores, small pores, mesopores and macropores decreased significantly. The differences in number were mainly due to the significant reduction in the number of round pores, indicating that round pores tend to be small. In terms of area, micropores, small pores, mesopores and macropores were dominated by elongated and irregular pores. The macro- and mesopore structural characteristics of loess determined the transfer characteristics of groundwater and pollutants in the loess. Additionally, the 62% area reduction in the area of elongated or irregular macro- and mesopores and the decreasing connectivity from top to bottom layers caused by the deformation and destruction of the pores due to the overlying soil reduced the permeability and the water/pollutant migration rate with depth.