Structural Characteristics of Natural Loess in Northwest China and its Effect on Shear Behavior

This paper presents the results of relationship between structure and shear behavior of natural loess collected from Northwest China. The shear performance was conducted by triaxial tests. Scanning electron microscopy (SEM) in conjunction with MATLAB were used to interpret the microstructure characteristics of soil samples before and after triaxial tests, and mercury intrusion porosimetry (MIP) was performed on investigation of pore size distributions. Based on the MIP results, the pore distribution of natural loess at initial state can be divided into micropore (< 0.03 μm), fine pore (0.03–5 μm), medium pore (5–11 μm) and macropore (> 11 μm), respectively. The shear behavior during triaxial tests shows that, soil samples exhibit obvious homogenous deformation and yielding hysteresis with the increase of confining pressure, which is well agreement with the microstructure evolution characteristics investigated by means of SEM and MIP. It is found that strength loss of loess soils can be mainly attributed to changes in particle arrangement, breaking up and corresponding pore size variation. Quantitative and qualitative statistics analysis of soil particles and pore types shows that there is a negative relationship between confining pressure and parameters characterizing particle morphology, as well as between pore area and deviating stress. Although the structure of loess differs from region to region, the relationship between structural parameters and confining pressure or deviator stress can be used to estimate the influence of structure on shear behavior.