Heterogeneous evolution of pore structure during loess collapse: insights from X-ray micro-computed tomography

The pore structure is an important feature of loess fabric and significantly influences the hydraulic properties. The evolution of pore structure during loess collapse has been extensively investigated but some aspects are still not well understood. In this study, the 3D pore structure evolution within the same loess sample was characterized using X-ray micro-computed tomography in combination with an in-house collapse test set-up. The loess pore space consists of two distinct pore categories: constricted pores and free pores. The former can be assessed only through smaller pores while the latter are generally channel-like in shape. We extracted constricted pores and free pores from the tomography images and our results show that they behave differently during the collapse. The constricted pores were not destroyed during the collapse and many of them maintain well their sizes and shapes. On the other hand, the channel-like free pores were typically closed up and had a more important contribution to the overall porosity reduction. Our results demonstrate that the pore structure evolution associated with loess collapse is not only related to pore size, but also closely linked to pore morphology (i.e. constricted/free pores). The outcome of this work provides new insights into the loess collapse process and serves to better understand the underlying mechanism of fabric collapse.