InterPore2025

Pore Structure Evolution in Clays Under Drying and Wetting Cycles: Insights from Mercury Intrusion Porosimetry

22 May 2025, 09:50

15m

Oral Presentation (MS04) Swelling and shrinking porous media MS04

Speaker

Mr Mohd Sameer Alam (Indian Institute of Technology Kanpur)

Description

The evolving pore structure in soil, influenced by various physico-chemical activities such as erosion, climate change, mechanical loading, and chemical weathering, can lead to catastrophic events like landslides and slope failures. One significant factor contributing to pore structure changes in soil is the cyclic drying and wetting process, which profoundly impacts various soil properties. Clayey soil minerals, particularly kaolinite and bentonite, play a crucial role in these failures. The evolving pore structure of these clayey soils under varying environmental conditions, such as drying and wetting cycles, significantly influences their permeability, strength, and overall hydro-mechanical behavior. However, experimentally capturing this pore evolution is challenging due to various microstructural disturbances associated with different experiments. This study discusses an experimental protocol that employs Mercury Intrusion Porosimetry (MIP) to quantify the pore structure evolution of kaolinite- and bentonite-rich soils. The rearrangement of soil particles due to drying and wetting cycles may lead to clogging or alterations in pore shape, particularly in smaller pores, thus reducing their connectivity. These smaller pores are particularly crucial for water retention, so any structural changes can influence the soil's ability to hold and transmit moisture, impacting its hydraulic properties. Conversely, larger pores may collapse during drying, reducing their capacity to hold water. This study analyzes the pore sizes of kaolinite and bentonite soils under various drying and wetting cycles using MIP and Scanning Electron Microscopy (SEM). Since the oven-drying method relies on evaporation and can cause alterations in pore structure, the freeze-drying procedure is preferred to preserve the natural pore structure. This study also includes a comparative analysis of pore structure changes induced by oven-drying and freeze-drying methods. A pore structure evolution model (Equation 1), proposed by Li et al. (2023), has been adopted to evaluate the evolution of pore structure under different drying and wetting cycles. The bimodal pore size distribution function (PSD) at the final state, flog(d) is utilized to model the pore size distribution derived from MIP results.

Equation 1

The evolution parameter, calibrated using the PSD, provides insight into how the pore structure changes during the drying and wetting processes.

Figure 1a,b

The SEM image in Figure 1(a) shows the microstructural features of freeze-dried Bentonite soil, revealing intricate pore networks and particle arrangements. The freeze-drying process preserves the natural pore structure, minimizing collapse or alteration caused by water removal. Figure 1(b) illustrates the PSD of bentonite soil, comparing freeze-dried (FD) and oven-dried (OD) samples at 46% water content using MIP. The PSD curve indicates that the freeze-dried sample exhibits a higher proportion of smaller pores, while the oven-dried sample shows a shift towards larger pores, reflecting structural changes due to thermal drying. These observations underscore the significant impact of drying methods on pore structure, with potential implications for soil-water interactions and retention behaviour.

Reference:
K. Peng Li, Y. Gui Chen, W. Min Ye, and Q. Wang, “Modelling the evolution of dual-pore structure for compacted clays along hydro-mechanical paths,” Computers and Geotechnics 157 (2023) 105308, https://doi.org/10.1016/j.compgeo.2023.105308