A Laboratory Experimental and Numerical Investigation of Water Infiltration in Burned Soils

Wildfires may significantly alter the mineralogical and microstructural characteristics of geological materials, leading to increased susceptibility to landslides, debris flows, and other related hazards. These processes may involve considerable post-fire hydrological changes that affect the infiltration rate and the surface runoff in the burned soils. In the present study, a laboratory experimental investigation is carried out focusing on the water infiltration in burned soils which were produced in a muffle furnace at accurately controlled temperatures within 400 °C∼800 °C. The original and burned soils were first subjected to a number of geotechnical tests, including grain size distribution, consistency, and hydraulic conductivity. Subsequently, their water infiltration rates were measured in a laboratory setup. Finally, numerical simulations are performed to assess the infiltration process based on the Green–Ampt model. The experimental results reveal significant differences in the hydrological behavior between burned and unburned soils. Overall, burned soils experienced quicker ponding and slower infiltration. However, as the burning temperature increased from moderate to high, the infiltration rate also rose considerably, along with delayed ponding time. This trend may be related to the microstructural change in the grain size distribution explored experimentally in the present study. The numerical results are highly consistent with the experimental data. The hydraulic conductivity is identified as the predominant parameter in the infiltration process examined and simulated in the present study. Its evolution with varied burning temperatures can also be traced to the fire-induced alteration in the grain size distribution, and primarily accounts for the differences in the infiltration of different soil specimens. The present study demonstrates the potential of laboratory experiments complemented with a quantitative modeling approach in improving our understanding of soil’s post-fire hydrological responses.