The impact of soil sample shrinkage on the soil–water characteristic curve obtained by centrifugation test: insights based on microstructural changes

• A quantitative analysis was conducted on the shrinkage of soil samples in the process of determining SWCC through centrifugation. • Soil shrinkage alters the particle contact mechanism and pore structure of soil, resulting in deviations in the centrifugation results of SWCC. • A normalized grey correlation coefficient r k and a correction coefficient λ were defined to describe and quantify the impact of changes in microscopic pore parameters on the suction waterhead. • A PCM model was proposed to correct the deviations in the centrifugation results of SWCC. The main difficulty in understanding the deviations in the soil–water characteristic curve (SWCC) obtained by centrifugation test is to elucidate the response of soil sample shrinkage to the microscopic pore structure during the centrifugation process. To reveal the intrinsic mechanism of this effect, clay samples with varying compaction degrees were prepared and their SWCC results were obtained through centrifugation. Then, the influencing mechanism of soil shrinkage on the SWCC results was elaborated according to the macroscopic and microscopic structural changes of soil samples before and after the centrifugation and further, a novel model for correcting the deviations in SWCC results was proposed based on the changes in microscopic pore parameters. The results indicate that significant changes occurred in the particle contact mechanism and topological relationship of the pore network in the soil samples after centrifugation, manifesting as a significant increase in fractal dimension and pore tortuosity, and a reduction in pore throats and pore radius. Consequently, a less connected, less even pore network was formed, resulting in changes in soil hydraulic properties. Further, a model for correcting the centrifugation results of SWCC based on the changes in microscopic pore parameters was established. Results of a series of comparative verifications demonstrate that the proposed correction model can accurately correct the deviations in SWCC results caused by soil shrinkage in centrifugation tests. Overall, this study provides important theoretical reference and methodological support for the practical engineering applications of determining SWCC through centrifugation tests, including seepage analysis of earth-rock dams, evaluation of slope seepage failure, and evaluation of soil water retention capacity.