Study on the characteristics and influence factors of pull-out resistance of vetiver root in expansive soil

Studying the pullout characteristics of roots can help to gain a deeper understanding of the interaction mechanism between plants and soil, and provide theoretical support and practical guidance for engineering applications. This paper aims to investigate the pulling characteristics of the root–soil interface in expansive soil reinforced by vetiver roots. For this purpose, the study focuses on exploring the correlation between the pullout force (PF) required to extract the roots and the pullout displacement caused by the extraction. The research also examines how the geometry of the roots affects the pulling characteristics of the root–soil using a pullout test. It is found that with increasing root diameter, root length segment (RLS), root volume, and root surface area (RSA), the maximum PF increases. The highest correlation coefficient was found between RSA and maximum PF, which explained 81.4% of the variation in maximum PF. Then, the functional relationship between RLS and PF is established. Using RSA to predict the maximum PF of vetiver root is relatively reasonable. The assessment of PF must consider RSA indicators. The increase in RSA due to a high number of roots results in the improvement of the PF of vetiver root. These findings could assist in enhancing the strength of expansive soils.