Study on the Interface Properties of Fine-Grained Gravelly Soil Based on Pull-Out Test

In the field of roadbed engineering, reinforced gravelly soil fill materials that are subjected to long-term upper load actions are prone to phenomena such as fine grain intrusion, leading to the deterioration of the mechanical properties at the reinforcement-soil interface. In order to study the influence mechanism of fine grain content on the reinforcement-soil interface, this paper considers factors such as normal stress, pullout rate, and relative compactness. Pullout tests were conducted on gravelly soil fill materials with different fine grain contents to discuss the coupled effects of multiple factors on the strength and volume change characteristics of the reinforcement-soil interface. The research findings indicate: (1) Under different pulling rates, an increase in fine particle content leads to a shift in the pulling resistance curve from hardening to softening, with a gradual enhancement in interface shear contraction. There is a threshold between 0-10% for fine particle content where the impact of pulling rate on peak pulling resistance can be neglected. (2) The contact state of particles within the specimen of medium compactness is uneven, and the pull-out resistance curve shows a stepwise decline at 0% fine particle content. Under the same fine particle content, the peak value of pull-out resistance is positively correlated with relative compactness. The shear shrinkage at the interface due to the influence of expansion force is most pronounced when the compactness is low and the fine particle content is high. (3) When the normal stress is the same, an increase in fine particle content leads to a reduction in the displacement and magnitude of peak pullout resistance, exacerbates strain softening, and restricts shear dilation. Fine particles can decrease the apparent cohesion and increase the internal friction angle, with the peak shear stress being significantly influenced by the internal friction angle. The comprehensive friction factor ratio has a negative correlation with both the normal stress and the content of fine particles. (4) Analyze the error interval between the actual value and empirical value of shear stress under different conditions, and propose a proportional expansion coefficient P=1.05 for use in the calculation of the empirical value formula.