A laboratory device to test the pull-out behavior of soil nails

摘要

Soil nailing is an in situ soil reinforcing technique adopted for stabilizing existing slopes in Hong Kong and in many other countries and regions. For the design of a soil nail system, pull-out capacity of a soil nail is an important design parameter. Field pull-out tests are then carried out to verify the pull-out resistance assumed at the design stage. However, the pull-out capacity of a soil nail in the field is influenced by a number of factors, such as variation in the soil properties, variation in the installation procedures, types of soil nail, and stress levels. Thus, field testing has a number of limitations. To overcome the limitations, a new laboratory pull-out testing apparatus was developed to investigate the interface shear strength behavior of the soil nails and surrounding soil. A numerical analysis was carried out to assess the initial stress conditions in the laboratory pull-out test box. A series of laboratory pull-out tests was performed with a cement grouted nail in a Completely Decomposed Granite (CDG) soil. It is aimed at studying the influence of overburden pressure, soil degree of saturation, and surface roughness of soil nail on the interface shear strength. The results indicate that the curves for pull-out tests exhibit a significant peak and post-peak shear strength behavior. And the interface shear strength between the nail and soil is shown to be dependent on the normal stress, the soil degree of saturation, and the surface roughness of the nail. A correlation of the interface shear strength with major influencing factors is then derived for practice design applications. The findings in this study may be a useful reference for geotechnical engineering in soil nailing design and constructions and for better understanding of the soil nail pull-out performance in the soil.