Test Study of Pullout Resistance of Soil Nails in Compacted Completely Decomposed Granite Fill

Abstract

The interface shear strength between a soil nail and the surrounding soil is required for the design analysis and safety assessment of a soil nailed structure, such as a slope, retaining wall or excavation. It has been found that a number of factors may influence the interface shear strength, such as the normal stress, soil properties, soil nail surface roughness, degree of saturation, and grouting pressure. Firstly, this paper introduces a laboratory soil nail pullout box with full instrumentation and special devices for controlling the degree of water saturation, pressure grouting, and the setup of this box. Secondly, the paper describes the test procedures and a programme for studying the influence of over-burden pressure, degree of water saturation, pressure grouting. The paper presents representative test results. The influences of over-burden pressure, degree of water saturation, grouting pressure on the pullout resistance of soil nails are examined and discussed. From the test results, relationships between pullout resistance, over-burden pressure, degree of water saturation, and grouting pressure are obtained and discussed. In general, the over-burden pressure has little influence on the pullout resistance, the increase of degree of water saturation will reduce the pullout resistance. Grouting pressure will increases the pullout resistance. The increase may be more evident when the over-burden pressure is larger due to confinement. Pressure grouting is a cost effective method for increasing the soil nail pullout resistance, thus, improving the performance of the nailed structure.