The influence of grouting pressure on the pullout resistance of soil nails in compacted completely decomposed granite fill

The interface shear strength between a soil nail and the surrounding soil is required in 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. Some initial results from field pullout tests on soil nails grouted under pressure have indicated that the grouting pressure contributes to the pullout resistance. Pressure grouting is a cost-effective method for increasing the soil nail pullout resistance, thus improving the performance of the nailed structure. Studies on the soil nail failure mechanisms and quantitative data from tests investigating how grouting pressure influences the pullout resistance are, however, very limited. First, this paper introduces a laboratory soil nail pullout box with full instrumentation and a special pressure grouting device and its set-up. Second, the paper describes the test procedures and a programme for studying the influence of pressure grouting. The paper presents representative test results. The influence of the grouting pressure together with overburden soil pressure on the pullout resistance is examined. From the test results, relationships between pullout resistance and grouting pressure are obtained and discussed.