Influence of grouting pressure and overburden stress on the interface resistance of a soil nail

Grouted soil nails are widely used in slope stabilization. The influence of both grouting pressure and overburden stress on the soil-nail pullout interface shear resistance is still not well understood due to the complex of soil-grout interactions. A series of laboratory soil-nail pullout tests have been carried out on a completely decomposed granite soil in nearly saturated condition under a combination of different grouting pressures and overburden stresses. The pullout tests simulate the real construction process of a soil nail, including establishment of initial soil stresses in a soil slope, drilling a hole with stress release, grouting, and soil-nail pullout when the slope is sliding. The pullout box is well instrumented. Test data are collected automatically by a data logger. Typical test results are presented, explained, and discussed in this paper. The soil-nail interface shear resistance data from all tests are analyzed and interpreted. The study shows that the grouting pressure and overburden stress have interactional influence on the soil-nail pullout resistance. Based on the test results, a new empirical liner equation with two grouting pressure dependent parameters is proposed for calculation of soil-nail pullout resistance considering both grouting pressure and overburden stress. New understandings and findings from the study are presented.