Influence of Critical Parameters on the Peak Pullout Resistance of Soil Nails Under Different Testing Conditions

This paper presents a comprehensive analysis of the correlation between influencing parameters and peak pullout resistance (PPR) of soil nails installed in typical completely decomposed granite (CDG) or sand. A total of eight soil nail pullout tests were conducted in a field to examine the influence of overburden pressure (OP) and grouting pressure (GP) on the PPR of soil nails. Comparative analysis indicates PPR values of soil nails pulled out in soils with low degrees of saturation (30%) are almost twice of that in almost fully saturated soils. Apparent coefficient of friction (ACF) increases linearly as the increase of GP, but decreases linearly as the increase of OP when GP is constant in both laboratory and field tests. Extensive studies also show that the magnitude of normalized ACF is more sensitive to OP compared with GP and degree of saturation (S_r). Diameter increase in percentage of soil nails pulled out from field are almost twice of the soil nail diameters in laboratory tests, indicating that due to complex geological condition in field (such as possible high void ratio of field soils), failure surface of soil nails presents substantial shift into surrounding soils.