Effect of Variation of In Situ Moisture Content on Pullout Capacity of Grouted Soil Nail

Soil nailing has traditionally been used as a method to retain soil excavation and to stabilise soil slopes. The effectiveness of this method depends on the pullout resistance of the nail, amongst other factors. There have been instances when the shear resistance between the soil and the nail has deteriorated when the soil volume reduces or when the soil shrinks with the decrease in moisture content. This can happen during the curing period of the cement used in the grouted nails. In the present study, a number of laboratory model tests were conducted in cemented grouted nails installed within silty soils. The variation of pullout resistance with curing period of the cement grout was determined. Spatial variation of the moisture content with depth and distance away from the nail was determined after each pullout test. To support the findings, direct shear tests were performed between the cement grout and the soil at the same moisture content at which pullout tests were conducted. The results indicate a reverse behaviour of the interface friction angle due to the change in moisture content.