Experimental Investigation and Constitutive Modeling of Grout–Sand Interface

The shear stress-displacement behavior and shear-strength parameters of the interface between the cement grout nail and surrounding soil are important factors in the design and safety assessment of a soil-nailing system. One of the most commonly used methods to measure the interface shear strength of a soil-grouting system is the direct shear testing method. This study aimed to investigate the behavior of the interface between the cement-grouted materials (soil nails) and sandy soil using direct shear test apparatus, make a comparison between the sand-sand interface and grout-sand interface, and calibrate an interface model to be used in simulations of soil-nailing systems. The effect of the water: cement ratio of the grout and the relative density of the sand on the interface behavior is also investigated. The findings show that, in general, the behavior of interfaces is similar to that of dense sand in terms of strain softening, and their peak and residual friction angles were found to be approximately 8 and 4% higher, respectively. The setting time of the grout and relative density of the sand were not found to affect friction angles significantly, whereas cohesion intercepts were affected by it. Finally, the model calibrated herein was found to have good agreement with experimental data and could be used for soil-nailing simulations. (C) 2019 American Society of Civil Engineers.