Net load–displacement estimation in soil-nail pullout tests

Soil-nails are used to stabilise a soil mass by exploiting the resistance generated by the skin friction between the ground and grout and the tensile stiffness of the reinforcing material. A load–displacement curve is obtained from in situ pullout load tests performed by considering the elastic shear modulus and ultimate skin friction capacity between the soil and grout. This study determines the shear behaviour between the soils and grout analytically, especially the soil-dilation effect during shearing that is one of the main factors affecting the ultimate skin friction, even though this estimation is rather cumbersome. Many studies assume a full bond between the grout and the steel reinforcing bar, thus neglecting their relative displacement. In this study, the net load–displacement between the ground and grout is obtained by subtracting the nail elongation from the load–displacement of the pullout tests when estimating the shear displacement. Numerous field pullout tests are performed in this study under various ground conditions and through various construction methods. The dilatancy angles are estimated dependent on the soil type by comparing the net load–displacement curve obtained in the field with that obtained theoretically.