Experimental Investigation of the Effect of Strip Footing on Shear Band Development and Lateral Pressure Distribution in Helical Soil-Nailed Walls

A series of reduced-scale model tests was conducted on helical soil-nailed walls (HSNWs) under vertical surface loading to evaluate the effect of length, pattern, and inclination of nails on lateral pressure distribution in this innovative retaining structure. The particle image velocimetry (PIV) technique was also used to trace shear bands and identify the failure mechanism. PIV results showed that increasing the nail length, as well as using a square pattern and a 15 degrees angle to install the nails, could be three effective ways to reduce the penetration depth of the slip surface and, consequently, to limit wedge failure dimensions. A linear relationship formed between the lateral pressure induced on the wall facing and the footing pressure at q < q(u). This relationship showed that a greater portion of the footing pressure was converted to lateral pressure using longer nails and installing them in a square pattern and at an angle of 15 degrees. Considering the inverse relationship between lateral pressure behind the facing and wall displacement in HSNWs under vertical surface loading, it was concluded that both pressure and displacement criteria should be considered simultaneously to optimally select the arrangement, pattern, and inclination of helical nails.