Physical Modeling of the Helical Anchor Walls’ Behavior Using Particle Image Velocity

Abstract

Helical anchors are construction elements with a wide range of applications in geotechnical engineering such as excavation shoring, retaining wall construction, underpinning, seal wall construction, and foundation construction and reinforcement. In the present work, a laboratory model of a helical anchor wall is presented and evaluated. For this purpose, four types of anchors at three back slopes are designed in a sand soil and the effect of helical configuration (in terms of its diameter and number of helices) and back slope on wall crest displacement is investigated. Considering the laboratory scale of the designed model, the results obtained using the helical anchor were compared with laboratory results of soil nailing wall by applying the particle image velocimetry analyses. The results show that an increase in the back slope shows better the effect of the type of helical anchor and leads to a more efficient wall stabilization. As a result, in the case of surcharges, using a larger number of helical anchors and a higher number of helices would lead to better performance. In a wall with a 20° back slope, for example, an increase in the number of helices from 1 to 2 resulted in a 43% reduction in the displacement of wall crest. Besides, by changing the number of helices from 1 to 3, the displacement of wall crest was decreased by 62%. Since all anchors require a slight displacement rate to activate, in case the displacement required to activate the anchors exceeds the permissible displacement of the wall crest, it is recommended using a posttension helical anchor. Finally, it was found that the displacement of the wall’s crest in using the helical anchor method was much less than that of the nailed wall and the slip surface created in the helical anchor wall was parabolic.