Effect of the anchors' free length that made of tubular screw rods on the forces distribution in pile-anchor retaining structures on highways

Pile-supported retaining structures are widely used to protect road sections from landslide processes. The article describes the design and calculation peculiarities of pile-supported retaining structures reinforced with a drill and inject anchors from tubular screw rods. The authors considered two options for this type of anchors setup: without free length and with a pre-set free length. In the software geotechnical complex Plaxis, on the finite element method basis, mathematical modeling and calculation of a pile-supported anchor retaining structure with different free anchors lengths from tubular screw rods for various soils types have been performed. Numerical relationships have been obtained between the anchors' free length and the resulting forces in the retaining structure. The performed calculations series of the test scheme showed that with an increase in the free anchors' length in the retaining structure, there is a decrease in the applied load in its load-bearing elements due to the horizontal displacements growth. The article presents the survey results of a real road section, on which a landslide displacement is being prepared, and considers a design solution for a pile-supported anchor retaining structure to ensure its safe operation. Performed a series of calculations for various landslide process development stages in this area showed that the effect of the anchors' free length also largely depends on the state of the adjacent soil mass. Obtained results clearly show that the design of a free length section for anchors made of tubular screw rods makes it possible to design more cost-effective pile-supported anchor holding structures without reducing their reliability.