Arching effects behind a soldier pile wall

Abstract

A wall consisting of anchored steel piles with horizontal timber laggings was selected to support a 16 m deep excavation with a length of more than three kilometres near Cologne in Germany. Vertical holes were bored on the wall line, at 4 m centres, and steel piles were placed within these holes. Good contact between the piles and the surrounding soil was ensured by concreting the remaining space in the holes. In this way the earth pressure behind the wall was transferred to the piles through horizontal arching, so relieving the timber laggings. As a result, lighter timber laggings could be used and the economy of the wall construction could be increased. In situ tests as well as non-linear 3D finite element (FE) analyses were carried out. Horizontal arching was promoted by means of flexible horizontal lagging timbers and solid contact between the piles and the surrounding soil. Vertical arching was induced by high pre-stress forces in the upper ground anchors. FE analyses were based on both the elasto-plastic Mohr–Coulomb model and a more advanced hardening-soil model.