Investigation of the Contribution of First Row Rock Anchors to the Retaining System by Variation of Anchor Bond Length

Abstract

In deep foundation excavations, inclined, prestressed soil/rock anchors are commonly used as lateral support elements. During the construction of multi-row anchored excavation systems, sometimes it may not be possible to manufacture anchors in the first row. This situation is often encountered in the production of rock anchors. The presence of discontinuities, karstic voids, and/or historical water channels in the rock environment where these anchors will be manufactured, hinders the injection of the anchor bond length. Additionally, the presence of hard rock units or igneous intrusions in the rock environment prevents the anchor hole from being drilled to the desired length. The application of anchors that could not be drilled to the desired length or those that could not achieve the desired quality of bond zone injection is canceled and usually left as an empty hole. In this study, the usability of canceled rock anchors in the first row, as at least anchors with a short bond length has been investigated. A rock anchor designed to support a 5.0-meter excavation pit to be created in a weathered rock environment, with a prestressing load of 500 kN and a bond length of 6.0 meters, was analyzed using Plaxis 3D software for situations with shorter bond lengths. Accordingly, the function of the related rock anchor can also be fulfilled by an anchor with a bond length of 4.0 meters. When the bond length is 4.0 meters, the entire anchor bond length operates at full efficiency. In anchors with bond lengths smaller than 4.0 meters, the prestressing load of 500 kN causes pull-out failure. However, for example, an anchor with a bond length of 2.0 meters continued to contribute to the overall stability of the retaining system under the effect of a prestressing load of 250 kN.