Permanent uplift Anchors in Copenhagen Limestone

Abstract

On the former Postal Service Centre parcel in central Copenhagen a new urban area of 200,000 m2 is under construction, which accommodates service and retail trade, as well as apartments for housing. Below ground a parking basement in two levels is established with excavation to 8 m below ground level, corresponding to approximately 8 m below the design ground water level. To resist the uplift forces on the basement approximately 950 vertical ground anchors were needed. Because of the large number of ground anchors an initial test programme has been performed with the goal of minimizing the overall costs and to ensure a robust anchor project. The test programme consisted of 23 investigation tests on vertical ground anchors with varying anchor bond length, where the aim was to obtain failure in the interface between the grout and the limestone. All test anchors were installed with the anchor bond length in the Copenhagen Limestone. This paper describes the geology of the area, the concept for the preliminary anchor design, the test programme, and the results and conclusions. Furthermore, a description of the design and installation of the production anchors. The test programme showed that the anchor bond length could be reduced to (at least) 4 m for resisting a design anchor load of 1250 kN, corresponding to a measured shear resistance more than 70% greater than initially presumed. Based on this the production anchors were installed and tested by suitability and acceptance tests according to DS 1537, and all anchors passed the test.