Performance evaluation of a 21m deep excavation stabilised by combined soil nails and anchors – A case study

The design and construction of deep basement excavations requires careful analysis with respect to the staging and support of the excavation works. In urban environments, these issues are even more critical due to the potential for settlement of adjacent structures. Hence an understanding of the overall stability and ground deformation becomes paramount. In this paper, case study of a 21 m deep excavation adjacent to a 4 story residential building in soil alluviums in Tehran is presented. A combination of high pressure grouted soil nails and anchors was adopted to provide lateral support. Finite element and limit equilibrium analyses were conducted to predict the performance of this deep excavation and to evaluate the impact of the excavation on the existing adjacent structure. Displacements and anchor loads were monitored during various stages of the construction. Monitoring results and numerical predictions of displacements and reinforcement forces correlate well. The level of correlation between the parameters predicted in design and the measured results from monitoring lends credibility to the design methods adopted and should give confidence in their use to achieve safe design and construction of future excavations.