This paper presents an analysis and execution measures for protection of deep excavation pit in the city centre of Skopje of administrative building with three underground floors. The 1155 m~2 pit borders with two frequent streets, adjacent an existing high-rise building and another construction site. The foundation depth is -12.6 m, around 3.5 m under the ground water level, thus the technical solution should offer adequate hydraulic and equilibrium stability of the excavation pit. A detailed site investigation had detected sandy gravel until -32 m which continues as well compacted marl. Together a combination between soldier pile retaining wall with anchors and jet-grouting elements has been employed to form a hydraulic barrier, seal completely the pit from direct inflow of ground water into the pit. Moreover the jet-grouting will have certain effects on stability through the soil improvement of the local material. A double fluid jet-grouting has been chosen as most effective because a larger eroding diameter was needed. The calculation has been performed using the finite element method while the jet-grouting parameters were defined according EN 12716 and later confirmed with trail investigations. In a period of 2 months 1344 jet-grouting columns with total length of 4893 m had been successfully executed followed by construction of the underground structure.
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