The site is located in a quite densely populated business district of Istanbul. For the construction of 23 m deep excavations for 7 basements, a shoring system was needed. Next to the project area a connection tunnel and an entrance shaft (a municipal investment) were under construction which complicated anchoring at those zones.

Our company provided whole scale services including ground investigations, deep excavation design, analysis of interaction with adjacent structures, construction supervision and geotechnical instrumentation.

Due to the geometrical interaction between the excavation and the ongoing construction of the adjacent tunnel and shaft, analysis in a plane-strain model was not possible and a 3D FEM analysis was necessary.

The shoring system was designed as a piled-prestressed ground anchored system. At the interaction area where ground anchors couldn’t be installed, steel struts were used. The impact of the deep excavation on the tunnel and shaft structures was analysed with a 3D FEM model. The results of the impact on these structures obtained from the 3D FEM model were significantly more reasonable than those obtained from 2D FEM models and a cost-efficient design could be adapted for the steel strut supports. Design results/Performance comparison was continuously done throughout the construction phase using sophisticated geotechnical instrumentations (inclinometers, strain-gauges, load cells, optical surveys). The instrumented results were found to be in line with the results of the 3D analysis.

As a result of a new generation design method and an in-situ monitoring scheme, a cost-efficient design could be made. In addition, by convincing the municipality, delays in construction were prevented for the client.  Also, the municipality benefited by securing their important infrastructure investment. The results were presented with a scientific article in the “18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013” and the benefits achieved by means of a new generation design philosophy was presented to the international engineering society.

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