APPLICATIONS / EXAMPLES

Large concrete subway tunnel in Prague

An extension of the subway system in Prague, Czech Republic, crosses the River Vltava. A couple of large concrete tunnels, which are curved in plan as well as in elevation, were cast in the dry dock excavated in the bank of the river. After casting the first tube, it was launched into the trench excavated in the river bed. Each tunnel was cast in segments 12 m long. The total number of 14 segments formed a large tube 168 m long. The outside width of the cross-section was 6.48 m and the height was 6.48 m too. The thickness of the walls and the top and the bottom slabs was about 0.7 m.

During the launching the tube was suspended in one third of the length from its front on the pontoon and at the back end the tube was supported by the hydraulic telescopic sliding shoes. During the launching the tube was subjected to two actions:

• the self weight
• the bouyancy of the water.

Both these actions exhibit a statistical scatter due to the difference in dimensions and in the density of concrete. The actual load is a difference of the two actions and therefore it is extremely sensitive to the variability of them - therefore the balancing forces were applied. There was a danger that imperfections might result in an out-of-control situation.

A statistical feasibility study was, therefore, needed. The imperfections of the individual segments were modelled as random variables - the total number of variables used in the study was 221. The statistical simulation of this technological process aimed at the decision-making process before launching and thus assessing the reliability of the entire project.

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