Tramway stabilization and re-levelling in the center of Tallinn

THE PROBLEM

The waterway accident in the center of Tallinn, at the intersection of Mere puiestee and Ahtri Street, resulted in stopping tram traffic. A 200 mm diameter water pipe broke. Asphalt next to the tramway subsided at the accident site and the sinkhole opened. As the load-bearing structural layers under the tramway were washed out, tram traffic was stopped. One of the trams that derailed from its path was also affected. According to City Transport Company, the water accident was very extensive, resulting waterflow approximately 800 cubic meters per hour.

WORK PROCESS WITH URETEK TECHNOLOGY

This was a rather rare and unique case, in which the time factor played a particularly important role. The intersection, where the work needed to be performed, is one of the busiest in the city. The water accident caused stoppage of several tramway lines.
As a first phase, the void was filled with as much sand as possible. In this operation, the filling process was made from the side and the sand was pressed into the voids under the concrete tramway slabs.

In the second phase, URETEK filled the cavities under the tramway slabs with an expandable geopolymer. The injections were started from a depth of 3 meters to ensure the largest possible reinforcement of the soil and to press the sand fill against the tramway structure.

As the third phase, after filling the gaps, URETEK started lifting the tramway slabs and re-levelling them to their original position. This work was performed using a tram specially ordered from the fleet, which was used as a weight in the injection area. The same tram was used several times to check for possible slab descents. The final result – accuracy of the work was measured up to 1 mm, taking into account the initial height and the final height after the job.

THE RESULT

At 8:00 in the morning the accident was discovered.
At 9:00 URETEK made a call to the appropriate authorities about the problem.
At 10:30 URETEK visited the site and discussed possible solutions to the problem.

The appropriate paperwork and the preparation time took from 12:00 to 21:00. The execution of the works started from 00:00.
During the works, the initial position of the tramway was restored and, in agreement with the customer, it was decided to increase it by another 2 mm in order to prevent any subsidence due to soil compaction.