The ongoing project for the deepening of the canals of the Varna Lake could have fatal consequences for the safety of the Asparuh Bridge in Varna.
This is clear from a video interview published today by the Anti-Corruption Fund (ACF) with professor and lecturer in geotechnics Dr. Eng. Dobrin Denev, who in the 1970s assessed and developed a solution for strengthening the bridge. AKF spoke with Dobrin Denev as part of its video series “Swamp Stories from Varna Lake”.
Prof. Dobrin Denev is an expert in geotechnical engineering and former Rector of the University of Architecture, Civil Engineering and Geodesy between 2008 and 2011. In the 1970s prof. Denev was one of the experts who found a constructive solution to the safety problems in the construction of the Asparuh Bridge. The problem then was the compromised performance of the bridge’s strengthening columns, the so-called “piles”:
“What is mandatory, one of the laws I would say of the performance of this type of piles, is that the concreting be continuous. And there have been interruptions. Concerned professionals say, ‘Let’s see what’s inside the pile.’ They do little borings inside and they go through concrete… and all of a sudden it’s just sand… all of a sudden it’s mud, silt. More than 50% of the piles are compromised. These protocols are right here, “Weak, wet concrete continues to come out of the 18-foot-deep borehole.” Six months after concreting, it’s weak – it will never set. That is, in every respect things are worrying.”
To compensate for the shortcomings of the compromised original columns, Prof. Deneuve suggests pouring additional reinforcing concrete columns.
In February 2022, Prof. Deneuve carried out a new examination of the bridge, during which it became clear that some of the planned reinforcing pile columns had never been installed, however.
“The Execution Report shows that such reinforcements were made to one of the piers and six piles were put in addition. However, it appeared one of the two pillars had no such extensions. Probably the slab was already executed on one pier only.”
This is particularly important information against the backdrop of the canal widening project currently underway on Varna Lake, which passes directly under the central span of the Asparuh Bridge. According to prof. The project poses new safety risks:
“When a ship passes, it raises a wave that crashes into the banks, literally speaking, and when the ship passes, there is a movement in the opposite direction. And the quicksand on top, which is about 10 metres thick, will go into the channel. And all this can lead to really extremely undesirable consequences. What are they? The pilots to be stripped – their first 5-10 metres, and they are to one degree or another questionable as to performance, to say the least. One small earthquake is enough. It’s enough for heavy vehicles up on the bridge to stop abruptly. The picture, so to speak, is hidden. Everything is in the ground. And like information, it’s also been hidden for years – 50 years since then.”
The Varna Lake Deepening Project calls for new lining of the slopes where the abutments are located. The problem is that before the new lining can be installed, the old lining will be removed and the shore will be exposed.
“This is the dangerous point. The implementation technology may prove to be counterproductive, i.e. the stability of the bridge may be challenged. And I am deeply convinced that all this is repairable. Our expertise has a recommendation on how to get out of this situation. With sheet piling – it is implemented in a matter of days. They will be a kind of barrier. We have protection on the bridge abutments. What we fear most may not happen,” concludes Prof. Denev.