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The W learned about the study carried out by reinsurance experts from the Hidroituango hydroelectric plant, which exposes the reasons why the diversion tunnel collapsed. Thus, the document tells what happened to the design, supervision and construction of this mega-project.
The root cause study conducted by a panel of experts for the reinsurance companies of the Hidroituango hydroelectric contract reveals that the reason behind the collapse of the diversion tunnel was related to unresolved issues of design, supervision and construction in that area of the project, which made this part particularly vulnerable to the hydraulic conditions that occurred in April 2018.
According to the conclusions presented by the researchers, the contractors would have failed to comply with the technical specifications of the contract, they would not have designed and redesigned the project when planning the diversion tunnel that ended up collapsing, and the technical specifications of the work were not followed up properly.
Likewise, it indicates to the controller as responsible for not having made the due evaluation of the technical specifications of the work.
Going into detail, the report signed by academics Christopher Snee, Luis Guilherme de Mello, Bernard Murphy and Rafael Prieto indicates that the diversion tunnel design had weakened in the case of the Auxiliary Gallery, a fact that would have taken away the robustness of the construction.
According to experts, 25% fewer rock bolts or bolts were put into the tunnel section that was weakened. To this they add that the design of the support for the floors was inferior to that of the left and right tunnels, while the shotcrete reinforcement had less resistance than that used in the other two tunnels.
Also within the conclusions of the root cause report they point out that a concrete floor was not made to avoid the erosion of the rock in the tunnel of the Auxiliary Deviation Gallery, which was the one that ended up giving the plugging.
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The experts indicate that although the exact same designs of the initial tunnels were used for the construction of the diversion tunnel, the former were strengthened before and during its construction, whereas this was not the case with the diversion gallery. The research that the designs were deteriorated even during the construction of the tunnel that collapsed.
The report details other design errors; however, there are also several flaws in the construction process that could be attributed to the person in charge of the work.
Experts say that although the contract indicated maximum limits in the excavation, the builder excavated much beyond the authorized ones. They add that in the places where over-excavation was detected, the contractor had to fill with concrete and steel, which was not done.
Regarding the construction part, the reinsurer’s researchers conclude that by changing the type of screws for the diversion tunnel support, the intention was to speed up the construction process, but what was achieved was weaken the support of said tunnel. Likewise, because it was going faster, the support of the shear zone was not installed properly to guarantee the support of the construction.
It is striking that in the same report it is evident that both the builder and the controller knew where the design was not being respected, where the tunnel did not have the expected shape and where the tunnel had collapsed during its construction. This information was also discussed in various meetings recorded in the reinsurer’s document.
