Our team was involved in a rescue project in the Britalia neighborhood of Bogota, a historically disadvantaged area. This project took place in the same challenging ground conditions as the previously described Tunjuelo project. However, this task was even more difficult as our objective was to rescue a stuck guided boring machine (GBM), which had become lodged in the ground.
Another construction team had initially encountered issues at the beginning of the project, during their first drive, at the 20 meter mark (total drive was 74 meters). They were using a Bohrtec BM500 machine. The conditions were similar to that of the Tunjuelo project in that the mixture of groundwater and sand presented the potential for liquefaction.
The problem for the initial construction team arose when the first guided boring machine used on the project - the Bohrtec machine - got stuck at 20 meters. Another construction team built a shaft over the machine to extract the head of the Bohrtec and they decided to continue the drive from the 20 meter mark with an Akkerman guided boring machine. At the 34 meter mark, the Akkerman machine also got stuck in the liquefied sandy conditions. That’s when Petra was called in to rescue the second stuck machine.
To understand why Petra could proceed with this product when other machines and teams couldn’t, you have to understand why these machines got stuck in the first place. When using a GBM (which has a rotating head like a conventional large TBM), your rotating head creates a void in the front in water-logged sandy conditions. The void causes the machine to try to force its way upward. Then the augers that you use in front of the head try to force the machine downward. These conflicting forces increase the pushing force and eventually causes the machine to get stuck. In these scenarios, the more you try to increase the rotation of the cutter, the worse the problem gets and eventually the machine stops advancing entirely.
To remedy this, when Petra came in to rescue the Akkerman machine, we employed our Petra Platform in ADB mode to ram in a larger casing that swallowed the existing concrete pipes, slightly bigger than the concrete pipes the Akkerman had been installing.
We successfully reached the head, recovered the pipes and the head, and continued until we reached the endpoint. We used our ADB mode to more efficiently jack in a metal casing that was the entire length of the crossing, over the stuck machine. After we completed this, we pulled out the internal concrete pipes and the stuck machine from the entry shaft. Because we don’t have a rotating head on the ADB module, we didn’t create voids in the wet, flowing sand.
