For the realization of a power plant nearby the city of Aracaju in Brazil, Mammoet Heavy Lifting has been commissioned at the end of 2017 to transport a number of heavy components from a roll-on-roll off facility along the Rio Sergipe river. The assignment was to transport all components a few kilometers inland, using 26 SPMT transports.
Part of the transport route is on a narrow, unpaved road that runs through a mangrove forest. Mangrove is characterized by very weak soils that alternately are under water or dry (under the influence of the tide). The weights of the parts to be transported varied from approximately 150 tons to a maximum of approximately 500 ton. The parts are not only heavy, but also very valuable. Timely presence at the construction site is also important to avoid compromising the project planning.
In order to avoid all risks during transport, Mammoet has requested local geotechnical advice for the approach to be followed. This led to a design in which the original ground under the dirt road would be partly excavated and backfilled with sand. On the sand backfill a base course of heavy quarry stone was foreseen. (Photo 1)
In order to demonstrate the functioning of the principle, a test strip has been constructed on the basis of the geotechnical advice over a length of approximately 50 m. Unfortunately, practice proved more difficult than theory. The sand supplement was instable and the base course settled excessively before any load was present.
Mammoet therefore asked Geobest to evaluate the locally devised solution and, if possible, improve it, so that the transport could take pace safely and in a timely manner. An important precondition was the demand to bring back the terrain back to its original state after the transports have been completed.
Geobest has assessed the plans and proposed to leave the local solution largely intact, but to improve the stability of the construction by adding heavy geogrids between the sand backfill and the base course. Based on calculations with the finite element program Plaxis 2D, it has been proved that the stability of the construction against subsidence by the chosen solution could be increased significantly. Geogrids proved to be available locally and are easy to remove afterwards. (Photo 2)
At first it was found that the soil improvement in the initial test strip was instable, because the sand used was very fine and poorly mechanically compacted. This is why Geobest recommended to use coarser sand, which was available relatively close to the site for the soil improvement.
In view of the large financial and technical risks it was necessary to give the project manager of the client a solid explanation on site. The consultant therefore flew to Brazil at short notice. After a short work visit on the site, a technical meeting was organized. The results of the Plaxis 2D calculations were explained to the technical advisor of the client and in consultation with the project team of Mammoet some additional load cases and worst case scenarios were calculated during the meeting.
After convincing the client, Geobest prepared a method statement for the practical execution of the work with the Mammoet project team. Finally, a plan has been drawn up for a test transport, of course, with the necessary deformation measurements. Once back in NL, Geobest remained remotely involved during the execution process of the road construction. After the completion of the route, the test transport was carried out, with the deformations being limited to only a few centimeters. After this, the route was released and all 26 transports were carried out safely and on time (see drone recording).
The entire transport operation has now been completed. The required maintenance on the transport route was minimal. The narrow dirt road has been restored to its original state and is once again the domain of monkeys, anacondas, birds and insects as if nothing ever happened.