Building a new terminal on a narrow piece of land surrounded by water is a challenge for all parties involved in such project. In particular, when it comes to the management of cut and fill material with no stockpiling area available out of the project boundaries.
During the construction of COMPAS Bulk and Coal terminal in Buenaventura Port, Colombia, the design already considered to use the cut material above the yard final elevation to fill in the lowest parts of the Aguadulce peninsula. The cut material is mostly clay and after lime-stabilization process, it meets the physical properties required for fill. However, all excavated material was not suitable for backfilling purpose. The superficial silty clay with its organic content, high water ratio and plasticity index was considered unsuitable. Some bay areas were already designated as deposit inside the boundary of the terminal. On paper, the balance was achieved between fill volume, cut volume of suitable and non-suitable material.
But like all projects, the events did not exactly occur as planned. During the excavation works, the team had to deal with a significative increase in proportion of unsuitable excavated material. The area for stockpiling could not contain any more material.
The team looked for two ways to find solution.
The first one was to search for a suitable stabilization process to make that material compatible with backfilling. Different dosages of lime were tested on site. We even considered cement mixing or polymer additives. But the daily heavy rain that falls in the area made it impossible to reach adequate results with acceptable costs and production rate.
The second one was to change the design of the stockpiling area and their retention structures to come as close as possible to the statutory boundaries of the terminal to fit the surplus volume.
Some bulkheads were changed into sheetpile wall with tie-rods and anchor wall, others into geotextile megabags dikes filled with the same cut material. Inside the deposit area, due to the high seismicity in the region, it was also required to use ground improvement techniques to guarantee the stability of the bulkhead. Rigid inclusions or consolidation (wick drains with surcharge) were the two techniques employed.
This alternative was finally chosen by all parties because it was in line with the development plan of the terminal to expand the yard surface in future. Indeed, ground improvement was done over the whole stockpiling area to reach a bearing capacity of 2 ton/m2 or above at the final yard level.
This second alternative is the focus of the paper. It’s a good reference for a win-win project where design and site constraints are evolving in line with owner’s needs. For port planners, it is also pointing out the importance of leaving buffer zones in the terminal layouts and not to underestimate the soil investigation campaign for a more accurate quantitative and qualitative assessment.