FCC headed the execution of the Riyadh Metro project and was in charge of the construction of three lines (4, 5 y 6). During the excavation of line 5, two TBMs were used, producing more than 2 million tonnes of excavated material that had to be managed. These materials were in slurry form, and therefore needed pre-treatment to transform them into mud before removal from the tunnel; However, the city did not have the necessary sites to carry out this treatment, which made the management of these materials a challenge. The only option available for managing these materials was their disposal in solid waste landfills, even if this meant significantly increasing the volume of waste sent to the landfill and significantly decreasing its capacity.

The must sustainable option was to treat the excavated material as reusable soil to reduce the volume of waste and maximise the level of reuse as much as possible. Therefore it was suggested that the material extracted from the tunnel be reused in municipal landfills as a daily or final covering layer. We collaborated with the Riyadh council and agreed to take the waste to the Al-Sulay landfill where it would be used as an earth covering for the landfill. The process was controlled using a system of tickets managed by the council and heads of the trucks and tunnel boring equipment.

The benefits from the adopted measures were twofold: On the one hand 100% of materials excavated by TBMs were reused, implying a significant reduction in management costs and there was also a significant improvement in waste management. The reuse of the material excavated by the TBM improved the covering on landfills, preventing water infiltration and moisture. Furthermore blocking holes and pores in the top covering meant that the level of gas leakages was reduce, therefore minimising the amount of leachate and odours and increasing the level of recovered gas.