On 7 September 2021, Zetas’s team was awarded a contract by the Abu Dhabi municipal authority to improve the soil beneath the existing roads around Mleih school, in Sector 6 of Shakhbout City.
Ground improvement methodology has been proposed against potential cavities or fracture zones in rock formation, and excessive settlement most likely due to desalination of existing salt formation due to groundwater movement and pressure applied to rock.
Due to the short lead time and the limited budget of Abu Dhabi Municipality – ADM, (in maximum four months duration for tendering and execution of work), The initial proposal, to build reinforced piles connected to the RCC slab under the road structure, has not been evaluated as feasible by ADM.
This is the revised technical proposal, involving cavity grouting and rigid columns without reinforcement, eventually won everyone’s support:
Thanks to their expertise in geotechnics and special foundations, Zetas’s team imagined and implemented a rapid solution, effective in the long term and significant savings on the project’s overall budget.
The project involved constructing 3,908 cavity grouting to a depth of 5m and 869 injection points to a depth of 20m.
The CFA method was selected for drilling a rigid inclusion column without reinforcement. During drilling with CFA method, Zetas’s team is observing / checking the existence of salt formation. If the salt formation is encountered (e.g. more than 10 to 20 cm thickness), it is excavated and replaced with suitable backfill material.
The soil improvement process included: drilling 3908 columns 0.4m in diameter according to a rectangular grid spacing of 1.5m in both directions, as well as a road surface design incorporating a load-transfer platform (two layers of StrataGrid Hyten geogrids perpendicular to one another) with a geotextile membrane separating the layer of soil or road backfill, which were proposed in order to minimise settlement and achieve a strong and durable base and sub-base.
The columns were modelled as a soil element to distribute and transfer surcharge loads all along its width (0,4 m) to soil and rock formations.
The main challenge of this project is the deadline. Indeed, 4 months to carry out the work (including the call for tenders’ phase) is very short! Considering the methodology has been implemented , the coordination between the road main contractor and Zetas’s team as ground improvement subcontractor is becoming very crucial to achieve the planned completion date.
Overall progress of the works is in line with initial program and with additional 250 m2 area.
The completion date planned for the entire scope of the works is end of December 2021.
Thanks to this project, with this specific combined application, which brings significant savings in short time, Zetas’s team are ready for new similars road repair projects.