Maintenance of Monitoring Equipment
In March of 2022, the Terra Monitoring team set out to conduct annual maintenance of the settlement cells and seepage weirs in Eswatini at the well-known Maguga Dam.
A Settlement Cell is a device installed in embarkments, fills and foundation soil to monitor settlement which determines the stability of a structure at an installation point. A settlement cell consists of three components: a tube filled with Ethylene Glycol, inline to a pressure transducer, and a reservoir unit also filled with Ethylene Glycol.
When air enters the fluid in the system, the settlement cells run the risk of having inaccurate readings. Thus, settlement cells require regular maintenance by replacing the existing fluid used in the tubes and reservoirs with fresh deaerated Ethylene Glycol. This mixture not only improves the accuracy of the readouts delivered by the Pressure Transducer, it also prolongs the lifetime of the system. With a large facility such as Maguga dam, which has a capacity of 332 000 000 m³ of water and a wall height of 115 meters, it is imperative that the monitoring systems relay accurate data to determine the condition and the health of the structure.
Upon arrival on site, the team immediately started the maintenance process by replacing the old Ethylene Glycol, which is yellow in colour, with a red variant. This colour system ensures that the technicians can easily identify that the system has been purged of the mixture previously used and that any remaining residue is identified and removed. This will allow the monitoring system to run optimally. To replace the fluid in the system, the team needed to flush out any of the existing liquid with the new mixture. To do this, the storage tank pressure was raised to 200 kPa. The technicians would then introduce the new mixture into the system while using a vacuum to extract the existing fluid. They must then continue with this procedure until the liquid in the system appears bright red as an indication that the residue of the yellow liquid is no longer present. The Terra Monitoring team had to take extreme precautions to avoid that air would enter the system while they replaced the fluid. Should air enter the system, the process to flush the system will have to be restarted. Equipment used during the Purging process included a compressor, Vacuum Storage tanks and a Nold DeAerator™.
The maintenance of the settlement cells was completed successfully and within the required time frame.