Highlands Gate Estate | Dam upstream of culvert | Roadway over culvert | Nov 2012 showing failure | Culvert outlet failure to be rebuilt | Feb 2013 showing failure | June 2013 setting out structure | Gabions and geotextile arrive on site | July 2013 showing progress | August 2013 progress | September 2013 progress | Formwork for concrete capping on layers | September progress | Corner wall to be extended | Preparing for gabions | Gabion packing underway | Laying geotextile for river mattresses, overlaps 300mm | June 2013 river mattress placed | June 2013 mattress progress | September progress | Completed Gabion Structure - October 2013 |
Pro.com Civil and Structural Consultants in Nelspruit were approached by The Highland Gate Golf Estate, near Dullstroom, to assist with the planning and design to replace a failed gabion structure, at the main dam, to protect the spillway. The spillway consists of 9 Armco culverts, forming part of the dam wall. Flood water took the gabion structure at the down steam side away leaving a vertical unprotected gravel face of approximately 4m high. The gabion baskets stayed intact and were unceremoniously dumped about 10m further downstream and partly covered with loose sand and stone. The mesh reinforced concrete topping on the top row of gabion baskets was approximately 100mm thick with a heel of approximately 750mm deep and 350mm wide.
Pro.com did a detailed survey of the area to determine the extent of the project and to plan and design a mass gravity gabion wall to protect the spillway. Pro.com designed a wall with a 6 degree batter, founded on river mattresses to protect the structure from under-scouring and Gabion Guru from Nelspruit was appointed to construct the wall.
Work started on the 4th June 2013 to give Gabion Guru sufficient time to construct the structure in the dry season, under the close supervision of Pro.com Nelspruit.
The removal of the rock from the existing baskets and the breaking of the concrete topping was a major challenge. Gabion Baskets had to be cut open and rock removed by hand. The concrete came to rest at many different angles and positions, which made it very difficult to break on site. Gabion Guru used 2 conveyors to move the rock from the cleaning up area to the construction face and rock breakers supplied by the friendly people from Coastal Tool Hire in Lydenburg were used to break the concrete.
Approximately 300 tons of un-selected rock has been imported from a commercial source in Machadodorp, about 100km away, to replenish the volume of rock recovered from the failed baskets. The last stretch of 15km dirt road from the Belfast to Dullstroom main road has not been maintained for a long time and it claimed many tires and dented many rims. To complicate matters, the estate did not allow the 30 ton delivery trucks on the paved roads in the estate, therefore the rock has been offloaded on a designated area and then transported with 10 ton trucks to the construction site. A treacherous downhill stretch and sharp turns in the road also made it impossible for large vehicles to reach the site.
Pro.com, Gabion Guru and our supplier, Gabion Baskets, proved to be an efficient team with quality workmanship and gabion products manufactured to SANS requirements. The excellent working relationship between Pro.com Consultants, Gabion Guru and the Management of the Estate also contributed to the success of the project.
Kindly contact Mr. Fanie Joubert of Pro Com at 082 – 466 4661 for any further information you may be requiring, he is based in Nelspruit, Mpumalanga.