There are fewer better examples of land reclamation than those found in the Netherlands, with hundreds of kilometres snatched back from the clutches of the Zuiderzee. It’s this legacy, which has been absorbed and passed on by the mother company of Koop Water Management Middle East (KWMME) in the Netherlands, which best benefits in Qatar – a respected dewatering expert in its own right.
Qatar’s geology features a high water table that sometimes rises to above the ground’s surface. It is this natural phenomenon that poses a threat to any type of construction in the country, often requiring extensive dewatering systems.
Marc Dinnematin, business unit head, KWMME, describes some of the challenges faced in the dewatering sector, and specifically in the roads and infrastructure project south of Doha in which KWMME is presently engaged. The main contractor’s scope entails pipe laying for the storm water drainage and sewage works.
A sub-contractor on the project, KWMME’s job is to supply dewatering services for micro-tunnelling shafts and open trenches for this pipe laying, which requires a dry environment.
The entire dewatering site comprises an area of around 3km², with approximately 3,200m³ of water pumped out per hour, from the lagoon to the sea. The micro-tunnelling shafts measure 6m by 6m, ranging from depths of 12m to 18m. Although there are a total of 81 shafts throughout the area, as the dewatering progressed, it was found that fewer shafts require dewatering, dropping the number to 50.
“Because we are seeing a drop in the average water table level in the area, some of the shallower ones don’t need dewatering,” he says.
At the start of the project, the volume of water that required dispersal or removal was unexpected, as Dinnematin explains: “In the beginning, as we were the first company to dewater this area, the ground was fully saturated, which we realised when we sunk the first shafts, which filled with water.
“The flows were huge and, because of the unpredictable character of Qatar’s geology, we encountered numerous cavities, more than on any other project previously. When we did our soil investigation, while we were aware of them, the number was greater than what we expected.
“With the soil investigation report, the boreholes were made all over the area, scattered, but [it was] difficult to predict how fractured the layers were, which allowed in more water. Some shafts had fewer fractures or fissures, while others had gaping fractures that allowed water to pour out.