Water in your excavation or foundations: what to know and prepare

On Qatari sites there are usually three sources. In parts of the country groundwater sits close to the surface, so it seeps into a pit as soon as the dig goes below it. Rain, even a single heavy shower, runs off the surrounding ground into the lowest point on site, which is often the excavation. And a damaged water main, irrigation line or sewer nearby can flood a trench overnight.

The source matters because it decides the fix. Rainwater is a one-off that can be cleared once. Groundwater keeps coming back and has to be managed for as long as the excavation is open. A leaking pipe has to be found and stopped, or the water will simply return.

Water stops work. Concrete can't be poured into standing water, waterproofing won't bond to wet surfaces, and inspections wait until the formation is dry and visible. Water also softens the ground at the bottom of the pit and can weaken the sides, so the longer it sits, the more rework there is once it is gone.

Muddy water is worse than clear water. The silt settles as a soft layer at the bottom that has to come out as well, which is why the removal method should lift the mud, not just the clear water on top.

Check the site investigation report for the groundwater level and build water removal into the programme from the start, rather than treating it as an emergency. Agree with the client and the consultant how water will be handled, and follow the project's and the authorities' rules on removing it. Water must never be pumped onto the road, into a storm drain or onto the next plot.

Plan access for a large, heavy truck: a firm route in, room to turn, no low cables, and a place to stand on solid ground well back from the edge of the excavation.

Nobody should work in or enter a flooded trench or pit. Water hides the depth, the footing and any collapse at the bottom, and wet sides can give way without warning. Keep the edge protection in place, keep people and plant back from the edge, and don't stack materials or park vehicles close to it.

Electric pumps and cables in or near water must be properly protected and checked. Deep pits, lift pits and manholes can also collect harmful gases, so treat them as confined spaces and follow your site's safety procedures before anyone goes in.

For steady seepage, many sites run their own submersible pumps or a dedicated dewatering system while the foundations go in. A suction truck is the better tool when the water is deep or full of mud, when a basement or lift pit has flooded, after heavy rain, or when there is nowhere on or near the site to send the water.

Our dewatering service uses the Super Combi to lift water and mud out of the excavation into the truck's own tank, so it leaves the site with us. We can come once, or on agreed days while the below-ground work goes in. After heavy rain, the same truck works on our rain emergency calls, and if mud has spread onto site roads or compound streets, our road sweeper clears it through street and compound cleaning.