Dewatering is a necessary evil in construction. “Keeping a dry hole is definitely required and necessary to maintain a smooth construction schedule,“ says Ken Albaugh, who leads the dewatering commercial team in North America for Xylem, a global water technology player.
Dewatering lowers groundwater levels within the vicinity of the excavation. But a one-size-fits-all approach to dewatering a construction jobsite simply won’t work. “Each site is a truly a unique environment,” says Albaugh.
Paul Schmall, vice president of Keller Specialty Services with Keller North America concurs. “A site-specific evaluation, including historical records if available, and a local understanding of the groundwater behavior is vital to determine the optimum solution,” he says. “If groundwater control is a critical path activity, this is not a good setting for do-it yourselfers and certainly not for first-timers. Experience is paramount.”
Sump Pumps
Sump pumps are a common dewatering solution for construction sites. Groundwater enters the site and is collected in a sump or pit and removed using powerful pumps that can handle not only water, but soil and other solids.
“The contractor has to know how much water is coming into the hole, and how fast,” says Tony Chirico, national sales manager for Gorman-Rupp Company. “That will help narrow down the size of the pump required for the application along with calculating the TDH (total dynamic head).”
The type of material you are pumping will influence the type of pump used as well as the pumping distance. “For example, when pumping water mixed with sand or silt you might want to choose a pump with hardened components or coatings,” says Chirico.
According to Chirico there are three primary types of pumps used in the construction market: self-priming pumps (wet prime), prime-assisted pumps (dry prime) and submersible pumps. Self-priming pumps require water to prime and reprime, while prime-assisted use an external priming device (compressor/venture, diaphragm, and vacuum style) to prime and reprime. “Prime-assisted (dry prime) is typically a product of choice for most rental companies and contractors alike because of its ease of priming and run-dry capability,” says Chirico.
Wellpoint systems
Some sites may require 24/7 pumping if the water table is higher than the excavation subgrade. On these sites the water level can be lowered to create a safe, dry environment for excavation using wellpoint pumps and piping. A wellpoint system features wells which are spaced around an excavation and connected to a common header, which is attached to many more wellpoints. According to Schmall, they are best suited to relatively shallow excavations (less than 15 feet) and can be installed in a wide range of soils including sands, gravels, silts, soft clays and stratified soils.
Deep wells
Deep well dewatering is typically utilized with deep excavations, where the height of static water above subgrade is greater than the typical 17-foot suction lift limitation for a wellpoint system. Tunnels and dams are good examples of deep dewatering work.
Wells can vary in size from 3 to 24 inches in diameter and range in depth from 20 feet to several hundred feet. Each deep well holds a submersible pump. By operating deep wells around the vicinity of the excavation site, the groundwater can be lowered without equipment in the hole, a major advantage for the general contractor.
Cut-off
Another dewatering method that can sometimes meet requirements is installation of a cut-off where a barrier excludes water from the excavation area. “Cut-offs can take several forms such as barrier walls made from steel sheeting, “chain saw” trencher soil mix walls, conventional slurry trenching, or diaphragm walls for deep excavations,” says Schmall. “Jet grouting and permeation grouting are also options.”
Dewatering expertise
According to Schmall, “any project that is less than straightforward, where there is no tolerance for a “hiccup”, or when multiple options are available to achieve the desired result, should involve a ground engineering specialist. An experienced groundwater control engineer can also weigh the options of dewatering vs groundwater cut-off such as steel sheet piling or a soil mixed barrier wall.”
Xylem’s services cover a wide spectrum and depending on client needs, they will provide anything from rental equipment to complete turnkey services. “I’m seeing growing demand for turnkey solutions,” says Albaugh. “Anybody can rent a pump. We try to be that partner that will give them a solution on how to dewater at an efficient cost.”
No matter what dewatering system is utilized, contractors need to be mindful of local discharge requirements and regulations. Water quality can be changeable too depending on site activities. Technology is allowing contractors greater control over releases of dirty water. “We can now put sensors into the pipelines to check for PH and turbidity,” said Albaugh. We can change the turbidity to make sure we are not releasing dirty water.”
Connected technology improves efficiency and maintenance
Smart technology now allows contractors to monitor pumps remotely. “We can see when we have a dry or wet hole from our smartphone” says Albaugh. Weather monitoring systems can trigger the pump to speed up or slow down to meet the conditions.
“Contractors want a reliable pump without too much maintenance and they want to get it started without any additional resource,” says Chirico. Remote access through telematics allows them to easily check to see that pumps are properly maintained and fueled. Rental companies can see where their assets are located and how many hours they are being run.
According to Schmall other advances that the ground engineering community has seen in recent years last few years include the effective combined use of partial cut-off and pumping as well as innovation in drilling techniques. It is now possible to install angled wells, horizontal wells, wells from inside tunnels, from basement interiors, and to drill wells into rock and difficult conditions.
With technology expanding your options, this may be the year to look at strategies to dewater your jobsites with an eye toward improving efficiency, reducing pump maintenance costs, and keeping projects on track.
Brands Featured in this Article:
Join more than 40,000 industry peers who receive construction industry news and trends each week. Subscribe to CONEXPO-CON/AGG 365.
