[On Demand Webinar] How to Plan to Dewater Your Construction Jobsite
Webinar Video Presentation Teaches Construction Professionals the Dewatering Planning Process
Get a head start on the process of managing a dewatering project on your jobsite with the insider tips provided to you from our seasoned Rain for Rent dewatering experts and in-house Engineering Dept.
Gain knowledge from a pre-recorded Q&A session from like-minded industry pros.
Webinar topics discussed include:
- • Overview of Dewatering
- • Gathering Key Information
- • Methods and System Design
- • The Need for Case Studies
- • Q&A
How to Plan to Dewater Your Construction Jobsite
Dewatering is the removal of water from an excavation site. Why is dewatering necessary? Because it allows work to proceed in dry and stable conditions.
Planning construction site dewatering takes careful planning, analysis, and the right dewatering equipment.
Types of Dewatering Systems
Reduce delays and save money with the right plan to dewater a construction site. You can either block water from the excavation area or draw water away from it. The first method uses cut-off or slurry walls to limit the pumping required. The second method uses dewatering equipment like wellpoints, deep wells, and sumps. Drawing water away from an excavation site is often the most cost-effective option.
A wellpoint dewatering system addresses recharge from both local and remote sources. The system requires shallow wells that are close together. In fact, spacing ranges from as close as a foot to 15 feet, with 6 feet being the average. With well-point depths of up to 29-feet, groundwater can be drawn down to 17-20 feet at sea level. The ideal wellpoint system extends around the entire perimeter of the excavation site. Wellpoint systems are scalable. Use more header pipes, pumps, and points to handle larger sites and higher flow rates.
Wellpoint dewatering systems handle a wide range of soils, from fine to coarse, and from uniform to stratified. They also tackle a wide range of flow rates. It is possible to design a wellpoint system that handles less than 0.1 GPM in clay soils to as much as 20 GPM in coarse, gravelly soil.
Since many points are required, quick, efficient installation is essential. This is most often accomplished with jetting. High-pressure water punches a hole in softer soils. In firm soils, it is necessary to use a driller.
Like wellpoints, deep wells handle recharge from both nearby and remote sources. Deep wells can be hundreds of feet deep. They work especially well in conductive materials like sand or gravel. However, they are not as efficient in fine clay soils. Deep wells are farther from each other than wellpoints. They are often 30 to 200 feet apart – about 50 feet on average.
Crews install an electric submersible pump at the base of each well. Flexible hoses connect the deep wells to the header pipe. Some deep well systems handle high flow rates of tens of thousands of gallons per minute.
Keep in mind that the drawdown is slower with deep wells and close spacing is required whenever there is a nearby source of recharge. Therefore, it is important to synchronize deep well installation with the timing of the excavation.
Sumps have long been a traditional option. Crews build barriers to keep water out of the excavation, and they dig trenches to route water to collecting areas. From there, pumps remove it from the construction site. A shallow sump requires a trailer-mounted pump, while deeper ones use submersible pumps.
The sump system is quick, inexpensive and there is no pre-drainage delay. Unfortunately, it is somewhat slow, and it cannot always cope with higher flow rates.
Construction pros need to know whether renting or purchasing is the best move.
Learn more about the pros and cons in this article.
Which System is Best for Your Project?
A successful dewatering system delivers a dry zone needed for safe and efficient excavation. This zone usually extends two or three feet below the excavation’s lowest point, although some prefer five feet.
Groundwater elevation and flow rates impact well design and construction. A good dewatering plan also accounts for variations during the project. Is there the possibility of serious runoff following heavy rains? Are nearby waterways prone to flooding?
There are several questions to ask when choosing the best dewatering system for your project. Are there nearby structures vulnerable to the lowering of groundwater? Will soil contamination complicate water filtration? Proper water filtration is key. The discharge permit determines the scope of filtration. Is the ground so hard that jetting is not an option? This will impact the cost of a wellpoint system.
A sound dewatering plan requires a competent analysis of bore logs, geotechnical reports, and water quality reports. A slug test or a pump test provides additional valuable data. A slug test allows dewatering analysis from a single well. It is simple but typically not as accurate as a pump test. By contrast, a pump test requires the drilling of a test well and various observation wells. A pump test establishes a “radius of influence.” Find out how effective your dewatering equipment will be as you get further from a well.
Finally, keep in mind that lowering groundwater to required levels often takes one to three weeks.
Let Rain for Rent Help You Plan Your Dewatering Project
With variations in site elevation and size, no project is exactly the same. We can provide virtual consultations or physical job walks to help you spec out the equipment needs you’ll have before you break ground as well as help in emergency situations. Contact Rain for Rent to get a quote or learn more about how we can help.