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5 techniques for successfully Dewatering Shafts and Tunnels

by SPIN PRO Business
There are different methods used for controlling ground water during excavations. Choosing the right dewatering process is an important step in any construction or mining project. This is because every project has a unique set of ground conditions that must be carefully assessed. When choosing a dewatering method, it is crucial to reduce the impact that the technique will have on the ground water resources.

Eductor wells

The eductor well technique is a dewatering process that is used to control the pore water pressure in materials that have low permeability characteristics, for example, silts and fissured clays. This technique utilizes the venturi principle and is the most efficient method of lowering the ground water levels in silted and sandy areas. With this system, high-pressure water is circulated through the eductors through the base of every well, thus creating a vacuum that helps in promoting drainage.

Sump pumping

The sump pumping technique allows the ground water to percolate in the excavation area, where it collects in sumps and is then pumped away through high-powered, solid handling pumps. This technique is usually used in areas with shallow excavation. Sump pumps have the ability to handle a little solid while moving water. This technique comes in handy for relief well dewatering because these wells are usually filled with gravel or sand to create a permeable path to areas where sump pumps will have access to. Sludge tubes come in handy in areas that have lots of sludge.

Wellpoints

This dewatering technique uses lines or rings of closely-packed wells installed around the excavation spot. The wellpoints are connected to a headerpipe that is pumped by the wellpoint pumps which can handle both air and water. This dewatering system usually works in stages. It can regulate the ground water level at only about 15-18 feet below the wellpoint pump heads. For tunnel excavation that is deeper than this, it is best to install another ring of wellpoints that are at a depth which is equal to that of your initial set.

Deep wells

Electric submersible pumps will lower the groundwater level that is below your tunnel. The pumps are usually installed in the wells that are drilled outside the perimeter of your excavation area. This technique is ideal if you want to lower the groundwater level due to deep excavation. Deep-well dewatering tends to be less effective in soils that have a low permeability that limits water flow. Most submersible pumps are unable to handle low flow rate. In such a scenario, dewatering using eductor wells is a perfect choice.

After choosing the right dewatering process for your shaft or tunnel, you will need to dispose off the wastewater. The right polymer make down systems can help you out when it comes to disposal of wastewater. However, you should keep in mind that if you use the sump pump technique, this water must undergo treatment to eliminate the solid part.  Consider the local regulations and rules regarding discharging water before you start any disposal.

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Created on Aug 8th 2018 02:16. Viewed 265 times.

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