Groundwater Level

Foundation construction is complicated by groundwater flowing above the bottom of the proposed foundation level. In such cases the sides of the excavation may be undermined and cave in. Lowering the groundwater level by pumping the water out of the excavation usually requires the installation of braced sheathing to shore up, or retain, the sides of the excavation to prevent any cave-ins. When the amount of water within the excavation is excessive, ordinary pumping methods, which bring to the surface loose soil mixed with the water, can undermine the foundations of buildings on adjoining property. To prevent damage caused by soil movement, wellpoint dewatering is often used. Wellpoints are small pipes with a perforated screen at one end. They are driven or jetted into the ground so that the screen, which prevents soil from flowing in with the water, is below groundwater level. These pipes are linked to a common manifold (pipe) that is connected to a water pump. In this way the groundwater is removed from below the excavation without damaging nearby property. Dewatering may also make it unnecessary to sheathe the sides of the excavation, providing the soil will not slide into the excavation because of its composition or because of vibrations from nearby heavy traffic or machinery.

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Дата добавления: 2015-08-27