Griffin Dewatering

Geotextiles in Construction Dewatering

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Courtesy of Courtesy of Griffin Dewatering

Woven geotextiles work wonders in dewatering applications as wraps around well screens and sump pit screens. The textile can be sewn into sleeves or tubes to be slid over the well screen or sump pit framework. This technique allows the user to compensate for well screens with slots that are too large or for sump pit piping with large perforations. By adding the geotextile sleeves the user can select a finer grade of filter pack or gravel pack more closely suited to the surrounding soils, i.e., use a finer weave geotextile in silty and clayey soils. These soil types wreak havoc on construction sites plugging up drain pipe, sewers and wearing out pumps. Municipalities plagued with the problem of cleaning out storm and sanitary sewers plugged with sediment from new construction sites have levied heavy fines on the contractor at fault, making geotextiles an attractive preventative maintenance alternative.

Non-woven geotextiles tend to be more adaptable to variable soil conditions particularly in areas of glacial development where the soil profile changes from random deposits of very fine silts, clays and sands to coarse sands, gravels, cobbles and boulders. The non-woven material has thickness which reduces the tendency for soil 'bridging', which is soil particles interlocking to 'dam' up the open channels in the filter thus blocking water flow. Over the last twenty years the strength and tear resistence of non-woven geotextiles has been greatly improved allowing for installation in long segments. Installed vertically to depths of 60 feet and deeper geotextile assemblies create 'water wicks' removing water from unstable soils to induce natural compaction. This passive application is permanent and protects new structures from upheaval and settlement. These geotextile wicks allow the soil to adjust to changing water table levels without removing fine particles of soil in the process.

Non-woven geotextiles attached to the proper support structure or framework are used routinely today on below ground building walls to channel ground water and rainwater runoff away from the walls to collect piping, thus eliminating seepage into the building basements. The same principle is being applied to temporary and permanent construction dewatering systems. This relatively new approach produces fast, clean results eliminating turbidity in the discharge water and, with the proper installation, eliminates the need for using a filter sand or gravel around wells or wellpoints. This innovation gives the contractor the ability to adjust to changing ground water conditions with less guesswork, faster installation, lower labor costs, less down time and happier environmental managers.

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