Geomembranes and Water Treatment

Dallas Eastside Water Treatment Facility
Installation:
With the levee embankment already partially encapsulated by the lagoon liner on the inside slope and the surface treatment on top, it was decided to further encase the levee by placing a liner system and surface erosion control on the outer slope.

The slopes were stripped of vegetative cover and graded in preparation for the new slope protection system. An upper anchor trench was excavated along the outside perimeter of the access road at the top of the slope to anchor the various geosynthetic products that formed the liner system and final slope cover.

Based on the findings of the geotechnical engineers, it was agreed that sliding failures triggered by saturation of the deeper soil layers had to be stopped.

The geocomposite liner system consisted of:

• a 40-mil textured HDPE lining,
• a 28 oz. nonwoven geotextile,

and would help maintain even moisture distribution within the levee embankment soils and protect the structure from the major changes in moisture content that were driving the volume change and cracking of the expansive clay soils.

The large cell size enabled Colorado Lining International's installation team to work efficiently on the 3:1 slope face - running tendons - expanding, orienting and then securing the sections.

The installation would also use an erosion resistant slope cover to protect the liner. The Presto Geoweb® cellular confinement system was specified with crushed granite gravel infill for the final slope cover.

The geocellular system was well suited to this application as it restrained the sliding forces of the stone without requiring staking through the liner system. The perforated cells also enabled heavy water flows accumulating above the liner to quickly move down the covered slope without loss of the stone infill.

A deadman anchor system–4 in. schedule 40 PVC pipe–was installed in the trench at the top of the slope and then the perforated geocell system sections were placed. Heavy-duty TP-91 tendons were run through the pre-drilled 4 in. cells and secured by wrapping and tying to the deadman anchor. The use of ATRA® restraint clips spread the working load of the gravel infill from the geocells to the tendons.

An upper anchor trench was excavated along the outside perimeter of the access road at the top of the slope to anchor the various geosynthetic products that formed the liner system and final slope cover.

The waterproof layer of textured HDPE lining was installed over the prepared subgrade followed by a 28-ounce nonwoven geotextile protection fabric.

With the composite liner system in place and tested, installation of the geocell layer began.

The final step involved filling the cells with crushed stone material to provide a final cover for the protected slope.

Upon delivery, a labor crew using long handled rakes spread the materials evenly in the cells.

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