HYSON-CELLS

This section covers the construction of geo-cell walls and aprons for constructing retaining walls, lining channels, revetments and other anti-erosion structures.

The plastic to be used in the manufacture of geo-cells shall be High Density Polyethylene (HDPE) film 0.2 mm thick (with options varying between 0.15 to 0.4 mm), not UV resistant. The sheeting shall have a smooth finish and shall not be textured. (A textured finish will interfere with the desired rotation within the joint under loading).

Geo-cells manufactured from permeable materials such as textiles are specifically excluded as an alternative, because the resulting bonding will not result in a joint equivalent to that of the specified geocell).

Rigging String to be Polypropylene Baler Twine for contractors UV resistant.

All wire used for making the joining nails shall be 2,6 mm in diameter and shall comply with the requirements of SABS 675 or equivalent of mild steel wire.

Anchor pegs shall be made from deformed high tensile steel rods, 10 mm or 8 mm in diameter according to the softness of the underlying material. The rate of application of pegs shall be 1 per square metre for the main area and 1 peg in every second cell in "tuck-in" terminating anchor trenches. The length of each peg is determined according to the in-situ material but shall not be shorter than cell depth plus 100 mm. The anchor peg steel shall comply with the requirements of SABS 920.

Cement shall be ordinary Portland cement, which complies with the requirements of SABS 471 or equivalent.

Use of additives such as plasticisers and retarders are encouraged but must meet with Hyson-Cells’ approval.

Sand for concrete, cement slurry and cement mortar shall comply with the requirements of SABS 1083 or equivalent.

Sand for blinding used for geo-cells mats shall not contain any deleterious impurities and shall be well graded.

The stone to be used with geo-cells shall be clean, washed and single sized road stone, generally complying with the requirements of SABS 1083. Stone shall preferably be 9,5 mm or 13 mm.

Concrete work shall be carried out in accordance with the provisions of Section 6200, 6300 and 6400.

Geo-cells is a three-dimensional honeycomb mat made from 200 micron plastic sheeting. The geo-cells are manufactured by heat sealing polyethylene film to form a three dimensional honeycomb mat, comprising connected, square, hollow, thin-walled cells. The cell mat must be supplied with integral pre-strung rigging.

They come in two types:

Shallow cells generally used as in-situ formwork to cast slabs of connected interlocked block paving, the cell formwork remaining in the slab to serve as jointing and to release hydrostatic and pore pressures, or in more than one layer generally used for the construction of retaining structures.

Deep cells that can be several metres high and can be used to reinforce granular soil fills by the action of containing it.

Sufficient rigging string and pegging steel rods for all the tying and pegging of the geo-cell mats shall be supplied during the construction of the geo-cell structure.

The tolerances for the length of the mats shall be ± 10 %, for the width of the mat ± 5 % and for the depth of the mat ± 5 %.

The surface on which the geo-cell mats are to be laid prior to their being filled with concrete slurry or sand, shall be levelled to the depth shown on the drawings or as erected by the Engineer so as to present an even surface. Where required, a foundation trench along the toe of the revetment or wall shall be excavated to the dimensions shown on the drawings or indicated by the Engineer.

The methods of constructing, stretching, placing in position and filling the geo-cell mats with slurry concrete or sand or rock shall generally be in accordance with the manufacturer’s instructions which have been approved by the Engineer. The following is emphasised :

It is essential that the Contractor ensures that the cells are rigged extremely taut. Rigging strings are not to be omitted. Rigging and pegging are required to prevent collapse of the cells during filling, to prevent the cells floating on the concrete and to ensure an intimate contact of the cells with the base.

Note that the use of rigging with geocells is the subject of certain South African patents held by Hyson Cells.

Packs shall be joined to each other as per manufacturer’s instructions. It is not permitted to simply butt one pack against another else a weak construction joint will be formed.

Geocells which do not butt to kerbing or similar will terminate in "tuck-in" terminating beams to the dimensions shown on the drawings or indicated by the Engineer. The geocells shall be feathered into the terminating beam to a minimum penetrating depth of 150 mm.

Hyson Cells written instructions are augmented by on-site demonstration.

The layout and the tolerance for the layout of the geo-cell mats shall be as shown on the Drawings/Specifications or as indicated by the Engineer.