Galvanized Steel Gabion for Cofferdam Slope Protection

The galvanized steel gabion slope protection and the stone slope protection are the main construction for the cofferdam slope of water conservancy. The range for the galvanized steel gabion slope protection is from 35.3 m upstream cofferdam to 35 m downstream cofferdam. The standard specification of the gabion is 6 × 2 × 0.23 m. The galvanized steel gabion which stands on the left of the cofferdam is 6 × 2× 0.30 m. According to the demands, the thickness of the galvanized steel gabion which lies in the left of the cofferdam is 30 cm. The thickness on the upstream and downstream cofferdam is 30 cm. The following is the construction table.

A white gabion mattress surrounds around a river and filled with rocks. On the back of the mattress is a forest.
Galvanized steel gabion is for slope protection.
Table 1: The cofferdam slope protection construction standard
The position The galvanized steel gabion {m3(m2)}
The upstream cofferdam 5295 (23020)
The downstream cofferdam 5762 (25050)
The left vertical cofferdam 4350 (14500)
Note: the horizontal thickness: 23 cm, the vertical thickness: 30 cm

The construction difficulties.

  1. The cofferdam soil filling construction schedule is usually hysteretic and there is the flood control pressure. The slope protection and the soil filling construct are at the same time. Thus there must be the serious field management and scientific construction arrangement.
  2. There is much terrain height difference on the cofferdam filling, especially on the left and right shore segment. When we construct for the galvanized steel gabion slope protection, firstly we should find the straight line for the slope toe according to the terrain. We should make sure the slope surface is neat and the galvanized steel gabion construction is perfect and owns its aesthetic.
  3. We should make sure that the stone slope protection is according to the technology and the geotextile would not damage and displace.

The construction process for the cofferdam galvanized steel gabion slope protection.

Mend the weir slope, smooth the slope toe, put the non-woven, install the galvanized steel gabion, fill the galvanized steel gabion with stones, fix the cover panel and the steel, repeat the process until we finish installing the galvanized steel gabion slope protection.

The galvanized steel gabion construction feature, technology and ways.

The galvanized steel gabion slope protection construction feature and technology.

  1. The galvanized steel gabion slope protection construction feature.
    • There are many tasks while the schedule is tight, and the flood control pressure is high. Not only the backhoe helps to construct but the artificial installing, artificial filling and artificial putting are needed.
    • The surface of the protection construction is neat and beautiful. The stone filling is plump and the gap between the stones should be according to standard.
    • The construction area is big and the construction schedule is long. It's hard to prepare the all the materials.
  2. The galvanized steel gabion technology.
    • The specification of the gabion: 6 × 2× 0.3 m and 6 × 2 × 0.23 m. It owns high corrosion resistance and is of low carbon. There is a partition panel to divide the gabion with the small units every 1 m. The tolerance for the length, width and height is ±5%.
    • There are two partition panels for the galvanized steel gabion. Except the cover panel, the side panel, the bottom panel and the partition panel could not be divided.
    • The tolerance of the galvanized steel gabion length and width could be ±3%. The height tolerance is ±2.5 cm.
    • The mesh opening is 6 cm × 8 cm. The diameter of the steel wire is more than 2 mm and the diameter of the side steel wire is more than 2.4 mm. The diameter of the twisted steel wire is more than 2.2 mm.
    • We should wind the steel wire mesh to the edge steel for more than 2.5 circles with the professional flanging machine.
    • For the galvanized steel gabion steel, its tensile strength should be more than 350 N/mm2, its elongation is more than 9%. The shortest steel of the steel samples is 25 cm. The tolerance of the steel diameter is ±0.05 mm, and the tolerance of the side steel is ±0.06 mm.
    • The standard for the steel quality: the service life for the galvanized steel gabion is four years and its coating layer would not crack for four years.
  3. The filler quality and the technology demand.
    • We use the stones or the pebble as the filler. The diameter of the stone is 80–150 mm and only 15% stones' diameter could be less than 80 mm. But this 15% fillers could not be the first filler layer of the gabion. The filler should be hard and the strength grade is MU50. The hardness is 3–4 and the proportion is more than 2.5 t/m3. The filler would not crack or weather.
    • We should not use the sheet or the stripes stones. The weathered rock and the mudstone could not be the fillers.

The galvanized steel gabion construction.

  1. Repair the slope surface.
    We repair the slope with the machine and tamp the slope. We clean the slope surface so that the slope meets the design.
  2. Putting the non-woven.
    • We should inspect the surface and make management for the non-woven. We should make sure there are not debris and the surface is neat.
    • The connecting for the non-woven should be jointed with the sewing machine when we put the non-woven. The connecting for directed slope could use the butterfly shaped and the connecting along the slope could use flat shaped. The connecting should be according to the standard.
    • We should put the non-woven from the top to the end. There is 0.3 m left on the edge of the non-woven to firm so that the non-woven would not slide.
    • We should not pull the non-woven too hard and the non-woven should be smooth. There is not gap between the non-woven and the soil surface. After the non-woven is installed, it should not be exposed on the sun and we should install the galvanized steel gabion in time. If necessary, we should cover for the non-woven.
    • We should pay attention to the mechanical or artificial damage for the non-woven. We should repair the broken non-woven in time.
    • The quality of the non-woven should follow the technology standard. The sampling rate should be more than 5% of the delivery quantity. We should do the measure control and make the construction report for the quality assessment basic. We should firstly inspect for the slope repairing, non-woven installing and galvanized steel gabion installing when we are going to start the next construction process.
  3. The transport for the galvanized steel gabion.
    The galvanized steel gabion and its parts should be according to the ASTM A975-97 standard. During the transport, the galvanized steel gabion should be unfolded and tiled. The partition panel and the edge panel should be folded. By this way, it's easy to transport the galvanized steel gabion.
  4. Install for the galvanized steel gabion.
    • The professional workers should guide the installation for the galvanized steel gabion.
    • We take the folded unit and put it on the neat ground. We open the unit and find its original shape. We fold it from the side along the line and connect the folded part. We should install the galvanized steel gabion one by one. We should keep the folded trace on the right position. The side, the tail and the partition should be erected and the top part should be on the same level.
    • We should connect the galvanized steel gabion with the twisted steel wire. The way we use the twisted steel wire: Firstly we cut off a length of steel wire and put it on the grid and twist. We tighten the single and double knots every 150 mm on the metal grid. Finally we should firm the end of the twisted steel wire on the metal grid. We should settle the partition vertically and connect the partition and the side panel with steel wire.
    • The assembled galvanized steel gabion owns regular shape, its line is straight and the knot is firm.
    • The long edge should be perpendicular to the slope.
  5. The construction of the bottom galvanized steel gabion slope protection.
    • The bank is rugged so when we install the bottom galvanized steel gabion we should install according to the original terrain. We can install the galvanized steel gabion section by section and clean the slope. For the flat road, the section is 50–100 m. After repairing, the slope toe line should be neat.
    • The bottom gabion construction line should be parallel to the top of the cofferdam. We should make sure that the galvanized steel gabions are arranged tightly.
    • The galvanized steel gabion filling construction.
    • We should prevent the non-woven from damage.
    • We should fill the gabion from the bottom slope to the top slope with the machine and artificial auxiliary.
    • The gabion should be full of the stones especially on the four angles and the partitions. The gap rate cannot be more than 35%.
    • We should clean the surface and the smooth face of the stone should be upwards.
    • The filler could be 15–25 mm taller than the gabion height for the stones maybe settle.
    • Inspect the stones filling and cover the top panel. We should firm it with twisted knot. We should twist the cover edge and the bottom edge. The interval of the steel twisted knot should be 15 cm according to the single and the double circle.
  6. The not standard galvanized steel gabion construction.
    • On the connecting of the left vertical cofferdam and up-down stream horizontal cofferdam, the galvanized steel gabion specification may not follow the standard. We should cut down the gabion according to the standard so that there is not too much gap between the gabions.
    • Sometimes the galvanized steel gabion of the left vertical top cofferdam and the bottom cofferdam doesn't follow the standard. We should fold the gabion at the scene and make sure there is not much gap between the gabions.

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