Single-Walled Cofferdam
A single-walled cofferdam is used where the area to be enclosed is very small. Therefore, it will be best when available working space is limited. This type of cofferdam is used for depth of water up to 6 m.
First of all soft materials are removed from the bed of the river. Then, a row of guide piles are driven into the ground along the periphery of the area to be enclosed. These guide piles are usually driven at an interval of about 3 m. The distance between the two guide piles depends on the depth of water and the size and length of wales available.
Generally, the guide piles are made of wood, but it may be a steel section in case of large depth of water. After having driven the guide piles, wales or runners of timber logs are bolted to the guide piles at suitable vertical intervals.
Finally, sheet piles are bolted to the wales. Sheet piles may be made of wood or steel. The lower end of the sheet piles is driven into the ground for some depth. It is essential to keep the sheets vertical.
In the case of steel sheet piles, the lubricant must be applied to the interlocking parts before it is assembled.
If the depth of the water is quite large, then additional wales may be used and a framework of struts and bracings installed to keep all the members held together.
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