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Name: Mohammed
Status: student
Grade: 4-5
Location: SC 
Country: N/A
Date: 2/21/2005


Question:
How are the excavation jobs done in underwater sites like a bridge footing?


Replies:
More often than not, the foundation is either something drilled like a pier. The drill operation "casing " the hole. The spirals on the drill push the material back out and a steel tube surrounds the drill. Later, depending on the hole, water can be pumped out, or just pouring concrete will displace the water. Some piers are just concrete, but most have a cage of reinforcing bars inserted into the concrete to give added strength.

Other foundations are H pile, or other beams, whether made from concrete or timber ( similar to telephone poles). These beams, or think columns, are driven into the material. The material can be soil but it also can be rock. A group of what you can consider columns are the embedded support.

You can excavate underwater, but the material will slide back into the hole, so usually sheet piling is drive, to form a box, then the material inside excavated.

As you can see, there are a lot of calculations to attempt to predict not only how the material will behave but what you are inserting, or doing. That is engineering, structural dealing with the new items. Geotechnical, or soil engineers dealing with the existing, whether soils, or rock ( geologists dealing with rock properties.

James Przewoznik



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