Rockfill Cofferdam, that is, use local available building materials as the main filling material;
It is a traditional earth-rock cofferdam. The local earth and rock materials can be used, taking into account the main pumping station was built after the project finished as a permanent sea wall, so that it could be a part of eastern north berm project.
But if we use solutions of ordinary rockfill cofferdam and rockfill cofferdam in the heart of sheet piling wall , there does not have enough space in such a narrow range of grading.
Secondly, cofferdam construction required fast speed in building, but in these types of programs, large amount of rock and serious slippery preloading can not be too high too fast.
Thirdly, as pit depth is down to -20.8m, according to requirements from excavation design unit , the seepage control depth of cofferdam is better to deep clay layer to -13m, slope can not be stabilized within the ordinary rockfill cofferdam and excavation can not meet requirements.
Furthermore, outside the cofferdam, the water is deeper so that velocity and wave is more serious and erosion is more severe, so outside of the slope, it is not stable either. Especially if cofferdam foundation is not treated on soft ground, combining with the ebb and flow, it easily results in land shifts, slides and collapse. Then we have to fill and repair frequently because of poor security.
Steel Sheet Pile Cofferdam, that is,use cold-formed steel sheet pile wall to form a cofferdam, and then fill the clay.
The program has advantages of high strength in material, arbitrary length, lower price, light weight per unit, fast construction speed, short project cycle, good security and stability and effectively guard against moisture,waves and seepage.
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