Sheet Pile Wall Structure Designs on Seriously Weathered Rock Layer

For sheet pile wall or cofferdam construction, normally we need to drive piles to the required depth. But for shallow layer especially seriously weathered rock layer, it is very difficult to drive piles. For instance, top surface of highly weathered rock and sand layer is 1-4m lower than cushion base, and some part is even near the cushion base. Because the driving depth is not enough as required, the displacement at the pile-end will be larger, sheet piles in some project sections would easily get damaged like "kicking damage".

For this problem, we must take some measures on structural design first.

For structral desgin of sheet pile wall, there are mainly three plans to solve the problem :

1. Enlarge the wall or cofferdam and put slope inside;

2. Increase inside support layers;

3. Reinforce the bottom of sheet piles;

Sheet Pile Wall or Cofferdam

Comparing three plans above, if only by plan 1, because the wall or cofferdam is normally large enough, it will cost extra money or time. And if there are more wall or cofferdams in construction at the same time, it will influence other projects too; Just by plan 2, if we increase inside support layers when excavation near the end, supports' changing process will be more complicated when it comes to the back concrete cover; If just by plan 3, although it is applicable in theory, it is not enough for pratical construction.

The best way actually is to combine the strong points of the three plans. For instance, firstly, we can set the axis line of sheet pile wall near the cap side which will proive a certain slope space and is useful for sheet pile reinforcement.Secondly, set 6 layers of inside support,make the space wider at the upper 4 layers. At last, at the location higher than layer elevation of 7.0m, set steel tubular pile (or called steel pipe pile) as support foot right near the driving-hole of sheet piles.