# Connections between RC retaining walls and sheet pile retaining walls

I'm working on a flood defence scheme in which a section of RC flood wall becomes sheet piles. The reasons for this aren't important, but the solution isn't to simply make all walls one or the other.

My issue is how to connect these two very different types of wall in a way that provides an expansion joint for the concrete but is also water-tight. This isn't an issue for connecting individual concrete panels as a waterstop is simply cast into the expansion joint, providing a seal. However, sheet piles don't have anything to 'cast' onto.

My idea so far is to design a sort of concrete (possibly mass, probably RC) 'pilaster' at the end of a section of sheet pile that will allow a water stop to be cast into. However, sheet piles deflect a fair amount which is making me wary of casting a rigid concrete section at the end of the sheet pile.

I'm at a bit of a loss here and struggling to find a precedent of a connection like this. SURELY it's been done before?

I've attached a quick hand sketch. I'm not too bothered about detailed calculations for this; I'm more interested in solving the buildability issues at the moment.

Dimensions are subject to minor alterations but roughly:

• The RC wall penetrates 1.5 m below ground level
• Sheet pile penetrates 6 m below ground level
• RC wall stem is ~350 mm thick
• Sheet pile section is 450 mm thick (AU25 section)

• Do you really need an expansion joint? Couldn't you create a monolithic connection between the two parts? After all, the sheet pile in that direction will behave like a very weak spring, it should hardly resist the thermal expansion of the concrete at all. Also, in describing your pilaster idea, you worry about the fact that sheet piles deflect quite a bit. Given that you need a joint that is stable from construction (when the piles will be vertical) until final load, I think you should actually design this joint precisely so that the piles don't deflect substantially at the joint. Commented Mar 15, 2016 at 16:49

### Similar Situation

I would start by looking at a similar situation in other industries. For this I am thinking about waterproof expansion joints in bridge decks.

The similarities are:

• Relative movements of components
• Waterproof
• Steel and/or concrete

In general this seems to be a pretty good match.

### Products

Some bridge decks have cast-in-place concrete which embeds the joint waterproofing similar to waterstops, but some methods apply a membrane to both sides. This is usually done with enough slack in the membrane to allow for movement.

I have used (but have no other affiliation with) two companies that specialize in this type of waterproofing:

Alternatives may be to use an epoxy adhesive to secure a strip of ~0.5 inch neoprene rubber to each side.

The benefits are that these systems adhere to both concrete and steel. An example detail from Bridge Preservation is shown below:

### Downsides

There are a couple of downsides to these methods.

1. They aren't designed to be structural, so some lagging may be required to support the retained soil/water.
2. They are installed in the field, so construction will be delayed while the system is installed.

We used a simple rubber between two concrete walls. I don't see any reason you can't use the same for a concrete steel wall connection. As these sorts of walls don't settle much you should be ok just coupling these two together without worrying about one settling and dragging the other. Just weld a flat sheet (possibly lined with rubber for water tightness) to the end of the steel one and lowered into the wet concrete.