bore pile wall

[olaf]

I need some advice to choose the right retaining / supporting wall system.

We have to discuss this problem with our geotechnical and structural ingeneer but want to get an idea for our own what is possible. I searched the forum first and found a lot
of informative hints but my case seems to be a little bit special.

we have to deal with an existing retaining structure of around 120m length for a 10m jump in terrain heigth in a historical town setting. The structure consists of 3 rows of walls. The overall visible wall height is around 7,5m. The width of between 1st and 3rd wall is
around 10m

Wall Material is sandstone but the foundation is unknown. Seems that the whole wall are only gravity walls. Ground layer is poreous sandstone with 1,5m soil cover.

On top, in 3m distance from the last wall a 1-storey building is located.

This is the situation for the last 50 years.

Around 50m wall consist of remainders of former brick masonry wall in very bad conditions.

This 50m "gap" must be closed with a new wall to get a good overall look of the structure.

What creates uncertainity is 1) a small soil hill on the toe side of the brick remainders (no idea if purposly put in this place or not)

Due to a new development the house must be appoached by the fire fighters with their trucks (the driveway ends 10m from the upper wall).

So far the description - now the problem !

we have to prepare a decision about what could be an appropriate wall type and foundation.

A first suggestion we got was a bore pile wall. The idea behind was to create a main supporting structure on the 1.level and to reconstruct the other 2 levels as "simple"
gravity walls.

But in my eyes this seems me a bit to much effort compared to the current situation, where the existing wall holds the terrain for a long time.

So what other possible solution are worth checking in terms of costs and technical feasibility to reach the necessary
stability (probably the threshold for this is higher today
than in former times)

At the end what is are suitable methods to discover the wall structure itself and the foundation.

Is a good reading material available that covers some basic of this area?

Thanks

Olaf

 

[Focht3]

Olaf -

You did a commendable job in describing the problem even if you are not an engineer. I will try to address your question, but my answer includes some assumptions:

1. You don't want to damage the house.
2. The engineers are concerned about excavating too close to the house.
3. The owner of the house - and historic distric leaders - do not want the appearance of this area to change too much.
4. The 50 meters of brick wall are at level 1 or 2.

A bored pile wall (also called a drilled shaft wall) would be ideal for your problem. And it should be at the lowest level if possible. The new completed wall will have a pivot point just below the top of the sandstone, and the wall must extend into the sandstone far enough to hold horizontal forces exerted by the soils and house. If you double the height of the wall, the torque or moment on the wall will go up about 8 times! You want to make the wall as short as possible.

You also want to keep the drill rig as far away from the house as possible to avoid damaging the house foundation. A diaphragm wall would also work but involves a lot more risk of failure during construction.

Based on what you have told us, it sounds like your engineering consultants are giving you good advice.