Existing Retaining Wall Problem

[kieran1]

We have a site where our client wishes to fill with new offices. The problem is the ground level rises from the front street to the rear of the site by 1.7m. Now the site is only 20m long and 12m wide. To complicate matters there is an existing retaining wall at rear of the site. This retaining wall is approx 5.0m high and retains the higher outside ground level. The wall is a masonry gravity retaining wall.

To provide a level ground floor, we had proposed a new secant wall at the rear of the site, in front of the existing retaining wall. This would safegard againest undermining the existing retaining wall when excavating the 1.7m required for a level floor.

The client is not happy with this option. They want us to replace the existing wall and maximise the site area. We cannot get access to the top of the wall and I don't think we can install a secant wall from the lower level. Removing the existing wall would be dangerous.

I can't think of anything feasible for such a small site. We are awaiting the geotechnical investigation.

Kieran

 

[csd72]

Where is the boundary compared to all of this?

Is there enough romm behind to drive sheet piles.

Alternativel you can prop the existing wall and replace it in short sections.
Alternatively you can place narrow precast panels in front underpinning style and fill the gap between with no fines.

Other options could include using the building structure to laterally support the wall and underpinning under.

Hope Ive given you something useful.

 

[kieran1]

Thanks for your suggestions csd72.

The boundary is 1.0m behind the wall. Any driving of sheet piles would have to be done from the lower level. I forgot to mention this is an infill site between two neighbouring propreties. The existing retaining wall also runs behind these properties.

I'm concerned about underpinning or replacing the wall in sections. I guess I will have to wait for the geotech report.

Kieran

 

[InDepth]

Maybe you can jet grout behind the wall and essentially create a solid block behind the wall. I think braving the wall and filling in segments is a good idea (slot cut in 1m segments using an ABC method.)

 

[Patgeotech]

Maybe drill through the wall - install soil nails and apply thin coat of shotcrete with mesh reinforcement (temporary support). Then batter 45 degrees from base of existing wall to required excavation level. Build structure (use floor slabs to prop) and then remove sections of the battered sections - hopefully this makes some sense.