Retaining capability of regular 2-skin block wall. And how does concrete behave?

[Stu84]

Morning all.  Looking for some engineering consideration.  Please see images.  Here we go!

 

The exposed face of the small car park is, at its tallest, 530mm measured from the foundation.  It gradually slopes to less.  The total wall thickness is 340mm: block-infill-block.  

 

It's standard practice to infill wall cavity with a weak concrete mix. However the maximum I can fill to is 320mm (above foundation).  As otherwise I start to get close to  internal skin DPC level.

 

Occasional car traffic uses this small car park. And a few times a year you'll see a heavy lorry reversing down to drop something off.

 

The foundation projects about 120mm from the outer skin.  S.E. has suggested that filling this void between the outer skin and the excavated edge with concrete will protect the cavity wall from collapsing.

 

This solution is not ideal as the external concrete will then be higher than the infill so would water in the cavity have trouble trying to escape?  Secondly I struggle to understand how filling the external void with concrete will help prevent the cavity wall from collapsing inwards?  Won't a vehicle parked on the tarmac close to the concrete cause a horizontal component of force which would be transmitted through to the block wall via the concrete? 

 

My suggestion was to epoxy a few vertical T12 rebar rods in a line, maybe 3 across a metre, and slide a metal stainless steel panel between the rebar and the edge as an additional retainer. I wouldn't need to do the entire length, just the highest point, so a metre should do.  I'd then back fill with soil/MOT Type 1 and tarmac. 

 

Thanks all!

 

Stu

 

[Stu84]

To update on this.  I sought a second opinion from another engineer.

 

He confirmed that the surcharge load (soil + lorry etc) would result in a lateral pressure against the external wall. 

 

He designed a solution based on 10kN lateral pressure.  This involved a line of vertical rebars with horizontals to be placed between the outer skin and the excavated face and also another line of verticals with horizontals placed centrally within the cavity.  All rebar to be surrounded by 50mm of C25 concrete (75mm cover against the excavated face).  He applied partial factors for safety.

 

Building inspector notified and happy.

 

Thanks