Building behind retaining wall with no footing

[GeoPar]

I'm looking to build behind a retaining wall that has no footing but worried the whole lot could collapse. We will engage a structural engineer before the project goes to construction but we are just looking for some preliminary advise so it doesn't have to be redesigned post planning. I left a 2m gap between the existing and proposed as I assumed this would help the situation? I have read about a 45 degree rule from the proposed footing however, as you'll see, this would result in an extremely deep foundation. Any help / advise would be extremely appreciated!



Links to drawings
Section (please note the proposed will not be floating - I just am yet to design the foundation):

http://files.engineering.com/getfil...5cc&file=Highfield_Barn_DRAFT_section_NTS.pdf

Plan (the upper most grey wall is the retaining wall that has no footing):

http://files.engineering.com/getfil...6e22f2&file=Highfield_Barn_DRAFT_plan_NTS.pdf

Plan

 

[oldestguy]

I assume the grey wall is masonry or similar,perhaps stone mortared together. I also assume the new building will be paced lower than shown.

Unless some very unusual situation comes up it would appear that a nearby small building will have no important-effect on the existing barn wall.

 

[Ron]

Influence from new to old will depend a lot on existing soil conditions and loading. Get a geotech involved then a structural

 

[EireChch]

See attached. I roughly drew the Ka envelope for a phi of 30 degrees. Lowering the footing below the Ka envelope would not be excessively deep. If you were very concerned you could pile the downslope edge.

 

[GeoPar]

Many thanks all - I'm new to this forum but such a great response.

Oldestguy - Yes correct... and old stone masonry wall. No the new building is shown in the correct position - The new floor area has to tie in with the existing first floor level. Okay great - thanks for the advice.

Ron - Thanks for the advise. I will consult a Geotechnical when it comes to construction.

EireChch - We are planning do roughly what you have sketched out. I have enough information to press one with the planning drawings now and will consult relevant bodies when it comes to building regs / construction.

Thanks all.

 

[oldestguy]

Assuming the new building will have soil fill added in her area, there will be some added load against the barn wall. However, look at it this way. Stack a bunch of toy blocks one over the other and put some load on that stack of blocks (as a heavy stone wall) and see what it takes to push over the stack of blocks. For a heavy stone wall there is considerable natural resistance to having any noticeable effect from some earth loads against it.

Instead of the 30 degree limit of influence laterally,60 degrees is more common.