Trial hole - Bottom of foundations?

[Tentontousand]

So I started digging down the side of my single storey extension to see how deep the foundations are, as we'd like to build on top but I've seem to have come to this point already at around 550mm down. Is that narrow solid strip at the bottom the end of the foundations? It doesn't seem very deep down. I believe this extension was build in the late 70s by god knows who.

 

[KenGMac]

What you may have uncovered is the foundation?

The founds are in effect an inverted "T" so the "narrow solid strip" you mention and show in your image will probably mean that the foundation continues downward for a further depth, could be 100.mm to Who knows.

Suggest more excavation, as you have done but down the side of the "narrow solid strip"

In general terms, founds should be wider at the bottom of the excavation, this to assist in spreading the imposed load, the spread of the founds should depend on ground conditions.

Ken.

 

[noseall]

Not sure what I'm looking at there as there are no definitive indicators of jointed masonry. It looks like the edge of some thick concrete (raft?) plus some block-work at the bottom. Too confusing to say.