I've recently dug out some patio slabs which were laid behind my front garden wall (wall is around 3ft high). I've also taken out the cement which was used to fill the gap between the slabs and the wall - resulting in one or two lumps of rock/stones coming with it. Although not very deep I'm a little worried this may be part of the foundations for the wall.
The wall still seems stable but how would I go about ensuring the foundations are good? Or is this necessary?
Doesn't sound necessary to me. You might want to dig a small hole down to
18" or so and find the 'real' foundation strip of the wall, for peace of mind.
Or even easier, use an SDS drill with a long bit and drill down alongside the wall until you feel the drill bit hit softer material. Mark the drill and measure, should give you a reasonably good idea of how deep the wall foundation actually is without any need to dig.
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