Can anyone tell me if a 200 year old dry stone retaining wall was built with underground foundations or not?
From what I gather these old walls don't have underground level foundations, but are built in such a way with through stones to stabilise the walls from movement or collapse.
It might have had rubble or boulder filled trench laid first before the actual wall was built ontop. But possibly nothing, just stones laid directly onto the bare clay
Dry stone walls are normally built with a batter, are thick and flexible, so a deep foundation isn't usually needed. Even house walls built back then often had very shallow footings, as the thick walls spread the load, and the lime mortar accommodated any movement.
Modern houses have deeper foundations because the thinner walls built in cement mortar don't allow for the same amount of settlement.
Thank you for your assistance. This is very helpful. This wall was measured at an exposed end section at the base. It measures approximately 2ft in depth.
If I am correct would this be the total thickness/width of the actual wall?
I am interested in knowing exactly how a dry stone retaining wall would have been constructed back in around the 1850s that's all
Any expert assistance would be appreciated.
The basic techniques haven't really changed. As mortar isn't used there hasn't even been a change from lime to cement.
Mortarless walls are still used as retaining walls nowadays, with a system like Allan blocks. They are laid on a gravel bed, and form a batter as they go up. Much easier than a dry stone wall. The advantage of a mortarless wall is that it allows moisture through. Hydrostatic pressure is a major cause of retaining wall failure.