However, there are common faults that will certainly weaken the structure of a dry stone wall.
A really common mistake that those of you who ever built with lego will recognise! Basically a running joint should be avoided as it will always be a point of weakness where a bulge or hollow will form when the wall is under any sort of force and movement.
Spot the running joints almost from the top to the base of the wall
'Hearting' or Filler:
Often the things you can't see on a wall are the most important. A hollow wall, or a wall where the filler has just been thrown in will be weaker. The small stones that fill the gap between the two sides, give strength and flexibility to a wall. Where there is none, the wall will easily fall down, especially if any pressure is applied!
Kirk Ireton - A wall with no hearting; I pushed it over!
Carsington - another hollow wall...Once we took the copestones off it fell down!
Most people imagine that cement will strengthen a wall and in some circumstances it will. However, where the land around is liable to move, a well built dry stone wall will adapt, flex and settle to any movement. When a wall is cemented, it cannot do this, so it cracks and splits as the land settles.
Many animals, horses, sheep and cattle enjoy a good scratch on a wall and where there is a protruding sharp stone this will serve it's purpose well...until the wall falls down!
Yes, it does happen, unfortunately there are a number of poorly built walls which as you recognise what faults to look for you will start to see more and more!
Walls can be too narrow for their height, full of running joints, loose stones, soldiers (stones turned on their sides) large stones at the top rather than base of a wall, bulges, no or irregular batter (the angle of the sides) poor internal packing which is a major component of the wall's internal strength.