Traditional or engineered building technique? Lessons for the traditional way of building drystone walls.

As drystone masons we build our walls most of the time in the traditional way (Fig A ). It is only when we have to build retaining walls supporting a road or a building that the wall dimensions must be calculated by an engineer. In the traditional building technique the outer face of the drystone masonry is clearly distinguished from the backfilling. There is also no trapezoidal cross-section (Fig A ). In the engineered building technique a trapezoidal cross section is calculated which must be filled by the dry stone mason in consistent stone quality (Fig B) (In practice, it has been proven that in addition to the team building the wall, another team presorts and prepares the stone material. The effort required to build such a retaining wall is therefore much greater than with traditional dry stone masonry). 

While in the engineered building technique, the bearing capacity of the masonry can be calculated precisely, this is not the case in the traditional building technique. Still the traditional building technique does its duty without any problems in many places. The load-bearing behaviour of such walls can be understood as follows:

The traditional dry stone wall forms a kind of trapezoidal cross-section in the area of the long trough stones, if the backing stones are carefully placed in this area. Care must be taken to ensure that the longest trough stones are placed at the bottom and that their length then decreases towards the top  ( Fig C). If this rule is not observed, the result will be an irregular cross-section with reduced load-bearing capacity ( Fig B).