Tuesday, October 15, 2013

Arch # 9

The Bridge Arch Retaining Wall

The basic 'arch shape' is very strong. A stone bridge can take a lot of weight because the arch is a fixed concave barrier to the downward pressure of gravity . Also, the stones in an arch are set on end, radiating slightly in such a way their strength and structure is maximized by their length relative to the direction of the forces coming down from above.

So then, why are there so few retaining wall applications utilizing this stronger 'concave' shape in the design. More importantly, why, in a wall that is supposed to hold back the horizontal force exerted by the ground behind it, are the stones laid flat? Shouldn't they be upright, standing on their ends the way they would if they were in an elongated bridge laid on its side?


  1. Very good question.

  2. I suppose it is because each stone settles more securely on the flat ,when they are on end you have to support them from the side.

  3. A bridge arch is curved, which does not always correspond to the required shape of a retaining wall. The weight of the bridge arch itself helps strengthen the structure. That cannot happen when the structure is lying on its side.
    Also what takes the place of the abutments - another element of the bridge which reacts against the pressure from the arch?

  4. The stone dam at Jones Falls (Ontario, Canada) was an amazing feat of engineering in 1826 when Col By tricked the Rideau Canal to flow both ways. Build of massive sandstone blocks laid in upright voussoir position and arched against the force of the flooded lake and clay lining above, it is a place that all stonemasons must visit.