Phase I – Stone Retaining Wall – Westford, MA

The first phase of this project was to clear the hillside and rebuild the retaining wall.  As discussed briefly in the project overview, the original stone wall had been built poorly.  The builder dry laid the fieldstone directly on the clay subsoil, carefully faced the wall without giving much attention to structural integrity, and then mortared the top course to achieve a clean cap.  This method was neither here nor there.  A properly built dry wall can be laid right on the ground.  If the stones are stacked for strength and tied back into the wall, the stones will settle with ground movement but remain structurally sound.  And if the wall doesn’t have a perfectly clean face and cap to begin with, visually the movement will go unnoticed.

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original stone retaining wall

If the finer finish is desired, however, the builder should have laid a sturdy base for the wall to minimize ground movement and then mortared the entire wall so that it was one rigid mass.  In this way the wall resists ground movement and other forces.  This method takes more preparation but is an easier way to produce a finer finish.  The downside is that when/if the forces become to great for the wall to withstand, the mortar will crack and the effect will be very noticeable and difficult to repair.

Fortunately since most of the wall was dry laid, the stones were still clean and we were able to reuse them to build the wall.  Our plan was to tear out the entire wall, lay a gravel base, and dry lay the stones with a focus on structural integrity.   The gravel base serves a couple purposes in this case.  First it provides drainage for the wall.  It lets water drain down away from the wall stones, and if any freezing occurs there is plenty of flexibility and air space in the gravel to take up the movement.  In this case the gravel base also provided a drainage channel for the whole hillside.  As water runs off the hillside, it will settle in the low channel beneath the wall.  And being that our channel was sloped towards the lower end of the property, the water will gather and flow down and out to serve as part of our drainage system.

Here we have cleared the hillside of the larger trees and brush.  It’s a nice looking wall, but sadly it’s been undermined in too many places and has to come down.

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original hillside + wall

Here we are clearing the rest of the hillside with the machine.  The wall stood up to it’s weight for a little while and then…

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hillside clearing

The stone wall collapses and we dig out the rest of it:

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the wall collapses

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excavating the wall

The wall is fully excavated.  As it turns it was laid over 4′ thick.  That’s a lot of stone to deal with, but, it turns out to be quite useful for the rest of the project.

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excavated wall

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100-150 tons of stone

After the wall is excavated our suspicions are confirmed that the subsoil is in face almost solid clay.  Clay does not let water percolate, and when it saturates it stays wet for a long time.  With some well timed rain, our trench fills with water and we get a good look at what’s been going on behind the old wall.

With the trench sloping downhill, we fill the gravel base, and then lay the base course of wall stone.  The wall now has a solid base to sit on, and there is a drainage channel below it to send runoff down hill and away from the front yard:

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gravel base

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base course of wallstone

Now the rest of the wall can go together.  We lay the stones stack style so that the stones extend back into the wall and only the small face shows.  The machine helps with the larger stones and much of it is done by hand.  After a week or so of hard work the wall is coming together:

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rebuilding the retaining wall

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rebuilding the stone wall

The wall is for the most part complete.  There is some extra stone that we will be able to use for the next portion of the project.   The next portion being a dry stream bed that will pick up the water flow at the end of the wall and carry it down and around the side of the property.

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fieldstone retaining wall – Westford, MA

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fieldstone retaining wall, Westford, MA