A Water Channel… Some Rubble… A Foundation!

 

 

Rainwater washes underground and tends to seep upwards through the foundation and into the house.

What if the foundation itself were water permeable? A rubble trench foundation is a trench filled and compacted with dry rubble, with a water channel at the bottom. Rainwater flows through the rubble, into the channel and is taken out of the foundation by slope.

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Digging of the trench for foundation. Trench width = 460mm. The depth was varied and the bottom given a slope of 1” for every 4’ (1:50).

The site was first cleared of vegetation and stones. The topsoil and subsoil are always piled separately. Topsoil, being rich in humus, will be used for gardens later, while subsoil can be used for construction, i.e., in mortar, cob, earthcrete, etc.

Instead of making a site plan drawing and then setting it out on the site, an L-shape layout was formed at 1:1 scale using people to try various orientation options. Further, steel pegs, sticks and stones were used to mark the trench.

In order to allow the water to flow along the foundation bottom, it needs to be sloped sufficiently and in a specific direction. The trench was dug till a depth of 1’6” at the highest point and 3’ at the lowest, providing a drop of 1” for every 4’ (approximately 1:50 slope).

 

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The bottom of the trench was laid with granite stones forming a water channel. Long stones laid on their narrow sides, with a gap of 4” define the side walls of the channel. Large flat stones laid on these side walls take the load of the rubble above. The water channel was then tested for stability by walking on it barefoot. Rocky stones were balanced using smaller flat stones kept under them.

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Rubble collected from demolition waste was filled on either side of the channel and compacted to keep the channel from collapsing. Any rubble that has no aesthetic value can be used for the foundation as it is, ultimately, not visible. The same rubble was filled till about 10cm below the ground level, and compacted using hammers. Granite and red sandstone were spared to be used for the plinth later.

The lowest level of the water channel occurs at a point where it joins an existing water channel, which leads out of the site.

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