Gravel Trench Footing Construction

Earlier this week we started filling the trenches with gravel. A gravel trench foundation, also known as a rubble trench or french drain, is an alternative foundation that requires an engineer’s seal to be approved in the state of New Mexico.

The trenches are lined with filter fabric to reduce the amount of mud that gets washed into the gravel. We have installed 2″ rigid foam insulation to a depth of 2 feet on the inside wall of the trenches. We are using 3/4″ gravel to fill the trench. We are also setting a 4″ diameter perforated PVC pipe at a slope of an 1/8″ per linear foot in the gravel for drainage of any water that may find its way into the footing.

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Megan and Daniel adding gravel to the trench to secure the drain pipe. All the elements of the gravel trench can be seen in this photo: rigid foam insulation, filter fabric, gravel and drain pipe
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Another photo showing the elements of the gravel trench foundation (note that the holes of the drain pipe are on the underside of the pipe and are not visible)

Getting the slope right on the drain pipe has been a time-consuming process for us. The pipe comes in 10′ lengths, so we make sure to achieve the right slope for every 10′ section. However, when we double-checked the slope of the pipe after laying our first 80 feet, we realized that somehow the slope had gotten off and we had to correct it. It now seems pretty essential to really pack in gravel on the sides of each 10′ section once you have the slope you want, so that the pipe doesn’t lift up as you connect additional pipe lengths. We are definitely learning as we go!

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We are using a transit level to measure the slope of the pipe as we lay each section

2 thoughts on “Gravel Trench Footing Construction

  1. Incredible! It pays to be perfectionists, no doubt, on a job like this. Smart to course-correct as you go along. Your pictures and words are wonderful. What’s your timeframe?

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    1. Thanks Lolly! Time frames are tricky things. I’ve had to accept that it’s really hard to predict how long various construction steps will take. I’m trying to accept the pace that things are going and be happy with our progress. Thanks for reading and check back in with us soon!

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