Stage 2: Foundation

Every building starts with a foundation. With the frost depth in Nakatombetsu at up to 90cm, our foundation was going to have to start deep. However, the water table is also shallow here. So, to compensate, we began the foundation at 50cm below ground level and then made up for the remaining depth by berming the structure another 50cm.

After marking and leveling our site, we began the excavation.

Marking and Leveling

Once the excavation was the proper breadth and depth, we set about making it level. For this, we ditched the backhoe and worked by hand with shovels and tampers.

Leveling the Excavation

Next, we hand-dug a trench along the outer cirumference for the installation of a foundational drain pipe. Nakatombetsu gets a lot of rainfall and we don’t want to take any chances with an earthen structure. Trench dimensions were approximately 30cm wide and ranged from 20cm to 30cm below the level of excavation (to create a slope for proper drainage) .

Digging the Drainpipe Trench

A trench was excavated with the backhoe to create a path for which to connect the foundational drain pipe to the municipal drain pipe running nearby (very convenient).

Trench to Municipal Drain

To connect to the municipal drain, we had to use a PIC drill and bore a hole through the concrete of an access compartment.

The pipe was installed and fitted into the municipal drain. The access hole was then resealed with fresh concrete.

Installed Drain Pipe

Connection to the Municipal DrainResealing the Installation Hole

Once the concrete was dry, the foundation was infilled (in its entirety) with 10cm of gravel. This was again hand tamped. The trench to the municipal drain was simply back-filled and tamped with the back-hoe.

Infilling Excavation with 10cm Gravel

Next we installed a compass at the center of the foundation. We used scaffolding piping that a friend had laying around. However, as long as the compass is secure and level, any number of options could be made to work. First, a vertical pipe was driven down about a meter in depth. A piece of plywood was secured around the pipe at the surface of the foundation to prevent the pipe from sinking with use. A vertical arm extension was attached, upon which a vertically pivoting horizontal arm was attached. Both the vertical and horizontal arms were measured and marked at 10cm increments. Bubble levels were also attached to make it easy to quickly check the entire circumference during construction. (Note: second picture shows us creating the platform around the circumference upon which the first bags will be laid)

Installing and Marking Center PoleHorizontal Radial Arm with Bubble Level

As an extra precaution against sinkage, meter long 4cm diameter stakes were driven into the foundation around the cirumference were the first bags would lay. Then two strands of 0.5mm wire wrapped around the stake heads. The heads were not perfectly flush with the gravel, but they were close enough to lay bags, as the bags are soft when first laid and can easily conform to surface irregularities.

Installing foundation stakes prep

Installing Foundation Support Stakes

Installing foundation stakes wire prep

Using the horizontal arm of our compass and a can of spray paint, we marked the inner circumference of our wall. From there, we were ready to lay the first layer of bags in our stem wall.


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