Cunning Plan Number Three

Finally, some Earthquake-proofing. Floating Foundations

It seems to me that there are two main reasons for a house to become unliveable because of an earthquake.

·        The first is that the house was not designed to withstand an earthquake.

·        The second is that the ground beneath the house moves, ripping the house apart.

As a result, the cost to repair or replace a house affected by an earthquake can be astronomical. Multiply that by a city, and the insurance industry could be on its knees.

Solution:

If we can increase the earthquake strengthening regulations for new houses, then they will be able to withstand future earthquakes much better than they have recently.

How? Quite simply, start with the foundation.

Aren’t They Deep Enough?

It has been shown that homes with deep foundations, even very deep foundations, still succumb to a major earthquake. Actually, I believe that a deep foundation hinders rather than helps a house when it comes to surviving an earthquake.

When a deep foundation is sunk into the ground, it is like burying your fingers deep into the dirt, and taking great fistfuls of the ground. It does exactly what it is designed to do; holds on for dear life. Then, when the earth tries to move in two directions, the foundations stay where they are buried, and everything shears at the weakest point. The ground opens, and so does the house.

I saw a family on TV that moved from their broken home into their daughter’s playhouse. The reason why the playhouse remained intact was that, relative to its size, its floor was built to hold it’s shape and weight with or without support. You know the sort. The playhouse is built onto a pallet, or similar. It is delivered on the back of a truck, and rolled end over end to its final location. It's structure and integrity is unharmed by this transportation method.

By contrast, look at a house built on piles. If any piles sink or are pushed up, the floor distorts brutally, twisting doors and walls above. There is no cantilever ability in the house at all. It relies completely on every single pile staying exactly where it was put, and never moving even a millimetre.

Then there is the concrete floor. A thin ring of concrete around the building. As deep as you like, but  only a few inches thick, with a thin layer of concrete over a pile of shingle in the middle, the purpose of which is really only to stop moisture getting into your carpet.

When one of these floors breaks in an earthquake, the entire building is a write-off.

Cantilever Floor

My idea is to design the entire floor of the house like a cantilever, rather than a thin slab over a foundation. That may mean making it considerably thicker, and certainly involves reinforcing steel throughout the entire floor.

The next step is to tie the walls firmly to the floor, and to make them rigid. This stops the flexing that causes so much internal damage to a house. The result is that the house stays intact, like a cube, even under severe cantilever conditions. Then, when the earth tries to move in two directions, the floor stays undamaged, and the ground opens harmlessly beneath it. If the earth opens to the extent that it collapses under part of the house, the worst that can happen is that the house tips a little into the hole. It is undamaged, but on an angle. The solution is to jack up the house to level again, fill under it, and reconnect any pipes or services that have broken away. The house remains intact, because it does not flex or break. It simply moves as a single unit. It floats.

If a house is to be built on less stable land, a completely floating foundation may not always be practical. The solution could be to have additional anchors under the floating floor. To give stability in normal circumstances, foundation piles can be built into the corners of the floor, down into solid ground. Their point of connection with the cantilever floor should be designed as an intentional weak spot, weaker than the floor itself. In a strong enough earthquake, the floor can snap off the piles, to allow the house to float free and remain stable and intact, rather than succumb to the terminal deep foundation fate mentioned above.

While this Cantilever Floor design may add a few thousand to the building cost, it could save hundreds of thousands for the Insurance Company. We may almost be at the point where a new building will be uninsurable unless it complies with this type of earthquake-proofing design.