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Chapter 1
The weight of gravity: The physics of foundations
Inspecting a stone wall with Inari before carrying out repairs.
Dry-stacked stone wall in Co. Clare.
Between the ages of 12 and 17, I managed to break 13 bones in my teenage body, all on different occasions. This wasn’t a result of inept parenting but rather my own bumpy journey to discovering that no matter which way I rolled the dice, I could not win a wrestle with gravity. I now watch my ten-month-old daughter learning the same lesson, as she heaves herself from her back to sitting up, only to tip over sideways. Naturally, she finds this impossibly frustrating. My now healed bones echo with empathy for her, as the force of gravity is a relentless bully. Luckily for us, it is a predictable one.
Brickwork beneath plaster and paint, Australia.
We experience the pull of gravity in a similar way at any given location on Earth, towards the ground, or, more precisely, towards the centre of our planet. Understanding this natural phenomenon allows us to build impressively tall buildings with the confidence that they will stay up. When it comes to smaller, more humble structures, the same laws of physics apply. They also apply to the structure of our bodies. This is perhaps not so surprising, when you consider that we are all, on an atomic level, made up of the same stuff. All matter has a certain amount of gravitational pull, proportionate to its mass. The greater the mass, the greater the gravitational pull, which is why we are pulled towards the earth instead of being pulled towards each other. Although there are counter-forces at play, the planet, due to its sheer size, always wins.
Exercise
OUR BODIES AS BUILDINGS
Our bodies are probably the easiest place to understand the effects of gravity, so I want to encourage you to get active for a moment. Go outside and find some solid ground to stand on, whether it is grass, soil or sand. Stand with your feet together and try to feel the gravitational pull on your body. The mass of your body is being pulled towards the ground and your feet are providing the resistance. You can imagine that, without our wide, flat feet, our legs might penetrate straight into the ground, much like a cow’s hooves in mud. A smaller surface area provides less resistance to the force of gravity on your mass. It is no coincidence that in the language of construction, we refer to foundations as footings. Next, spread your legs shoulder-width apart to create an arch. This arch supports a tower, with two posts supported by two footings. While you are standing in this position, consider the elements of your body that are making this position possible. The combination of your rigid bones and elastic muscles are working together to resist the pull of gravity.
On a subconscious level, we are all aware of the unseen force of gravity. We instinctively make allowances for it, as well as placing great expectations on its presence. Right from the construction of our first prehistoric structures, architecture and engineering can be viewed as a response to the perpetual phenomenon of gravity and an answer to the question, How do we stack and combine materials in such a way to resist and redirect the force of gravity?
Ash forest at our home in Co. Clare, Ireland.
Centuries-old lime kiln in Co. Clare.
Massive earthen walls in New Mexico.
Foundations: redirecting the force of gravity
Now that we have a basic idea of the effects of gravity on our structures, we can look at the pivotal role of foundations. The average three-bedroom home weighs somewhere between 36 and 80 tonnes, which is the equivalent of 6 to 12 adult elephants, or 500–1000 people. Anyone who has been at a rainy music festival has seen what the weight of 1000 people can do to a landscape. The perpetual pull of gravity, which pushes the weight of our house down into the ground, requires an equal and opposite resistance to prevent it sinking down into the Earth’s surface.
In the past, before we had the skills and tools to create concrete, natural bedrock and rocky outcrops were sought after as solid foundations for society’s more substantial structures – castles, forts and towers. Even the Egyptian pyramids, which appear to be floating on a sandy sea, are in fact built on the huge layer of limestone bedrock that lies beneath the desert sands. Let’s use our body again to help us to understand why our ancestors decided to build on foundations of stone, as opposed to sand or earth. Imagine walking barefoot on a smooth, sandy beach. We can feel the ground compress beneath our feet as we walk, or even be pushed out to the sides and up between our toes. Compare this to the sensation of solid resistance when walking on stone or concrete, and we can start to understand the strong inclination to use solid foundations as a means of connecting the massive accumulative weight of ourselves, our buildings and their contents to the Earth.
Finding exposed stone was not always easy, and having the resources to dig down to the bedrock was not feasible for most, so the average medieval owner-builder had to be a little more creative in their methods. When digging down to undisturbed earth, which is earth that has not been tilled or broken apart in recent history, they found that the naturally compressed clay and sand was, in fact, stable enough to function as a base for the foundations of their homes. This undisturbed earth lies at different levels depending on where you are, but is most often found within a metre or two of the surface. Stones were used to fill the trench and raise the building up out of the ground.
Beautifully curved stone wall in Co. Clare.
Certain methods were more successful than others. The best results came from buildings where the stones were stacked in such a way that they would not shift or split under the load. And so we came to understand that the role of foundations was not only to connect us to solid ground, but to evenly disperse the weight of the building over as great an area as was necessary. Those medieval three-dimensional jigsaw masters had a clear, instinctual understanding of what is now known as the load path and how best to design for it. They discovered that if they stacked the stones in even layers, with overlapping joints, their heavy stone walls could not only be self-supporting, which was their primary function, but could also carry large amounts of additional weight. This method of making foundations was implemented for thousands of years, and fine-tuned as we spread across the land building structure after structure, digging down to undisturbed earth and building our way back up.
In areas on or near to water, it wasn’t quite so simple. Whether it is the ocean, a river or a marshland, the presence of water in soil makes it much more difficult to find solid ground. But necessity has always been the mother of invention, and being near a clean water source was also necessary for survival. And so we adapted again. Wooden post foundations have been found in Switzerland dating back as far back as 12,000 years ago. Driven into the soft earth of shallow lakes, these foundations kept the dwellings and the inhabitants out of reach of predatory animals and flooding. The same techniques were used to expand cities situated near, or on top of, the water sources they required to function, with the wooden posts needing constant repair as they deteriorated in the shallow waters. Experimenting with different types of wood, as well as the use of preservatives and treatments, continues into the present day. Since the 17th century, Boston city, Massachusetts has been expanding across its waterways, adding over 5000 square kilometres of man-made land atop deep-reaching f...
