Tower Bridge (Part 1)
From the bottom up! It's not a joke. When you look at Tower Bridge, you see a magnificent structure, but did you know that more of the bridge is below the water than above the water?
You start with the foundation. And in the case of Tower Bridge, you start deep, deep, deep under the surface of the Thames - 10 metres below the surface of the water, in fact.
On 22nd April 1886, divers started preparing the riverbed for the massive piers. It must have been a scary job - after all, it was 1886. They didn't have scuba gear and safety devices and computer equipment. The divers wore leather suits with metal helmets, and they were connected to the surface by air tubes. They used hand tools and shovels.
Above them, on barges, other workers built caissons. What is a caisson? I'm glad you asked.
A caisson is an open-ended watertight metal box, with sharp edges.
Workers lowered each caisson into the river - down, down, down - until it rested on the riverbed. While the sharp edge of the caisson dug into the riverbed, the workers forced them deep into the soil. They sunk the caissons to 9 metres deep, into watertight London clay. The London clay would support the enormous weight of Tower Bridge!
Twenty-four caissons (12 in each pier) were constructed, and when they were complete, they were filled with concrete. The workers left space within each pier for steel pillars (which would support the towers), and for the bascule machinery.
It took four years to construct the piers!
To learn more about HOW they built Tower Bridge, you'll have to read the next blog! But that's all for now.