Sand or Solid Rock?

The city of Melbourne is famous for its Yarra River – ‘the river that runs upside-down.’ The Yarra is, for the most part, a pretty safe and healthy river. It just happens to carry a lot of silt, which gives it the appearance of being muddy. All that silt gets deposited at the mouth of the river, as it has done from time immemorial.

I remember years ago the authorities began to develop the Docklands area of Melbourne near the mouth of the Yarra for commercial and residential use.

The story goes that they drove huge piles into the ground to support the weight of the planned buildings. Piles are piers designed to go below loose soil onto something solid and immovable, thus enabling the structure above to stand strong.

Apparently, they drove 14m (45′) long piles into the silt, which promptly disappeared. They drove another on top, which also disappeared. I don’t recall how many had to be piled on top of the previous one before they found solid ground, but it was plenty.

The point is that silt can’t carry heavy loads. Unless they could get the load transferred to something solid below the silt, the structure above would collapse in short time.

Not unlike our Christian faith… Continue reading