I have been puzzling over what this object is for. I think it must be inserted in a trench to stop the sides collapsing on workers tightening these blue bolts.

As I grow older I find myself more inclined to start sentences - nay, paragraphs - with 'as I grow older'. I also become more impressed by the amount of planning and organisation which goes unseen in making our complex society function. Bertrand Russell defined civilisation in terms of forethought and knowledge. At one time he even suggested a way of measuring it:

"That is to say, the forethought is obtained by dividing the present pain by the future pleasure and then multiplying by the interval of time between them."

I conclude that civil engineers are very civilised people.