UK - 1862 floods damage railway tunnel

[John Ashworth]

From the archive: Floods damage Metropolitan Railway tunnel, 20 June 1862

* The Guardian, Saturday 20 June 2009
* Article history

Since the sinking of the Fleet ditch between Ray Street and Saffron Hill, great fears have been entertained by the contractors for the safety of the Metropolitan Railway tunnel and brick arching in that district. From Clerkenwell Workhouse along Victoria Street the tunnel and arches run parallel with the Fleet sewer, created about seven years since. These fears have been fatally verified. The heavy rains of Sunday last have caused an immense accumulation of water in the sewers, which gradually found its way into the tunnel. At an early hour on Wednesday morning, it was discovered that there was about twelve feet of water in the tunnel, which was forcing its way through the sides of the brickwork. The bricklayers were at once ordered to desist from work, and a number of men were lowered into the tunnel in baskets, with the object of breaking holes in the sides of the tunnel to allow the water to escape.

After this operation had been going on for some time, some portions of the foundations of the arches were observed to be giving way, and the men were at once hauled up from their dangerous post. Scarcely had the last man reached the surface than the whole mass of brickwork and timber appeared to be bodily lifted up in the air, and fell into one heap of ruins. Several hundred yards of tunnelling and arches were totally destroyed, while the water was flooding the ruins in all directions.

The scene presented the appearance of a destructive earthquake. The water came pouring down from the high level in torrents, flooding that portion of the tunnel still remaining standing, destroying the gas-mains in Ray Street, inundating the cellars of houses, and appearing to have uncontrolled power over the whole portion of that low-lying district. The destruction of property is very great, and t accident will cause a delay of three months in the opening of the railway.

During the night, great quantities of earth, brickwork, and timber were constantly falling. Immediately on the spot where the accident has taken place was situated the burial ground of St. Peter's, which was removed consequent upon the making of the new street. The bodies then remaining in the ground were collected and placed in a mausoleum, erected on the spot, in an excavation purposely made. On Wednesday night this building was struck by the falling timbers of the railway, and the upper portions of the walls shattered to pieces, while the lower part was flooded by water, and many of the bodies were washed out into the open excavation, presenting a most sickening sight.

[Steve Appleton]

This is apparently a real problem with brick arches. Two evenings ago I watched a disaster program in which several upmarket houses suddenly collapsed (literally toppled) into a massive sink-hole and washaway in a Los Angeles suburb in the middle of the night, the result of an outward ballooning and collapse of an old Victorian brick-arch sewer/drain that had become pressurised by excessive rain-water whilst the surrounding sandy soil had become waterlogged and liquified.
Brick arches gain their immense strength from the weight (counter-force) of the surrounding environment (masonry or soil) resisting any outward (radial) forces that may exist, whilst forcing the arch to vector all the radial forces ultimately vertically into the supporting columns or foundations. Brick and masonry arches can support enormous circumfrential and radial forces directed inward but, unlike steel (which works well in tension), masonry arches cannot support any nett outward radial forces at all. Remove or reduce the inward radial forces that surround the arch and you have a recipe for disaster.