Thursday, March 13, 2014

Waterjetting 19a - a little history

A small personal introduction – some fifty-odd years ago I was about to graduate with a BSc degree from the University of Leeds and was then offered the option of going on for a doctorate. Since this was a Mining Department they had a number of different options that I could have followed, but I discussed this with my father, who was responsible for mechanization of one of the National Coal Board areas, and chose to study the development of high-pressure waterjets as it applied to mining.

The technology was in an extremely early stage of its development at the time in the West, although as I rapidly learned, there were already major uses for the technology in what was then the USSR. And so, with a laboratory that contained a small Uraca 9,500 psi, 4 gpm pump, I began a study that led to a lifetime career.

Some of the early things that I learned came to be adopted throughout the industry, and some of the lessons quietly disappeared. But I thought it would be interesting to go back to some of that work, particularly tying in the work done around the world in the cutting of coal and rock, so that some of these lessons could become clearer, remembered and passed on.

I was fortunate that Leeds was close to the National Lending Library at Boston Spa, and thus we came to an agreement that should I need any of the foreign papers (particularly those in Russian) not otherwise available, that they would machine translate these for me, and then we would put them into technical English. (Not nearly as easy as it sounds since computational power was relatively at about the level of an abacus relative to the standards of today).

In the beginning we were much more focused on the work that the Russians had carried out in cutting rock, although once I came to Rolla that relatively rapidly switched over into studying the work done on the mining of coal. However it may make the story more easy to follow if I begin with a return to the beginning and then work through the use in coal mining and follow that through into rock cutting.

Just after I began this series I wrote about the early work in what is now the country of Georgia where the native inhabitants were collecting gold in flumes lined with sheepskins that they hung in trees to dry – only to have a bunch of Greek thieves led by some guy called Jason, come along and steal them. They had used the natural force of streams to erode away the valuable ore deposits and carry the debris down streams and into the flumes. This idea was then developed by the Romans. After weakening and breaking gold ore in Spain through fire and gravitational collapse, they used a diverted stream to carry the broken ore out into flumes, where again the gold could be captured.

It has been said that after the Fall of Rome and the following Dark Ages that it took the world over a thousand years to get back to the technological levels that the Romans had achieved (the example of concrete is often used). In a sense this is also true of what is now known as hydraulic mining, since the practice largely fell off the scene until the use of Hushing was resurrected in the UK. The technique involves storing water behind a dam and then rapidly releasing it in a torrent to wash out and carry ore and overlying cover away down into prepared flumes. The area around such mines (found in the Yorkshire dales) is characterized by the deep channels cut into the ground by the water flow.

Figure 1. The region above the mine at Bunton in Swaledale, where hushing was used to expose and erode the mineral veins. (My Learning )

These mines date back to the early 1800’s while earlier reported work in Cornwall (based on the use in the North) in about 1500 was not apparently as successful and led to some loss of life. But that reference does indicate that the practice was already in use in Yorkshire, although there are few records to describe it before the citation above.

And so the first lesson to learn is that, if you hit a body (in this case rock and the overlying soil) with enough total force and water volume, that the target will erode and be carried away by the water flow. This is something that is evident whenever there is a severe storm along a coast around the world. See, for example, the following sequence of photos of the coastal highway near Ocean Beach CA in 2010.

Figure 2. Wave erosion of the highway near San Francisco (USGS )

In this case the shoreline was eaten back a distance of some 184 feet. And each winter we are shown the evidence of waves eating away at the foundations of houses built too close to an eroding cliff wall.

Yet it was not until the gold-rush days in California following the discovery at Sutters Mill on the American River in 1848, that large-scale water volumes were first used for the removal of not only the soil overlying the gold, but also the removal and disintegration of the gold-bearing sandstone beneath. And that is the story that I will tell next time. Although I will close with a description form that time of Sutter's Fort.
Ten miles from the river we passed Sutters fort, an old looking heap of buildings surrounded by an high wall of unburnt brick, & situated in the midst of a pleasant fertile plain, covered with grass and a few scattering oaks, with numerous tame cattle & mules. We walked by the wagon & at night cooked our suppers, rolled our blankets around us & lay down to rest on the ground, with nothing but the broad canopy of the heavens over us & slept soundly without fear or molestation.
For those not in the know Sutters Fort is to be found in the heart of downtown Sacramento.

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