Waterjetting 19c - Of soil removal by water

The tragedy in Washington state, where a hillside slid down, across a river and destroyed and covered the small community of Oso on the other side is a reminder of the ways in which natural ground saturation can help dislodge large volumes of material. While it is unlikely that the exact trigger for the slide will be identified the underlying cause is well known. As water from the heavy persistent rains permeated down through the hillside it penetrated deeply into the sand, silt and clays that made up the cliff, filling the voids in the material and reducing the friction that held the slope together.

Once the water is between the grains there is a second stage, where the overlying water adds hydrostatic pressure to the water below it. This pressure starts to push the grains apart, further reducing the friction holding the grains together and, since water has no shear resistance, lowering the overall resistance to the gravity that is pulling the overlying material down a potential failure plane. Once the resistance falls below that pull the slope starts to fail. It happens very quickly and large volumes can move almost as fast as though it were just water. In this case the water moved roughly 15 million cubic yards of material off the mountain. and across the valley.

The power of water to move material once dislodged was an early part of the mining process, and an earlier post referred to “hushing” where water was first trapped, and then released to erode away overlying soil, and then ore, before carrying it down to a flume where the valuable mineral could be trapped and recovered. But it does not take much pressure to dislodge weak material. Russian studies* have shown that light soil can be moved with a pressure of only about 10 psi (which would be generated in the water at the bottom of a slope only 20-ft high), while medium soil would require perhaps 30 psi, and firm clay would need a pressure of about 100 psi before the jet would mine and erode it.

That ability to move soil using a monitor was further developed in Russia, where tests showed that it would take water flows of between 3 and 10 times the amount of soil being removed depending on the strength of the material. In the gold mining regions around Lake Bykal it lowered mining costs to 40% of that for conventional mining, and gradually the tool found wider application in general soil removal, being used in the construction of several dams, and also for soil removal during construction of the Moscow Canal.

An interesting example of the speed and effectiveness with which waterjets can remove relatively soft soil formations arose during the Yom Kippur War (10th of Ramadan War, October 1973) between Egypt and Israel. The Israeli Army had built defensive positions along the edge of the Suez Canal and these were mounted behind an earthen and sand barrier known as the Bar-Lev line.

Egyptian intelligence had determined** that the Israeli Army had assumed it would take 24 hours for this barrier to be breached, and a total of 48 hours for the Egyptian tank forces to successfully penetrate the line. The response time of the military units was planned accordingly. This time estimate was based upon the time that it was expected to take to make a hole 22-ft wide through the barrier, since this had, for each breech, to move 60 cu yards of material, and a total of 60 such holes were needed to get enough troops through to be effective. Conventional methods involving explosives, artillery, and bulldozers would taken over ten to twelve hours, and required nearly ideal working conditions. For example, sixty men, 600 pounds of explosives, and one bulldozer would have needed five to six hours, uninterrupted by Israeli fire, to clear 2,000 cubic yards of largely sand from the wall. Employing a bulldozer on the east bank while protecting the congested landing site from Israeli artillery would be nearly impossible during the initial hours of the assault phase. Construction of much-needed bridges for the main army would consequently begin much too late.

Figure 1. Using waterjets to breech the Bar-Lev line during the 1973 war (Mashpedia)

To deal with these 70-ft high sand and earth barriers, the Egyptians instead used water cannons fashioned from hoses attached to dredging pumps that were floated on platforms in the canal. A study was made of the speed with which different pumps could move the sand:soil mix and the initial tests with British pumps showed that it would take around 3 hours. But by combining them with larger German pumps into six pumps per breech the army was able to get the time down to about two hours, although it took a little time after that to deal with the residual mud on the floor of the breech and give an adequate road for the tanks and other vehicles. A total of 81 holes were made, moving over 3 million cubic yards of material.

Figure 2. Egyptian forces crossing the Suez Canal, showing the size of the breech created (Wikipedia)

The bridges were then put in place, and the Egyptian Army moved on into the Sinai, well ahead of the time that they had been anticipated to be there.

The combination of high-pressure water to dislodge and separate the particles of a soil/sand layer can be combined with the active suction from a modern vacuum truck, in what is now being called hydro-excavation. By removing the soil and water as the excavation is made this stops water from entering the walls of the excavation and leaves them relatively dry – thus resolving one of the problems that the Egyptian army encountered after their holes had been made. At the same time, by using smaller jets at higher pressures and moving them much faster the excavation rates can also be increased, with lower water volumes, so that narrow trenches can be excavated without the need for support, where rapid access is needed. But I will talk about those applications in a separate post.

*Okrimenko, V.A., "Hydro-Monitor Operator in Coal Mines and Pits", State Scientific Technical Press of Literature on Mining, Moscow, 1962, pp. 264 (Translation U.S. Army Foreign Science and Technology Center, Document AD 820634, 1967).
**London Sunday Times, December 16, 1973, p. 33

The gift of coal

I was given a bar of ChoCOALate in my stocking this Christmas. Much amusement was had by all. But the growing dependence of the world on coal, is beginning to get a recognition that has been more evident in the denial of it’s long-term role as a base fuel for the last couple of years. And so, in leading up to a pleasant meaning which exists for a gift of coal let me chat a bit more about coal’s future.

Just this past week George Will noted that Cowlitz County in Washington had approved a coal terminal that would allow the shipping of coal from the United States to China. About 5 million tons a year of coal would be moved by train to Longview from either Montana or Wyoming, and then be exported.

So it's a major new development for the region to begin with. And they are talking about a significant amount of coal – more than 5 million tons a year to start with, which is about twice what the Boardman coal-fired power plant burns in a year. And opponents suspect that number could grow.

But I think the biggest attention-getter is what's driving this proposal, which is growing demand for energy in China and other growing Asian countries.

It is anticipated that coal will start to move through the terminal by the end of 2011. However the environmental concerns have already led the State Department of Ecology to become involved, noting:

In October 2010, Ecology suggested Cowlitz County officials expand their greenhouse gas emissions analysis more broadly in their environmental review. The final review did provide additional evaluation, but Ecology believes it did not go far enough in considering greenhouse gas emissions outside the immediate boundaries of the project.

Yet disallowing the terminal will have little if any impact on the Chinese use of coal. Coal is already being exported through Vancouver in Canada, to the tune of some 26 million tons a year. China is increasing the amount that it imports. By selling into that Asian market Australia was able to avoid the recent recession that hit most of the rest of the world, and while it exports coal to China, Japan and India, it is the growth in Chinese orders that have caught attention recently.

And that demand will not diminish in the reasonable future, despite those who cite the Patzek paper on coal’s imminent decline. For, as even “The Atlantic” magazine noted this past month, in talking about clean coal:

But two ideas that underlie the term are taken with complete seriousness by businesses, scientists, and government officials in China and America, and are the basis of the most extensive cooperation now under way between the countries on climate issues. One is that coal can be used in less damaging, more sustainable ways than it is now. The other is that it must be used in those ways, because there is no plausible other way to meet what will be, absent an economic or social cataclysm, the world’s unavoidable energy demands.

For as the article points out

The journalist Robert Bryce (ed - in the book Power Hungry) has drawn on U.S. government figures to show that between 1995 and 2008, “the absolute increase in total electricity produced by coal was about 5.8 times as great as the increase from wind and 823 times as great as the increase from solar”—and this during the dawn of the green-energy era in America. Power generated by the wind and sun increased significantly in America last year; but power generated by coal increased more than seven times as much. . . . . .(he) describes a visit to a single coal mine, the Cardinal Mine in western Kentucky, whose daily output supports three-quarters as much electricity generation as all the solar and wind facilities in the United States combined.

And in China it takes about 21 months to install a new coal-fired power plant. To supply those power stations they are seeking additional suppliers of coal from around the world.

Arch Coal has just bought the lease to 587 million tons of coal in the Otter Creek reserve in Montana. The company already owned rights to 731 million tons , and it is suggested that the deposits will be mined at the rate of around 22 million tons a year, although mining may not begin for five years.

In the meanwhile, even if the folks in Washington don’t want the terminal, CN would be happy to ship it through terminals at Vancouver and Prince Rupert. Trains take 45 hours from the mines in BC to Ridley at Prince Rupert, and 70 hours to Vancouver, while they take 55 hours from Alberta. It then takes 2 weeks for the ships to get to Tianjin, Shanghai, Quingdao, Guangzhou or Hong Kong. (Give or take a day, and assuming an average speed of 13.5 knots).


Getting coal out of Montana would require improved rail linkages, but one 35-mile link has already been installed to allow the Signal Peak Mine to be developed in the short term, raising Montana production from the 45 million tons produced in 2008. Plans to increase Montana production include a new line known as the Tongue River Railroad which would connect into the Miles City BNSF line that goes up to Glendive, whence it could easily move on into Canada, if it could not move west to Washington.

Planned Railroad relative to mine development

It has taken since 1983 to get planning for the railroad extension this far. And it is still being protested.

Even without the Montana production and even if the Australian mine production is constrained by transient floods, there are lots of other sources that the Chinese could use. These include Mozambique, where plans are moving ahead to increase local mine production up to 20 million tons a year from an estimated 9 billion ton deposit. There are both Chinese and Indian investors in this project, which will occur as the Minas Moatize mine also expands production up to 11 mt/year. Mine development will require improved railroad and port facilities, but it is likely that these can be implemented more rapidly in Africa than they can, presently, in the United States.

The point of which is that there are many places that China and Asia can purchase coal from. There are several places along the Western seaboard from which American coal can be shipped, and large deposits that can be mined to supply that coal. It may even come from those resources that are, in “peer reviewed” papers, considered to be insignificant. But it will get to China, and it will be used to sustain and grow that economy.

With which thought I wish you all a Happy New Year. In my youth the first to come through the door after midnight was to bring in some shortbread or black bun, a couple of pennies, and a piece of coal – and the “first foot” was then rewarded with a tot of, what we called “tea without milk or sugar.” (Good Scottish whisky). The coal was for a wish of enough fuel to keep you warm and fed through the year, the shortbread/black bun represented that food, and the money was for prosperity. Virtually therefore, let me offer you those gifts for this year, and for the years to come.