Waterjetting 35d - More video on hydro-excavation

In the evolution of the design of a waterjet/suction tool described in the last post I commented on the ability to balance the jets so that they did not spray material beyond the suction shroud. At the same time the shroud, to be most effective, has to be within a quarter–of-an-inch of the final surface, which means that the jets have to cut clearance for the head as it moves. Bearing in mind that the head will be manipulated around the excavation, this means that clearance has to be maintained on all sides.

Figure 1. Pass of a cleaning head over a 2-inch sand layer sitting on a set of concrete blocks that are not confined. The video shows the removal of the sand, without water escape.

I apologize for the quality of the tape, but these were research records that we were making of the experiments, merely to get certain data from them and they were not intended for transmission when made.

The second point I wanted to include was that of the ability to use the same design to cut a trench in harder material, again without the spreading of water beyond the trench. The material is a relatively weak cement.

Figure 2. Four passes over a weak cement to show that all the material removed can be aspirated at the time of excavation.

The tapes show how one can cut trenches in either soil or light rock fairly quickly and without making much disturbance outside the slot. Obviously the material removed can be collected in a vacuum truck and poured back into the trench after the trench work is complete.

In a later post I will show how this can also be used as part of a tool we developed to find, expose and then neutralize landmines.

Waterjetting 35c - Developing a waste removal shroud - video.

The short videotapes in this segment show the evolution of a combination of a waterjet and a suction line as a way of easily removing soil or sand relatively quickly. It is a subject covered in an earlier post. These video clips show some of the tests that helped us to develop that design.

As mentioned in that earlier post the central tube connects to a vacuum line which removes the loosened debris and water. An earlier series of tests had shown that the suction nozzle had to be within quarter of an inch of the surface for the suction to be most effective. The jets had, therefore, to clear a way for this nozzle by cutting down through the material and pushing it into the mouth of the tube, before the tube arrived.

For the first test a single nozzle (out of the three on the head) was used at relatively low pressure.

Figure 1. Clip showing a single jet cleaning through 2-inches of sand.

However if the jet pressure is raised to cut harder material, then the jet has enough power to wash the material under and past the suction tube so that only a small part of the solid is picked up and the path fills back up with the washed sand.

Figure 2. A higher-pressure cutting jet does not give the debris time to be sucked out of the tank.

If three jets are used, but with the jets directed so that the paths hit each other within the suction zone this stopping each jet going further for a long enough time that the suction can remove both water and debris. 

 Figure 3. A three-jet combination where the jets are held within the shroud, leaving a clean path.

For those unable to see the video the configuration of the jets meant that they met under the shroud as shown.

Figure 4 The jet configuration around the shroud.

When this is combined with a protective (flexible) outer shroud the final result was a tool that removes material without over-spraying into the surrounding sand and destabilizing it. Leaving a clean channel.

Figure 5. Larger head design removing a 2-inch thick layer of sand.

In a subsequent post I will include (when I can find it among the 200-odd hours of material) a video of a similar (though smaller) tool cutting a clean channel into a soft cement, and leaving a clean path behind it, as shown in the earlier post. For those interested the parts for these cleaning heads were assembled from plumbing supplies from our local hardware store at a cost, per head of around a hundred dollars or so. (back in 1995 when we ran the tests).

Waterjetting 35b - Cutting the Missouri Stonehenge video

The video that I posted last time did not fare as well as had been hoped, in making the trip from my computer to the blogger post, and so this week, to see if there are other ways of peeling the apple, I have also posted a copy of the video to Youtube, to see if this works better.

The video is of the making of the Missouri Stonehenge for which, as I have mentioned in a previous post, we used a jet pressure of around 15,000 psi with a flow rate of 10 gpm.

The video makes the point that a high-pressure jet system can, with relatively little support, cut a straight edge down the side of a block, even if there is only a very thin layer of rock to remove. It is normally very difficult to do this with a conventional cutting saw, or similar tool, which requires more material on the free side to stop the blade from being deflected away from the cut line.

If this new posting works as I hope, then I will be posting a number of different videos that have been collected over the years, but on Youtube initially, though I will provide the link as I have above.

Waterjetting 35a - an overview on video

This post is by way of an introduction to an occasional new feature of the site, where I will videos to different posts to help with understanding. Adding videos is not in my skill set, so this first is just a general overview of some of the ways in which waterjets have evolved over the years. I have tried adding one before, but this is the start of a little more of a concerted effort to use this medium. The overall video runs some 15 min 39 seconds.

 It is a compilation of different tapes made over the years, some of which are now otherwise unavailable. I’m going to let the overall video speak for itself with this first piece, but will then come back in subsequent posts to discuss some of the parts of the video. I hope you find it interesting.

As I mentioned I will break this into segments and discuss those in more detail later.

Waterjetting 34e - Hole completions and core removal

When I began writing about hole cutting and drilling, a month ago, I was intending to talk just about the relative efficiencies of cutting the core into larger pieces, rather than designing a cutting pattern that would completely cover the surface of the excavation, milling and removing the core in fine particles. Other topics intruded, however, and it is only now that I am going to conclude this theme by discussing that particular point.

Earlier posts have discussed how, by inclining two jet paths so that they come into close proximity within the target (or intersect in some cases) a much larger volume can be removed with no increase in input energy to the process. The gain in production comes from working out which are the best angles to set the cutting jets at, relative to the overall work piece.

Figure 1. Intersection of two jets in cutting clay. The cuts were made with the sample lying horizontally – in the actual operation the jets cut up and down vertically and the included wedge would normally fall out.

There is no universal rule for selecting the best angle for this, or for selecting the best relative depth for the intersection. It depends on the material being removed, and on the logistics and relative sizes of the hole being driven, and the components that fit into it. The material responses depend very much on the strength and structure of the material. The paths of both jets will have to intersect to remove materials such as steel, whereas with clays, and many rocks the two paths need only be relatively close at their lower end for the intervening rib to separate.

The problems are not just constrained to the removal of that core. One of the significant problems that exists even when using conventional techniques to drive tunnels and other large holes is that of making sure that the diameter that is being cut remains the same size as the tunnel advances. Because it is easier to break the rock within the tunnel wall, because of the release of the surrounding rock pressure, it requires additional effort to cut out beyond the projected perimeter in order to give enough space for the tunnel. With explosive blasting of the tunnel this means that the perimeter holes are drilled out beyond the projected tunnel line, and in cutting with a waterjet a similar strategy is required.

This problem is not normally that severe, since the size of the nozzles and support equipment are not that much larger than the jet that does the cutting, but, when the jet is cutting at the edge of the excavation the jet will need to be inclined outward by an angle of somewhere around 20 - 25 degrees in order to cut clearance.

An additional problem arises with the need to break the pieces being removed from the solid into small enough fragments so that these can be moved out of the way and into a transport line, so that the cutting head can continue to advance. In the case of the Soil Saw (for which Figure 1 showed one of the earlier test cuts) the nature of the clay was such that, once it was broken from the solid it disintegrated relatively easily and could be moved. Had this not been the case the cutting tool could not have passed without cutting the piece into smaller chunks. And in this regard, once a piece has been broken from the solid and is floating in a suspension within the cut, it becomes much more difficult to cut, since it can be deflected away from the jet before the full force of the jet can cut into it.

Further most materials are not as friable as clay – particularly those that are manufactured , and the pattern of cuts has thus to be designed so that the fragments are positively cut to the right size, to make sure they fit through the various gaps and feeds. For most of our work this meant that the pieces should be smaller than walnuts, and usually of around half-an-inch in size.

Ensuring that these cuts intersect in materials of varying properties will often require that the jets be designed to overcut in more favorable conditions, which wastes considerable energy. The alternative is to use the jets to cut relieving slots into the target, but to ensure that all the material is removed to the required depth on a pass by also including a mechanical component to the cut surface.

A cutting head designed by Rogaland Research shows the type of design required to achieve this, illustrating the angles of the two jets that will cut into the target as the head moves around the hole. In this case the design is to fit into a large diameter drill pipe to create a larger overall hole size.

Figure 2. The cutting head design developed by Rogaland Research (Vestavik, O.M., Abrasive Water-Jet Drilling Experiments, Progress Report, Rogaland Research, Stavanger, Norway, May, 1991.)

In this case the ribs of rock that are isolated by the jet cuts are removed by the action of the mechanical cutters in the second part of the bit.

Figure 3. Location of the jetted slots in the face of the drill-hole using the Rogaland tool. (After Vestavik)

In many cases the combination of a waterjet action to provide a free surface for the material to break to, and to relieve some of the confining stress on the material within the hole can significantly lower the mechanical forces required to break out the material. In such cases it makes much more sense to combine a waterjet action with that of a second removal device (which can be mechanical or thermal in some cases) to obtain a much more efficient combined system than that which would otherwise be the case. Where such systems have been used they have been shown to be more efficient in a number of cases than either of the component systems alone.

Unfortunately combining two systems to achieve optimal performance is not as easy as just merging the two sets of components, since there are additional benefits that come where the combination is further optimized so that the two parts work synergistically together. (One of the factors not included in the Rogaland design). I have written of this in the past, and will again soon.