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Slurry Boring

From EverybodyWiki Bios & Wiki

Slurry boring machines are tools used to bore a hole underground between two points without disturbing the surface ground. This open air chamber is referred to as the bore hole and is used to either run ducting for product or the raw product itself between the two points.

Uses[edit]

Slurry boring, also known as slick boring or wet boring is a straight line underground boring method used for installing utilities such as water, sewer, gas and communications lines. Small slurry boring machines are used for boring under roads, driveways, structures, landscaping and in any other situation where it is desirable to keep surface destruction to a minimum. They use rotating method to turn the drill rods or drill string. It is a less expensive alternative to Directional Boring or HDD rigs.

How it works[edit]

A slurry boring machine typically sits on some type of skid or rail of a particular length that allows a certain amount of travel or stroke. There are small boring machines that do not sit on a skid or rail rather they are wheeled or even handheld.

Pit machines sit in a boring pit that is dug with a backhoe, hydraulic excavator or by other means. Drill rods that are accommodating to the length of the stroke of the machine are attached and advanced until a come out pit is reached. The first drill rod will have a pilot bit for cutting or otherwise displacing the soil or material it is boring through. Water is injected through the rods and out of the end of the pilot bit via a mechanism called a water swivel. The primary purpose of the water is to flush the cuttings or spoils out of the hole. In slurry boring water is not used for jetting or in any way to cut the material being bored through. A secondary purpose for the water can be to introduce agents into the bore hole either for stabilizing it, breaking down reactive clay so that it can be more easily flushed out of the hole or for assisting in heat transfer to cool the bit and reduce wear. If a larger hole is needed the pilot bit can be removed, a reamer installed and the hole enlarged by turning and retrieving the reamer in a process opposite of the pilot hole being bored.

Performing a bore[edit]

A sight survey is done to determine where the bore pit and come out pit need to be in order to most efficiently cross under the surface obstacle. A bore pit is dug to a size that accommodates the machine and whatever crew is needed to operate the machine and perform any other tasks needed to complete the bore. A come out pit is dug on the other side of the obstacle large enough to receive the pilot bit, taking into account and inaccuracies in aiming, and to work in if needed. Depending on the depth of the pit shoring may required. Once both pits are prepared the boring machine is lowered into the hole and set up. Measurements are taken to determine how many drill rods will be needed. An initial drill rod with a pilot bit will be attached. The rod will be aimed at the come out pit by slight adjustments to the direction the machine is facing. If a grade needs to be maintained, for sewer line fall for instance, the angle, up or down, in which the machine bores can be adjusted accordingly. Likewise, On longer bores some elevation may be needed on the machine to account for any drop in the drill string. The bore begins by advancing the first rod until the machine cannot advance that rod any farther. The rod is disconnected from the machine and backed up on the rail or skid far enough to make room for another drill rod. That drill rod is connected to the rod already in the pilot hole and to the machine. The new rod is advanced in the same manner. Rods are added until the come out pit is reached. Counting the rods as they are added, knowing the length of rods allows the operator to know how far he has bored and how much farther he has to go.

Once the come out pit has been reached the pilot hole is complete. if it is large enough to accommodate the utility being installed the rod can be removed from the hole. If the hole needs to be larger a reamer can be installed in place of the exposed pilot bit in the come out hole and used to ream the hole larger. This is done by turning the reamer in the same direction as was used to bore the pilot hole and retracting the rods. The machine will move backwards along the skid or rail until a full drill rod is exposed and can be uncoupled from the machine and drill string and removed. The machine is then advanced forward to the drill sting still in the bore hole, coupled to it and the reaming process continues until the reamer is retrieved back at the bore pit. At this point the machine may be removed from the hole to install the utility. A cable may be pulled back during the reaming process that can be used to pull the pipe or other utility through the hole. This is usually done after the hole is completed but smaller pipes, cables and conduits can be pulled through as the reaming is taking place.

Limitations and Advantages[edit]

Slurry boring machines do have limitations. They cannot bore for long distances in the way that directional boring rigs can. The bit cannot be steered in the way a directional rig can steer. When encountering rock the process can slow down considerably. Water is needed so a water supply needs to be accessible either from a tap or transported to the site with a tank and pumped under minimal pressure to the machine. No sleeve is installed during the boring process like a jack and bore so the bore hole can possibly cave in under the right circumstances such as too much granular soil. Bentonite clay can help stabilize bore holes.

Slurry boring machines are typically less expensive than Hydraulic Directional Drilling rigs. For utility installation such as water and sewer lines that just need to cross a road the crew size and ancillary equipment needed will be much less also contributing to a lower cost of performing the bore.

Because they use water to evacuate the cuttings from from the bore hole instead of an auger they require much less horsepower to run than an auger boring machine.

Slurry machines are more accurate than pneumatic boring tools known as missiles or hole hogs. Because slurry machines have a rotating bit they can cut through obstructions that would stop or redirect a pneumatic tool.

References[edit]

https://www.trenchlesspedia.com/definition/2955/slurry-boring


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