The Process of Pipe Ramming
The process of pipe ramming is complex because it is not steerable, but often is very cost-effective.
Pipe ramming works on the principle of soil displacement and is an excellent method for pipeline installation where ground loss is expected due to shallow depth of installation. It is a casing installation method in which a pneumatic hammer slams the casing into the ground using repetitive percussive blows.
The pipe ramming method is non-steerable and hence there is little control over the line and grade of installation due to soil conditions and obstructions such as rocks and cobbles. However, it utilizes limited equipment and hence can be performed in places that are space-constrained and cannot support heavy equipment such as those required for directional drilling or auger boring.
Pipe Ramming Applications
Pipe ramming is most suitable for projects in the following situations
1. Projects in Soft Soil
Pipe ramming can be carried out in many different soil conditions except solid rock. It works best in soft to very soft clays, silts, and organic deposits, sands above the water table, and soils with cobbles, boulders, and obstacles lesser than the pipe diameter. Medium to dense sands below the water table, medium to hard clays, weathered shale, and soft or fractured rocks can also support pipe ramming but it may be difficult. In rocky ground conditions, pipe ramming can be carried out by first punching a pilot hole using a pneumatic tool, after which the pipe can be rammed in.
2. Projects with Shallow Installation Depths
Pipe ramming is an excellent method for the installation of pipes where ground loss is expected due to the shallow depth of installation because it utilizes the displacement principle, unlike other trenchless techniques. The advantage of installing different size casings without affecting surface structures such as roads and railway lines is a very attractive benefit.
3. Projects with Space and Muck Disposal Issues
Pipe ramming does not utilize a slurry system. The spoil generated is removed from the casing and only contains the soil’s natural moisture content, making it easier to handle. For other trenchless methods such as microtunneling, sufficient space is required for handling wet soil generated from the process. The spoil generated from pipe ramming is much lesser compared with pipe jacking or microtunneling.
4. Projects With Straight Runs
The pipe ramming process is not guided or steerable, and thus, pipes installed using this method are installed in a straight line. Pipe ramming can be used for horizontal, vertical, and angled applications. This type of drilling can be done at the required slope, but it can’t be done when a curved trajectory is required. For longer runs, sections of pipe one at a time can be installed or an entire length of pipe can be installed at once for projects with short installation lengths.
5. For Vertical Projects
Pipe ramming is typically used for horizontal installations under railroads and bridges but it can also be applied for vertical projects such as piling or micro-piling. An example of vertical application is an installation of vertical supporting piles from a bridge through a body of water when the bridge cannot support the weight of a crane necessary in a traditional method of installation of such piles.
6. Freeing Stuck Pipe
Pipe ramming can be combined with directional drilling to free a stuck pipe during pullback operation or a stuck drill pipe during pilot boring or reaming. The pipe can get stuck due to hydrolock or differential pressure sticking. To free the pipe that is stuck or slowed down, the ramming tool is attached to the end of the product pipe and the pipe is kept moving using the percussive action of the rammer.
Benefits of Pipe Ramming
- Pipe ramming is cost and time effective when ground conditions are suitable.
- Because of the smaller width and depth of pits, installation time can be reduced by 40%.
- Installation time is also reduced because 40 to 60 feet sections can be rammed in half an hour, compared to half a day when horizontal auger boring (HAB) is used.
- It can be used to install larger pipes over shorter distances, and also used for installations with shallow depth.
- It can be combined with directional drilling to free a stuck product pipe during pullback
- The accuracy of the pipe ramming method is usually better than ± 1% (both vertically and horizontally) of the length of the bore.
The Pipe Ramming Process
To begin, the pipe ramming equipment is aligned in the insertion pit in the direction that the pipe is to be installed. Insertion pits may not be required for embankments and slopes as the ram can be designed to start at the side of the slope. Thrust plates are not required for pipe ramming but guide rails are recommended to maintain the grade. The ramming pipes are made from steel conforming to ASTM specifications, with a minimum yield strength of 35000 psi.
There are two types of pipes used in the ramming process: closed-end and open-end pipes. The open-ended pipe is generally preferred as the ramming force required to drive the pipe is less. This reduces the chances of heaving and pipe deflection.
A closed-end pipe is used where using open-end pipe could disturb the stability of utility lines in the vicinity or cause surface subsidence due to lack of self-support from the flow of soil into the pipe.
The leading edge of the first pipe segment is fitted with a special welded band that protects the pipe and provides a slight overcut to reduce friction between the soil and the pipe. The nominal designed overcut is between ¼ inch and 1½ inch to reduce friction between soil and pipe. The ramming tool rams the pipe into the soil using repetitive percussive blows till the pipe exits at the receiving pit. Ramming can be done for an entire length of pipe or for shorter lengths depending on the availability of space and the prevailing ground conditions.
Compressed air powers the pneumatic hammer which rams the open-ended casing into the soil till it reaches the exit. To lengthen the drive, additional pipe lengths can be welded onto the casing. Periodic cleaning is required to lessen the drag due to the weight of the soil accumulated in the pipe. Spoil is removed by using compressed air or water jets for smaller diameter pipes and by augers for larger diameter pipes.
For shorter pipe segments, the first segment is rammed in and the ramming tool is returned to its original position. The next segment is then welded or fitted onto the first segment already in the ground and the process is repeated.
Pipe ramming lacks the precision of sonde-guided drilling or even microtunneling. It is faster than the pipe jacking method but matches the speed of auger boring or horizontal directional drilling operations. It is recommended to use steel casing pipe when using the trenchless method of pipe ramming.