New installation of pipe and duct which may be used as a main pipeline or carrier pipe for other services for gravity or pressure networks.
Pipe Ramming is applicable for gas, water, cable, sewer and fibre installations particularly where the rammed installation is being used as a carrier pipe for other services. Ramming is achievable in diameters up to around 4.5 m depending very much on soil type and the selection of the ramming tool which has to be matched the prevailing conditions and requirements. Installation lengths may be up to 100 m again depending very much on prevailing ground conditions
Limitations are that the installation is not steerable and care should be taken in the set-up of the ramming hammer to ensure the best outcome of the process. Thorough ground investigation should also be undertaken to ensure that ramming is the correct process to use given potential obstacles that may be encountered.
Vertical applications such as piling and HDD assist and rescue are also possible.
Ramming can offer:
- less disruption and damage to surfaces worth conserving and minimal restoration as it eliminates trenching and open face ramming eliminates potential ground heave even at shallow installation depths
- low social costs as the trenchless installation technique does not impact greatly on traffic management or the local population
- no jacking abutments or auger cutters required
- the soil core remains in the pipe during ramming (unless closed face ramming is used), which means that there is limited ingress of water when rivers or high water table areas are encountered
- minimal depth of cover required so shallower excavations possible unless closed face ramming is used where there may be some degree of ground heave as spoil is compressed around the outside of the rammed pipe
- adaptable for all pipe diameters with special ram collets which sit between the pipe being rammed and the ramming hammer
- a technique that is widely acknowledged and accepted as a realtively simple technique
- short set-up and installation times
- a wide application range.
Whilst basically the same principle as impact moling, in pipe ramming the ramming hammer is used in a different way altogether. As opposed to using the impact energy to displace soil directly around the outer shell of the hammer unit, a ramming hammer’s energy is used to push a steel pipe section into the ground from a start pit. The pipe installed can be used either as a pipe in itself or as a carrier conduit for separately installed services.
On a typical installation the first section of steel pipe is placed in the start pit on the correct line and level for the installation. The ramming hammer is attached, via a series of size adaption collets, to the rear of this pipe. The hammer is operated and the reciprocating piston drives the pipe section forward directly into the ground. Ground conditions on such a project are vital to the success of such work and should be very well understood before attempting such an installation.
Normally, installations are achieved using an open-ended pipe so that the cutting edge is only that of the pipe (which is often fitted with a cutting edge or shoe before commencing the ram). The ground into which the pipe is rammed then forms a plug inside the pipe. When ramming over the required distance is complete or at discrete distances along the ram this spoil is removed using compressed air pressure, water jets or scrapers, ultimately leaving the steel pipe in place as required. As with impact moling the ground conditions and unexpected obstacles can cause the pipe to deflect from the required course. So, the system is often used only where precise line and level tolerances are not required. Therefore for gravity sewer applications it can only be used as a casing pipe within which a sewer is laid to the required gradient.
Ramming can also be achieved using closed end pipes where ground conditions may not be conducive to open ended techniques. Here the soil is compressed around the advancing pipe in similar fashion to that achieved during impact moling. This is a less utilised technique due to the potential for interference with nearby services and possible ground heave as the soils around the closed end hammer are compressed/pushed aside.
Using ramming techniques it is also possible to achieve pipeline replacement given that the rammed steel pipe may be installed at a diameter greater than that of the original pipe (which is in deteriorated state) by ramming it concentrically around the old pipe but along the same route. The soil and old pipe can then be removed from within the newly rammed pipe leaving the replacement pipe in-situ once cleaned out.
Ramming hammers also has application in the Horizontal Directional Drilling (HDD) sector. The use of the ramming hammer in this instance is designed to add impetus to the drill string over and above that capable by using the drilling rack driving force alone. This may be to add force at the drill head to overcome particularly difficult ground conditions or during pullback to add pulling force as the product pipe is being drawn in.
In cases where during HDD operations the drilling string becomes stuck, the use of a ramming hammer attached to the string may be sufficient to aid release of the drill string thereby negating to dig out or abandon the drilled bore.
Further to this ramming may also be used as a preliminary operation prior to or as an assist to HDD operations where near surface ground conditions require that a lead pipe is installed from surface down to the drilling horizon to prevent loss of the pilot bore due to bad ground conditions such as gravel beds. Here the ramming hammer is used to install a steel pipe angled at the attack inclination required by the drilling rig. The pipeline installed would normally be of a diameter large enough that it will accommodate the final product pipe diameter being drawn into the bore by the HDD machine.