Ramming Hammers for Supporting HDD Set Up

HDD has been around as a technique for several decades now and has become established as a significant and widely used technique in the area of new installations of pipeline, particularly for crossing works under roads, rail tracks and other significant obstacles/buildings where open trench operations would be difficult if not impossible.

However, on many occasions one of the most difficult aspects of an HDD project is setting up the drilling machine in less than favourable ground conditions, such as sand, gravel and similar ground conditions where the ground may have the propensity to ‘run’ if not correctly controlled. As these ground conditions are often found near the start point of a bore it can make launching the pilot drill head and drill string correctly into the ground at the required angle of attack difficult. This can caused significant problems in trying to establish the required bore path early in the pilot bore and may even cause misalignment of the bore that would require potentially time consuming and expensive remedial work to correct once started.

One method that has been developed to help overcome this set of circumstances is the use of the Hammerhead pipe ramming hammers to install a washover pipe through the less competent ground near surface to enable the drill string to reach a solid ground horizon effectively.

Washover Pipe Installation

To achieve the washover pipe installation, depending on the length and depth to which the pipe needs to reach, a length of steel pipe is set up at the launch point of the HDD bore on the line of the bore and at the inclination required for the start of the HDD pilot run. A HammerHead ramming hammer is then used to push the steel pipe into the ground. If the length of the washover pipe is greater than that of the first length of steel pipe, additional lengths can be welded onto the lead pipe as required.

The lead end of the steel pipe may be fitted with a cutting shoe to help maintain the advance of during the ramming process but also help maintain the desired direction of the ram. It may also assist in engaging the lead end of the washover pipe into the competent ground that it is intended to reach, minimising ground loss at the washover pipe competent horizon interface.
A pre-project site investigation will have determined the length and depth the rammed washover pipe will needed to reach to ensure the pilot drill head cuts into more competent ground and so establish the correct start for the pilot bore.
Once the washover pipe has been installed, spoil inside it can be removed if required. The pilot drill head and drill string is then launched from the drilling rig directly into the competent ground without having to negotiate the potential interference of the loose ground through which the washover pipe has been rammed.

It is usual that the washover pipe would be of a dimension that would allow the final installed pipe being pulled in by the drilling rig to pass through it to surface so as not to interfere with the final pipe installation.

Depending on the project requirements, in some instances the washover pipe may be extracted once the final product pipe has been installed using the HDD rig. This may allow a sub-surface connection to another section of the product pipeline to be made. But this is not always the case and the washover pipe may be retained in position as an added protection or casing for the product pipe as it approaches the surface.

Frank Gowdy, Sale Director for U Mole said of the technique:

“We have provided some of our HammerHead ramming hammers to clients for just this type of operation because the units are easy ti handle, powerful and cost-effective in what is often a limited access area on many HDD projects. The advantages that installing a washover pipe can bring to the start of an HDD pilot bore more often than out weigh any additional costs that this initial set up work may add to the project given the potentially huge costs of rescuing a bore that has failed in unstable ground before it really begun.”

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