Installing underground irrigation systems for parks and gardens has long been the domain of chain type trenching machines or backhoe excavators.   Whilst these methods are still used, it’s becoming increasing common for more modern techniques that minimise disruption and damage to the ground.  In particular, protecting the tree root systems of valuable trees throughout the park/garden.    Often referred to as Non Destructive Digging (NDD), these techniques achieve two primary objectives:

  1. Protecting valuable tree and plant roots.  This is incredibly important not only for the historic value of some trees, but also the cooling effect which tree canopies have on the environment.    City of Melbourne for example are aiming to double it’s tree canopy by 2040.
  2. Minimising surface disruption to parks or sports fields, which means they can be used almost immediately upon completion.

There are four main options for installing pipes/conduits underground.  We’ve listed them from least disruptive, to most:

  1. Directional Drilling (Boring) – The best of the Best!
  1. Hydro Excavation
  1. Vibratory Mole Ploughing
  1. Conventional Trenching

1. Directional Drilling (Boring)

Horizontal Directional Drilling falls under the umbrella of Non Destructive Digging (NDD) and involves a drill head being electronically guided under the surface in the desired location. The pipe is then pulled back through the bore hole created by the drill head and the pipe is installed with only a 60mm (approximately) bore hole effecting the soil.

The key benefit of directional drilling is when you are needing to install pipes within tree root zones. Conventional trenching and mole ploughing cut all the roots through the whole depth of the trench.

Directional drilling is also very helpful for installing pipes under hard surfaces and pathways that cannot be disturbed.

On the downside boring is a lot slower than conventional trenching or mole ploughing, but in some cases – as with established ornamental trees – is the only viable option.

2. Hydro Excavation

This is another form of NDD and this involves a high-pressure jet stream of water displacing the soil in the ground. This is followed by a larger bore vacuum hose sucking the mud slurry into a storage container usually mounted on a truck.

When working very close to large established trees Hydro Excavation is a great option, as it will not damage any roots at all.

The key benefit of hydro excavation is when working close to or immediately adjacent to utility services. By excavating with a water jet, you simply remove the soil from around a utility pipe without causing any damage to that pipe.

Hydro excavation is slow and expensive but mandatory in situations with services that need exposing.

In summary there are several options for modern irrigation system installation for parks, gardens and sports fields. Where the long-established methods are fast and relatively in-expensive, boring and mole ploughing methods are becoming more popular, as they don’t affect tree roots or playing surfaces in the same negative way as traditional trenching.

3. Vibratory Mole Ploughing

The mole plough uses the same actual machine as a conventional chain type trencher but with a completely different attachment called a mole plough.

A “knife” blade has a “bullet” shaped head at the end of it and the pipe is attached to the back of the bullet head, the knife moves up and down and cuts through the soil and turf as the pipe is pulled through underground.

The great advantage of mole ploughing is in protecting sports field surfaces. The narrow slit left after the knife has gone through can be wheel rolled over to close it up or rolled over with a small vibratory roller. The key benefit is that the field looks like no work has been done on it at all and the playing surface is ready for use straight away.  A bonus is that the pipe installation with a mole plough is very fast.

Mole ploughing can however struggle with tight and dry soil conditions which can rip up the surface significantly. Similarly, using a machine that is not heavy and powerful enough will also cause problems at the surface level.

4. Conventional Trenching

Most common in irrigation is the use of a ditch witch type chain trencher which has teeth that roll around a chain on a boom as the whole machine drives forward. This method is quick and the material that comes out of the trench is pliable and workable for easier backfilling.

In a similar way excavators or backhoes are often used and are handy for wider trenches.  However, the material produced is in big clumps- which is not ideal for backfill.

For sports fields, works close to trees or within close proximity to services, the two open cut methods above are not the best way to go.

The three following alternative methods of excavation have some real advantages.