From the magazine

Insights into pipe selection for trenchless projects

There are a number of pipe types currently available on the Australasian market, each with unique properties better suited to different installation and rehabilitation techniques. There is no one universal pipe material that is suited to all forms of Trenchless Technology.

Types of pipe

Polyethylene pipe

PE pipe is manufactured in Australia in sizes up to 2 m diameter (DN2,000). It is lightweight and flexible with an allowable bending radius of 20-25 times the outside diameter of the pipe. This flexibility reduces the need for fittings and makes PE pipe excellent in shifting soils, or for installation over uneven terrain.

PE pipe can be supplied in straight lengths or in coils, reducing the need for joints and fittings, and can be jointed using butt and electrofusion techniques or using mechanical fittings. Butt welding involves the heating of two pipe ends to fusion temperature and then subsequently joining the two ends by the application of force. In trenchless applications, butt welding is used to create one large pipe string with a smooth outside surface. This results in one homogeneous pipe with effectively no weak spots, which is a major benefit of PE that is not apparent for other pipe materials.

PE pipe has been used extensively in trenchless installation for many years. Some of the earliest uses of large-diameter PE pipe in trenchless applications are in directional drilling for river crossings. PE pipe is suited for these installations because of its scratch tolerance and fused joining system, which gives a zero-leak-rate joint with design tensile capacity equal to that of the pipe. To date, directional drillers have installed polyethylene pipe for gas, water, sewer mains, electrical conduits and a variety of other lines. These projects involved not only river crossings, but also highway crossings and right-of-ways through developed areas so as not to disturb streets, driveways, and business entrances.

Low density PE has high flexibility and retention of properties at low temperatures, however, is not generally suitable for trenchless applications. In HDPE, PE 80B has a minimum required strength (MRS) of 8.0 MPa as determined by regression analysis. In the past, this type of PE has been referred to as medium density PE or MDPE. The most suitable PE for trenchless applications is HDPE, specifically PE 100, which is the most recently developed polyethylene grade and has an MRS of 10.0MPa. PE100 has higher strength, higher slow crack growth resistance and higher toughness than earlier generation materials, which has led to its use in many trenchless applications.

The PE100 pipe specification covers pipe designed for pressure applications. There are three categories of PE100 pipe: standard, high melt strength and high stress crack resistant (PE100 HSCR). Standard PE100 is suitable for all pressure applications. In applications where very large diameter or thick-walled pipes are required, high melt strength PE100 offers a number of advantages around improved dimensional stability and increased throughput. In extremely aggressive installation conditions such as HDD through rock or a plough-in installation in rocky terrain, the extra protection of PE100 HSCR may be warranted.

PE pressure pipes are designated by their outside diameter or DN. For water and other general pressure applications, the maximum allowable operating pressure (MAOP) with a minimum service coefficient is designated by the pressure rating or PN. The standard dimension ratio (SDR) of a PE pipe is the ratio of the outside diameter and the minimum wall thickness. Pipes with a higher SDR have a thinner wall than pipes with a low SDR. The SDR can be related to the MAOP using the material MRS and the service coefficient appropriate for the application.

PVC pipe

PVC pipes offer many advantages for trenchless projects, including features such as long lengths, corrosion resistance, lightweight and ease of installation with minimum disruption.

With major successes in large scale pipeline projects for below ground applications such as sliplining and pipe bursting, PVC pipes are suitable for a diverse range of trenchless construction projects and are particularly effective in the rehabilitation of existing sewer and watermains.

The benefits of PVC pipe for open-cut construction also makes PVC pipe a superior choice for trenchless installations in capital improvement projects as well as rehabilitation. PVC pipe is manufactured in sizes compatible with cast and ductile iron pipes, thus facilitating its connection to existing pipelines.

With thinner walls than alternative materials for virtually the same pressure rating and hydraulic capacity, trenchless PVC projects enable a smaller hole to be drilled, allowing less spoil to be removed, thus reducing disposal cost.

GRP pipe

When pipelines are laid in densely populated areas, protected natural habitats, or beneath heavily frequented roads, jacking offers a minimally disruptive solution. Thanks to centrifugal casting, gravity as well as pressure pipes are manufactured with the compressive strength and wall thicknesses required to handle the jacking forces that are necessary to push the pipe and machinery.

GRP pipe features a smooth, nonabsorbent exterior surface, tight outer-diameter tolerances and comparably light wall structure and is suitable for very long and also curved drives.

Apart from providing excellent hydraulic properties, the mirror-like smooth inner surface is easily maintained and disinfected, adding jacking to the installation portfolio of potable water lines where hygiene plays a major role.

The pipes’ small outside-to-inside diameter ratio provides an array of advantages. For instance, smaller jacking machines are required for the pipes, which means lower equipment and lease costs, less excavation material, and a larger pipe capacity.

Being light-weight, corrosion resistant, easily jointed due to push-together joints and rigid to resist grouting forces, GRP pipes and NC Line Systems are ideal for relining applications. A maximal mass flow is above all ensured thanks to the smooth inner surface (small roughness coefficient) and the relatively light wall structure of GRP pipes.


The construction of pipes and underground conduits dates back thousands of years and is one of the earliest forms of civil engineering construction. The Romans developed cement and concrete similar to that used today. They mixed slaked lime with a pozzolanic volcanic ash from Mt. Vesuvius to produce hydraulic cement that hardened under water and would not deteriorate when exposed to moisture. Some pipelines and aqueducts constructed using this concrete are still in use today.

The oldest recorded modern-day concrete pipe installation is a sanitary sewer constructed in 1842 at Mohawk in New York State, US. It remained in operation for over 100 years. The French were the first to incorporate steel reinforcement in concrete pipe in 1896 (known as the Monier patent). The concept was brought to America in 1905 and to Australia in 1910. Since then, over 300,000 km of steel reinforced concrete pipe (SRCP) has been laid in Australia and New Zealand in drainage, road culvert, sewer and pressure pipe applications. Many of these pipes are still in operation and attest to the long service life of spun steel-reinforced concrete pipe. Indeed asset owners can now confidently plan on a 100-year service life for steel-reinforced concrete pipe.


Before selecting a pipe material, designers need to consider and establish the Trenchless Technology that will be utilised, taking into account variables including the pipeline design life, hydraulic capacity, working pressure, project budget, application, alignment, locality, soil or rock type, depth, pit access, groundwater (fresh and saline), existing pipeline condition and possible hydrocarbon soil contamination.

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