Who is a subcontractor? A guide for Civil Engineers and Construction Professionals

subcontractor

CPB contractor, cross river rail, subcontractor, WestConnex,

In Australia, a subcontractor is a business or individual hired by a main contractor to handle specific tasks or services within a larger project.

In Australia’s construction industry, subcontractors are the backbone of almost every major project. It’s often subcontractors—rather than the head contractor—who carry out most of the physical work on site. But who exactly are they, what role do they play in civil engineering and construction projects, and what challenges do they face in this high-risk, high-pressure environment?

At its simplest, a subcontractor is a business or individual engaged by the main contractor (sometimes called the principal contractor or head contractor) to perform specific tasks or provide specialised services that form part of a larger project.

The head contractor manages the overall project and deals directly with the client or government agency funding the work. Subcontractors, on the other hand, focus on delivering their specific piece of the puzzle. This could range from earthmoving and formwork to electrical installations, steel fabrication, bridge building, or even specialist engineering services like tunnelling or rail track laying.

Subcontracting in Australia

In the 2022-23 financial year, the construction industry generated AUD $568 billion in total income and employed about 1.3 million people. Notably, the Construction Services subdivision – which includes trade contractors and subcontractors – contributed roughly $248 billion of that income.

This means nearly half of all construction activity by value is delivered via subcontracting arrangements. In fact, earlier ABS data showed that about 40% of all construction industry revenue came from subcontracting (and an even higher 79% of revenue in the construction services segment) (Source: ABS).

Roles and Responsibilities of Subcontractors

In engineering and civil infrastructure projects, subcontractors perform specialized tasks under the coordination of a head contractor. Common roles and services subcontractors provide include:

  • Site Preparation and Earthworks: Clearing, excavation, drilling and site grading performed by earthmoving contractors.
  • Structural Works: Steel fixers, concreters and formwork carpenters who build the structural framework, pour concrete, and reinforce structures.
  • Building Installation Services: Trades such as electricians, plumbers, HVAC technicians, and scaffolders who install essential building systems.
  • Infrastructure Specialists: For civil projects, this includes bridge and tunnel construction crews, rail track installers, road paving teams, and utility installation contractors.
  • Finishing and Completion: Painters, tilers, landscapers, and other finishing trades who complete the project details.

Major Subcontracting Companies and Project Examples

Major engineering projects in Australia are delivered by consortia of big contractors, who in turn rely on numerous subcontractors. Below we highlight a few recent landmark projects – WestConnex, Inland Rail, Cross River Rail, and Snowy 2.0 – and the subcontracting companies involved:

WestConnex (Sydney)

WestConnex is Australia’s largest urban road project, involving 33 km of new motorways and tunnels in Sydney. It was delivered in stages by joint venture contractors. For example, the WestConnex New M5 tunnels (now part of the M8 Motorway) were built by a JV of CPB Contractors (CIMIC Group) with overseas partners Dragados (Spain) and Samsung C&T (Korea) (Source: CPB).

The final M4-M5 Link Rozelle Interchange was delivered by CPB Contractors in a 50:50 joint venture with John Holland. These tier-1 firms acted as head contractors, but they subcontracted significant packages: tunneling specialists, electrical and mechanical fit-out crews, traffic management, and countless trade subcontractors for concrete works, formwork, steel fabrication, etc. Design and engineering consultancies like Arcadis, AECOM, and WSP also served as subcontracted consultants on WestConnex, providing civil and structural design services.

Cross River Rail (Brisbane)

This is a $5.4 billion project to build a 10.2 km metro rail line (including twin tunnels under Brisbane River and four new underground stations). Delivery is split into major work packages involving alliances of contractors and subcontractors.

The Tunnel, Stations and Development (TSD) package is a public-private partnership led by the PULSE Consortium, which includes CIMIC Group companies (Pacific Partnerships, CPB Contractors, and UGL) along with international partners like Ghella (Italy) and DIF (an infrastructure fund).

The Rail, Integration and Systems (RIS) package is delivered by the UNITY Alliance – comprising CPB Contractors, UGL, AECOM and Jacobs, and partners HASSELL, RCS Australia, Acmena, Martinus Rail and Wired Overhead Solutions.

A third alliance with Hitachi Rail is implementing the new signaling system. Crucially, Cross River Rail has placed heavy emphasis on local subcontractors: by late 2023, more than 1,500 Queensland-based subcontractors and suppliers had contributed to the project (Source: Queensland Government) with about 90% of project expenditure going to Queensland companies.

One example is Formcon, a local civil subcontractor that performed concrete and reinforcement works for the new Exhibition Station in Brisbane – pouring over 3,700 cubic meters of concrete and installing 1,000+ tonnes of rebarThis illustrates how major public projects can benefit smaller subcontractors, providing them significant work and enabling them to hire apprentices and expand their businesses

Subcontracting challenges

However, subcontracting isn’t without its challenges. Large projects can involve hundreds of subcontractors, leading to complex layers of management and coordination.

Miscommunication between subcontractors and the head contractor can result in delays, rework, or safety risks. On projects like Melbourne’s West Gate Tunnel, for instance, subcontractor disputes and cost blowouts have made headlines, illustrating how difficult it can be to keep such massive operations running smoothly.

Subcontractors also take on significant risks. Unlike permanent employees, subcontractors are often paid per project or milestone.

If a head contractor experiences delays, funding issues, or insolvency, subcontractors may face late payments or, in worst cases, may not be paid at all. This is a serious concern on large infrastructure projects where cash flow is king.

The collapse of companies like Probuild highlighted just how vulnerable subcontractors can be when major contractors fail financially, leaving smaller businesses unpaid despite having completed their work.

Then there are safety and compliance responsibilities. Subcontractors must adhere to stringent Australian workplace health and safety regulations, environmental protections, and quality standards.

On high-risk civil engineering sites—such as bridge construction or underground tunnelling—this means significant investment in training, equipment, and insurance. A single safety breach can result not only in fines but also in long-term reputational damage that makes winning future contracts difficult.

Subcontractors also face the challenge of balancing multiple projects at once. A concrete supplier might be working simultaneously on a highway upgrade in Queensland and a wind farm project in South Australia. Managing crews, machinery, and logistics across such distances requires exceptional planning and leaves little room for error.

Despite these challenges, subcontractors are essential to building Australia’s infrastructure. They bring flexibility, innovation, and technical expertise that head contractors often cannot maintain in-house.

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