Everything you need to know about digging a trench

Digging a trench is an effective way to learn more about the soil and any hidden cables and pipes. Whether you’re planning a construction project or searching for cables, it’s important to do it properly. In this article, you’ll find everything you  need to know!

Digging trenches with suction excavation

What is a trench?

A trench is an excavated ditch used to examine the ground beneath. The purpose is to locate things such as cables or pipes, or to gain a better understanding of the soil structure. This is often necessary for projects like the installation of new infrastructure or for detecting underground cables. Properly carrying out a trench is crucial to prevent damage and ensure safety. By digging the trench carefully, you can check whether the theoretical location of the cables matches their actual position, and you can identify any unexpected obstacles or hazards in the ground more quickly. This helps avoid potential issues during the project.

Inspection cables and pipes in a trench

When should you dig trenches?

Digging a trench is often necessary for projects where you need to better understand the underground infrastructure. This is typically the case in the following situations:

  • Cable and pipe detection: When installing new cables or pipes to protect existing infrastructure.
  • Construction projects: For safe digging or foundation work, especially in areas with unknown soil conditions.
  • Street redevelopment: To check for underground utilities before excavation begins.
  • Water and drainage projects: To ensure there are no unforeseen obstacles in the ground.
  • Renovations of existing buildings: When undertaking underground work, such as laying new pipes or relocating cables.
  • Building a basement: To assess the soil structure and identify underground pipes before digging for the foundation.

Step-by-step guide for digging a trench

Step 1: Preparing

Before you begin any excavation work, it’s crucial to prepare thoroughly. According to legislation such as NRSWA, the party carrying out the excavation is often held liable for any damage to underground utilities. Therefore, it is essential to gather information about the location of cables, pipelines, and other infrastructure before starting the work. You can request this information from organisations such as the National Grid or relevant local authorities.

If your excavation is deeper than 30 cm, you must apply for a ‘Street Works Licence’ from the local council. This applies whether the work is on public or private land. When using mechanical equipment, you must also submit a Safety at Street Works notification. This ensures that the excavation work complies with safety standards and minimises the risk of damaging underground utilities.

It is also important to properly mark the excavation site, clearly define the depth and width of the trench, and choose the right method based on the work’s nature. These guidelines are further detailed in the ‘Code of Practice for the Installation of Utilities’, which ensures that excavation work is carried out safely and efficiently in accordance with regulations.

Marking the location with cones or tape

Step 2: Identifying and marking the location

Choosing the right location for the trench is crucial. It’s important to clearly define the excavation area. Mark the trench location clearly using methods such as:

  • Flags
  • Coloured dye or paint
  • Cones
  • Rope or tape

Step 3: Choosing a method for digging

Manual digging with a specialised spade

When digging a trench, a pointed spade is typically the best choice for loose or moderately compact soil. A pointed spade is ideal for firmer or harder ground. In
confined spaces or for more precise work, a smaller hand digger is useful. These spades provide control and precision, making them perfect for carefully digging
trenches without damaging pipes or cables.

Mini excavator

A mini excavator is a more compact machine, ideal for smaller to medium-sized digging projects. This type of digger is highly manoeuvrable and can easily work in tight spaces, such as gardens or narrow streets. A mini excavator is suitable for digging trenches in various types of soil and can create both shallow and deeper trenches. This makes it an excellent choice for projects like laying foundations, cables, or drainage systems. The mini excavator offers the speed and efficiency of a larger machine, but with the added benefits of flexibility and space-saving.

Suction excavator

A suction excavator excels at removing soil in delicate environments, ensuring minimal damage to underground infrastructure such as pipes and cables. This
machine uses high-powered suction technology, making it highly efficient and precise, even in tight or complex workspaces. If you’re looking for a suction
excavator for sale, keep in mind that this is often a better option for large companies or construction firms that require frequent use of the equipment. For individuals, hiring a suction excavator for specific projects is typically the most economical solution.

Carrying out trench excavation

Step 4: Carrying out the excavation

The excavation process begins once the trench is clearly marked and the area is secure. Start slowly and carefully, especially when you approach existing utilities
such as pipes and cables. If you are digging manually, use a specialised spade and work carefully to avoid any damage.
For mechanical excavation, such as using a mini excavator, you can work more quickly, but it’s still important to pay attention to the depth and edges of the trench. A suction excavator is ideal for digging in sensitive areas, as its powerful suction technique removes soil gently, reducing the risk of damage to underground infrastructure.

Step 5: Post-excavation Care and Inspection

After excavating the test pit, it’s essential to carefully inspect the area. Ensure the results align with your expectations and check for any damage to underground utilities or cables. Document your findings thoroughly for future reference. In the UK,this may involve reporting to:

  • Local Historic Environment Record (HER) or County Archaeologist (for archaeological findings)
  • Environment Agency or local authorities (if the excavation affects planning or the environment)
  • British Geological Survey (BGS) (if the excavation is geotechnical in nature)
  • Client or contractor (for construction-related activities)
  • Insurance company (only if damage has occurred)

Risks when digging a trench

When digging a trench, various hazards and risks can arise, which need to be carefully monitored:

  • Risk of trench collapse (Consider using trench shoring to prevent the trench walls from collapsing during the work and to ensure safety.)
  • Unsafe working conditions due to inadequate tools or insufficient protective measures
  • Electrical hazards from striking electricity cables

Frequently Asked Questions

What is a trench?

A trench is an excavated channel in the ground used to investigate soil structures and underground obstacles. The purpose is to gain a better understanding of the soil composition, the presence of cables or pipes, or to check for potential contamination.

Why is it important to dig a trench?

Digging a trench is essential for obtaining accurate information about the ground before construction or excavation work takes place. This helps to avoid unexpected issues such as contamination or hidden infrastructure and ensures better preparation for the project.

What happens to the soil removed from the trench?

The excavated soil is usually temporarily stockpiled or removed, depending on the project requirements and local regulations.

Are there any legal requirements before digging a trench in the UK?

In the UK, before digging a trench, you must check for planning permission, ensure compliance with Health and Safety regulations (e.g., CDM 2015), and verify
underground utilities. A street works permit may be needed for public roads. Always obtain landowner permission and ensure safe waste disposal.