2 June 2025
Impact moling is the most commonly used trenchless method for laying or repairing small diameter pipes, cables and ducts, without the need for extensive excavation.
While pretty much everyone in the utility industry knows about impact moling, there are still misconceptions around this technique – and this article aims to put them right. Here’s everything you need to know about impact moling, from the UK’s leading supplier and manufacturer of pipeline distribution equipment and tooling.
What is impact moling?
Impact moling is a trenchless technique for installing or replacing pipelines. It involves using a pneumatically driven machine (known as a “mole” or “soil displacement hammers”) to create a bore through the ground. The mole displaces soil as it advances, forming a tunnel for the pipes or cables to be installed in.
Because there’s no need to excavate, it’s a great option for laying services under roads, driveways and landscaped areas without disturbing the surface.
What are the key advantages of impact moling?
Impact moling stands out as one of the most efficient and non-invasive methods for installing underground utilities. Its biggest strength lies in its ability to get the job done with minimal surface disruption. Instead of digging a continuous trench, only two small pits (an entry and exit point) are required. This makes it ideal for projects under roads, driveways, or landscaped areas where preserving the surface is critical.
Another major advantage is speed. Impact moling is fast to set up and operate, significantly reducing project timelines compared to traditional excavation. Less time on site means less disruption to traffic, homes and businesses.
Safety is a significant consideration, and where impact moling is a great choice. Without the need to excavate, the operator can drastically reduce the risk of cable strikes or other potential injuries that can occur with open trench digging.
Cost savings also come into play. Since there’s little to no surface reinstatement needed, and reduced labour and machinery use, the overall project cost drops. Add to that the lower environmental footprint- less fuel use, less waste, and reduced carbon emissions- and you get a method that’s not only budget-friendly but also environmentally responsible.
Impact moling is also incredibly versatile. It works well in various soil types, especially softer grounds like clay or silt, and is suitable for installing a range of services including water pipes, electrical cables and telecoms ducts.
For utility providers and contractors impact moling offers a smart, clean, and efficient way to get underground work done with minimal hassle.
Impact moling limitations
While impact moling is an efficient and low-disruption trenchless method, it’s not without risk, especially if poorly planned or executed.
Unsuitable ground conditions
Cobbles, dense dry clays and solid rock are not compatible with this type of trenchless installation. These ground conditions can slow down the process, cause surface disturbance or cause the mole head to stray from the bore path.
Distance from nearby utilities
The pneumatic hammering action of the mole can create vibrations that may affect nearby structures or utilities. In particular, older or fragile pipe materials like asbestos cement are more susceptible to minor damage during installation. However, planning and correct site maps can be used to mitigate this.
Operator skill
Operator competence is essential for impact moling. A knowledgeable team will conduct detailed surveys and have a solid understanding of the different types of moling equipment, accessories, and best practices on how to use them.
A brief history of impact moling
The concept of impact moling was developed by the German company Essig in 1966, but it didn’t reach widespread adoption in the UK until the 1980s.
The 1980s and 1990s saw significant advancements in trenchless technology, with the development of methods like pipe bursting and horizontal directional drilling (HDD). These techniques expanded the capabilities of trenchless installations, allowing for longer distances and larger diameters. With the establishment of the United Kingdom Society for Trenchless Technology (UKSTT) in 1993, this further promoted the adoption and development of these methods.
Today, trenchless techniques, including impact moling, are widely used for installing and rehabilitating underground utilities.
How impact moling works
Impact moling works by driving a torpedo-shaped metal tube through the ground with a hammer to form a tunnel (known as a “borehole”) under the ground. A pipe or cable is then fed through the tunnel in the space left behind. Most impact moling machines used pneumatic power, with a different mole head used for different ground conditions.
The air-powered pistons used to drive these earth piercing moles through the soil are suitable for a range of compressible ground types, including clays, silt and peat.
This method can be used to cover short distances in 15m sections – and is typically used for pipes with a diameter between 25mm-63mm (although, in the right conditions, can be effective for pipes up to 160mm in diameter).
Here’s the installation process, step-by-step:
- Excavation – two pits are excavated (an entry pit and a reception pit)
- Alignment – the mole is carefully aligned in the entry pit and driven forward in a straight line
- Insertion – the pipe can be towed through the boring process, or inserted after the borehole has been made – depending on soil stability
How is this technique used?
The key sectors that utilise impact moling include utilities, construction, telecommunications, infrastructure and landscape gardeners.
Impact moling is suitable for installing:
- Water pipes
- Gas pipes
- Electric cables
- Telecommunication ducts
- Irrigation systems
- Drainage and sewer pipes
It’s commonly used in both residential and commercial settings – essentially, anywhere that it’s important to preserve the existing surface.
Moling vs other trenchless techniques – which should you use for your project?
Impacting moling is just one of the methods covered by trenchless technology. And while it’s ideal for certain applications, it’s not always the right choice. Here’s how it stacks up against other common methods…
Impact moling
- Best for: Short-distance installs (up to 25–50m, in 15m sections), small-diameter pipes or cables (usually ≤160mm), soft ground conditions.
- Pros: Quick setup, minimal surface damage, cost-effective, no need for large equipment.
- Cons: Non-steerable, not ideal for rocky soils or precise path control.
Horizontal directional drilling (HDD)
- Best for: Longer distances, larger diameters, and when precise navigation is required (e.g., under rivers or busy roads).
- Pros: Highly steerable, can navigate curves, works in a wide range of soils.
- Cons: More expensive, requires complex equipment and skilled operators.
Pipe bursting
- Best for: Replacing old, damaged pipes with new ones of equal or larger diameter.
- Pros: Replaces pipe while creating a new path, minimal surface disruption.
- Cons: Requires access to the existing pipeline and specialised tools.
Not sure which technique and tools are best suited for your next project? Get in touch with our expert team and we’ll be happy to advise.
Selecting the right impact moling equipment
The right equipment is key to a successful trenchless installation. Hy-Ram Engineering offers a range of impact moles and accessories designed to meet various project requirements. Here’s a guide to help you choose the appropriate equipment:
1. Determine pipe diameter and bore length
Hy-Ram’s impact moles come in sizes ranging from 45mm to 180mm, suitable for installing pipes or ducts from 20mm up to 160mm in diameter.
2. Assess soil conditions
Impact moling is most effective in compressible soils like clay or silt. It’s less suitable for rocky or sandy soils, where alternative methods like pipe ramming may be more appropriate.
3. Fixed vs moving head moles
Hy-Ram offers both fixed head and moving head moles. Fixed head moles are ideal for straightforward, linear installations, while moving head moles provide better navigation through varying soil conditions. Your choice will come down to how complex the installation path is and soil variability.
4. Choose the right accessories
Keep your equipment effective and safe to use with the right accessories. At Hy-Ram, we can supply the relevant PPE and lubrication for your soil displacement hammers and impact moles.
5. Consider equipment hire
If your project is short-term or requires specialised equipment, hiring may be more cost-effective than purchasing. Hy-Ram offers equipment hire services, providing flexibility and reducing capital expenditure.
Find the right tools and equipment for your pipeline installation work
At Hy-Ram, we bring decades of expertise when it comes to delivering quality pipeline installation, repair and maintenance equipment. We provide access to a wide range of high-performance impact moling tools, whether you’re looking to buy them outright or hire specialised equipment for a one-off construction project.
Contact our team of trenchless technology experts to learn more about our impact moling tools and which equipment is best suited for your project.
