What is thrust boring?
Thrust boring is a trenchless method for installing small-to-medium diameter utility pipes by jacking a steel casing through the ground from a launch pit to a reception pit, with a rotating auger removing the spoil as the casing advances. Thrust boring is used where an open-cut trench would be disruptive, costly, or impractical, and is one of the standard UK utility civils methods for crossings under roads, rail, watercourses, and obstacles.
Thrust boring is also known as auger boring. Both terms refer to the same method. BS EN 12889:2022, the current British Standard covering trenchless construction, uses auger boring as the formal term. Thrust boring is the industry shorthand contractors use day to day, and the two names are interchangeable across the UK utility civils sector.
Thrust boring is distinct from pipe jacking. Pipe jacking is a separate technique at a different scale, delivered by a specialist tunnelling trade: large-diameter structural tunnels installed with shields and segments. Thrust boring installs small-to-medium diameter utility pipes from a launch pit. The two are often conflated in casual usage, and the distinction matters because the kit, the crews, and the scheme size are all different.
How thrust boring works
Thrust boring works by pushing a steel casing through the ground in a straight line while a rotating auger inside the casing removes the spoil back to the launch pit. The whole operation runs between two small pits, with no continuous trench between them.
Setup and launch pit
A thrust bore starts with two pits. The launch pit holds the thrust boring machine and provides the working space for the jacking operation. The reception pit, at the far end of the bore, receives the casing as it breaks through. Both pits are shored to hold the ground back and are managed as confined-space excavations under HSE guidance. The launch pit carries a thrust wall (also called a reaction wall) that transfers the jacking force into the surrounding ground, which is what makes the forward push possible.
The bore
The thrust boring machine sits on a track inside the launch pit, aligned precisely to the design line and level. Hydraulic jacks push the first length of steel casing forward into the bore face. Inside the casing, a rotating auger fitted with a cutting head breaks the soil and conveys spoil back to the launch pit using the Archimedes screw principle. As each casing length is fully advanced, the jacks retract, a new length is added, and the push continues. The drive finishes when the casing breaks through into the reception pit.
Product pipe installation
Once the thrust bore is complete, the product pipe is installed through the steel casing. Some schemes use the steel casing as the permanent carrier and pull the product pipe through on centralising spacers. Other schemes withdraw the casing and leave the product pipe directly in the ground. Cementitious grout can be used to fill the annular space between the product pipe and the bore, which stabilises the pipe at the correct grade and transfers load into the surrounding ground.
Reinstatement of launch and reception pits
Launch and reception pits both sit in the highway, verge, or private ground. Pits in the highway fall under statutory reinstatement rules, set out in the Specification for the Reinstatement of Openings in Highways (SROH), 4th Edition. Reinstatement covers backfill, surfacing layers, materials, and guarantee periods. Pits outside the highway follow the landowner’s requirements and any scheme-specific specification. Either way, the finished surface is returned to its original condition before the crew leaves site.
When thrust boring is used
Thrust boring is chosen where a straight, short-to-medium crossing is needed and an open-cut trench is either impractical, disruptive, or not permitted. Most uses fall into three broad patterns.
Utility crossings under roads and rail
The most common use of thrust boring is a utility crossing under a road, rail line, or hard-standing. Thrust boring avoids closing the carriageway or the rail, keeps traffic flowing, and meets the line-and-level requirements that highway and rail authorities set for crossings. Gas mains, water mains, electricity ducts, and telecoms ducts are all installed this way on a daily basis. Where the crossing is under a motorway or an operational rail line, the scheme usually needs advance approval from National Highways or Network Rail under their respective crossing specifications.
Small-diameter drainage runs
Gravity drainage and gravity sewers need accurate line and level, because even a few millimetres of drift along a long run can compromise the flow. Thrust boring, particularly guided auger boring, is the method of choice for short gravity drainage runs where the pit locations, the crossing, and the design grade are all fixed. Thrust bore drainage is a standard use of the technique in UK utility civils.
Sensitive areas
Thrust boring suits schemes where open-cut would damage surface features or disturb protected ground. Typical examples include crossings under Sites of Special Scientific Interest (SSSIs), watercourses, ancient trees, archaeological zones, airport taxiways, and sports venues. The surface footprint is limited to the launch and reception pits, with no trench between them, which reduces environmental impact and reinstatement obligations.
Types of thrust boring
BS EN 12889:2022 recognises three main variants of auger boring that get grouped under thrust boring in industry use. Each variant suits different ground, distances, and accuracy needs.
Unguided auger boring
Unguided auger boring is the simplest form of thrust boring. The machine drives the casing in a straight line without any steering correction during the bore. Accuracy depends on the initial setup and the ground conditions. Unguided systems are cost-effective for short drives in firm, stable ground where minor drift is acceptable, for example a service duct under a driveway or a short carriageway crossing.
Guided auger boring
Guided auger boring adds a pilot bore ahead of the main drive. The pilot is a small-diameter tube pushed through the ground first, with its path monitored by a laser or optical guidance system. The operator makes steering corrections to keep the pilot on the design line and level. Once the pilot bore is complete, the main casing follows the same path, which gives accuracy of around +/- 1% of the drive length. Guided systems suit gravity drainage, longer crossings, and any scheme where design tolerances are tight.
Pipe ramming
Pipe ramming replaces the rotating auger with a pneumatic hammer. The hammer drives an open-ended steel casing into the ground in short percussive blows. Spoil is cleared from inside the casing at the end of the drive, either mechanically or with compressed air. Pipe ramming suits mixed ground with cobbles or obstructions that would stall a rotating auger, and is often paired with HDD on schemes where the ground is too variable for steered drilling alone.
Thrust boring compared with other trenchless methods
Thrust boring is one of four trenchless methods McFadden runs in-house, alongside horizontal directional drilling (HDD), moling, and pipe bursting. Each method suits a different combination of diameter, distance, and ground conditions. The four sit together in the no-dig and trenchless methods workstream.
The four trenchless methods McFadden performs, at a glance
| Method | Typical diameter | Typical distance | Best for |
|---|---|---|---|
| Thrust boring | 100mm to 1,200mm | 15 to 100 metres | Straight crossings under roads, rail, and obstacles where line and level matter |
| HDD | 25mm to 1,000mm+ | Up to several hundred metres | Long crossings, steerable paths, deep installs |
| Moling | 20mm to 180mm | Up to 20 metres | Service connections, short runs in soft ground |
| Pipe bursting | Host size or larger | Tens of metres per run | Replacing aged mains on existing alignments |
UK standards and industry bodies
Thrust boring in the UK sits inside a specific regulatory and industry framework. Three documents and two bodies cover the ground that matters on site.
BS EN 12889:2022 is the primary standard for thrust boring in the UK. Published by BSI on 30 November 2022, BS EN 12889 covers trenchless construction and testing of drains and sewers, including managed and steerable boring techniques. The standard distinguishes unguided, guided, and pipe ramming variants, sets out launch and reception pit requirements, and defines testing regimes for the completed pipeline. BS EN 12889 is the document UK contractors and clients reference when specifying thrust boring scope.
The Specification for the Reinstatement of Openings in Highways (SROH) is statutory guidance published under Section 71 of the New Roads and Street Works Act 1991. The 4th Edition came into force as statutory guidance on 10 May 2021 and was last updated in May 2025. SROH governs how the launch and reception pits for any thrust bore in the highway must be reinstated: backfill, surface layers, materials, and guarantee periods all follow the specification.
The United Kingdom Society for Trenchless Technology (UKSTT) is the UK industry body for trenchless methods, founded in 1993 and affiliated to the International Society for Trenchless Technology (ISTT). UKSTT publishes technical guidance, runs training and conferences, and promotes no-dig methods across the UK utility and civils sector. Contractors competent in thrust boring typically hold UKSTT membership or engage with UKSTT training.
Launch and reception pits for a thrust bore are excavations, and excavations have their own statutory framework. HSE guidance HSG150 covers health and safety in construction, including the shoring, edge protection, confined-space management, and daily inspection that every pit excavation needs. Legal duties sit under the Health and Safety at Work etc. Act 1974, the Construction (Design and Management) Regulations 2015, and the Confined Spaces Regulations 1997.
Thrust boring in practice
McFadden runs thrust boring as part of the no-dig workstream across Hertfordshire, London, Surrey, Essex, Cambridgeshire, and Berkshire. The technique sits alongside moling, pipe bursting, and directional drilling in the in-house capability, chosen where a straight utility crossing under a road, rail, or obstacle needs line-and-level accuracy and a smaller footprint than HDD.
Kit and crews
Thrust bore machines sit in the T. McFadden Plant fleet alongside moling rigs and pipe bursting kit. Crews are in-house, trained on the no-dig plant, and deployed as part of the same workstream that handles service installation, mains, and drainage. The kit matches the work: small-to-medium diameter utility pipes, short-to-medium drives, straight line-and-level.
Typical delivery
A McFadden thrust bore starts with a site survey and a services check. Launch and reception pits go in first, shored and managed per HSE excavation guidance. The drive runs from launch to reception with the auger and casing advancing together. Product pipe goes in through the completed bore. Pit reinstatement follows SROH 4th Edition. The whole job is run end to end by the McFadden crew without handing off to a third party.