Horizontal Directional Drilling (HDD) Information

Our capabilities

With our expertise, utilizing the horizontal directional drilling method, we have effectively installed pipelines with diameters up to 900mm. The materials installed are primarily polyethylene (MDPE/HDPE) and steel. We can achieve lengths of up to 500m in a single linear installation, known as a "drill shot" or bore. Drill routes can be installed on various grades and arcs, both horizontally and vertically. We're one of the few directional drilling contractors who routinely install gravity drainage pipework, even with tight falls. Using our drainage specific drilling methods and tooling, almost anything is now possible, and drainage installations are around half of our workload.

Full in-house design capabilities (Surveys, CAD, Calculations, Geotechnical Design among others)
Rock Directional Drilling for all utility types including gradient drainage
Single and multi-duct installations (single way, or multi way)
National Highways carriageway crossings, with CD 622 design, if required
Network Rail Under Track Crossings (UTX), including design to NR/L2/CIV/044
Main River Crossings, including design to FRA 3 criteria or environmental permit requirements
Canal Crossings, with design approvals from the Canal & River Trust
Active runway/ taxiway crossings
Installations on highly secure sites such as MOD, prisons and nuclear sites
Drilling under areas of protection i.e. SSSI, parks, heritage areas, woodlands
Installations under buildings, including drilling under active production lines
Gravity drainage and Rising Main installations, with falls as tight as 1:200
Installations using walkover tracking, up to 20m depth
Installations using gyro or wireline steering, for any depth and areas where walkover tracking is not practical
Low Voltage (LV), High Voltage (HV) and Extra High Voltage (EHV) installations, anything up to 400kV
Chemical pipelines to accommodate all nature of chemicals, no matter how corrosive
Ground source heating systems to greatly reduce massive heating costs
Town centre installations, the fastest method of installing pipelines in high vehicle and foot traffic areas
Installations through any type of material, even materials as hard as granite
Sub sea installations and outfalls

Considerations

Horizontal directional drilling installations can often be completed by ourselves, in a single length up to 500m, without the need for intermediate excavations. However, when feasible, these excavations can help reduce installation time, risk, and costs. We would always advise clients and principle contractors which approach we deemed most time, risk and cost effective, as well as providing various other route options and other trenchless solutions like Pipe Ramming, Auger Boring, or Impact Moling.

Directional Drilling is very good in most ground conditions, and SWDD have a >99% success rate of attempted installations. Typically, the method is well suited to clay, silt and sand based soils, even if containing gravel, cobble and boulders. Even rock of varying strengths is possible, and can even be a good drilling material, with the right equipment.

Generally HDD rigs are ~5-10m long for most installations, so it's often the case that if a drill rig can be accommodated on one side of the site, then the installation will be possible one way or another. The pipe normally is installed from the opposite side to the drill rig, but generally, as HDPE is often used, this pipe can be bent and laid out in suitable temporary work areas. Straight pipe lengths of HDPE which are butt-fusion welded, or coiled pipes can be used. Pipe coils are generally available up to 100m in length and 180mm in diameter, although longer lengths and diameters may be possible in some circumstances. Steel pipe can also be used, although this is much rarer than the use of HDPE.

HDD is generally not well suited to installations through difficult ground materials like pure gravel, cobble, boulders or where pipe diameters are large for their relative depth. Installations with a tight bend radius or tight falls can often be complex also.

There are often solutions or work arounds to overcome various problems, which SWDD have vast experience with.

Benefits

Horizontal directional drilling offers a number of advantages over traditional open-cut trenching methods, making it the preferred solution for many utility, pipeline, and drainage installations:

Minimal Surface Disruption – HDD allows pipelines and ducts to be installed without the need for continuous open trenches, reducing disruption to roads, footpaths, businesses, and residential areas.
Cost-Effective Solution – By reducing excavation, reinstatement, and traffic management costs, directional drilling can be a more efficient and economical option.
Environmentally Friendly – HDD helps protect sensitive environments such as rivers, woodlands, wetlands, and heritage areas by avoiding surface disturbance.
Greater Installation Depths – Capable of installing pipes up to 20m deep using walkover tracking and even deeper using wireline or gyro steering systems.
Versatile Applications – Suitable for installing water, gas, electricity, telecoms, drainage, rising mains, chemical pipelines, and ground-source heating systems.
Long Single-Length Installations – Capable of drilling up to 500m in a single bore, reducing the need for intermediate excavations.
Accuracy and Control – Using advanced steering systems, HDD achieves precise alignment and grade, making it ideal for gravity drainage systems with falls as tight as 1:200.
Suitable for Challenging Ground Conditions – With specialist tooling, we can drill through soft soils, mixed ground, and even extremely hard rock, including granite.
Safer for High-Risk Sites – Ideal for installations beneath highways, railways, airports, MOD facilities, nuclear sites, and environmentally protected areas, where open-cut excavation isn’t practical or permitted.
Future-Proof Solutions – Multi-duct installations allow for additional capacity, minimising disruption for future upgrades.

Basic Horizontal Directional Drilling (HDD) Method

Horizontal directional drilling (HDD) is a trenchless installation technique used to install pipelines, ducts, and cables underground without the need for open-cut trenches. This method is widely used for utility installations, river and road crossings, and environmentally sensitive areas where minimal disruption is required.

The process typically involves three main stages:

1. Pilot Bore

A small-diameter pilot bore, usually 100 mm to 150 mm, is drilled along a pre-determined path using highly steerable drilling heads.

We maintain precise control of the bore path both horizontally and vertically using walkover tracking, gyro steering, or wireline guidance systems.
Drilling generally begins from a launch pit and progresses towards a reception pit, but we can also steer the drill via intermediate excavations if required for accuracy or access.

2. Hole Enlargement (Reaming)

Once the pilot bore is complete, the hole is enlarged using a reamer to suit the required pipe size:

Back-reaming is the most common method, where the bore size is increased starting from the reception pit and working back towards the launch pit.
In situations where the reception area has limited access, we can also use forward reaming, working away from the launch pit instead.
Depending on the ground conditions and the final pipe diameter, several reaming passes may be required to achieve the correct bore size safely.

3. Product Installation (Pullback)

The final stage involves installing the pipeline, ducts, or cables into the enlarged borehole:

The product pipe is attached behind the reamer and pulled back through the drilled path.
Specialist swivels are used so that the reamer rotates while the pipe remains stationary, reducing torque on both the HDD rig and the pipe itself, ensuring a safe, damage-free installation.

In some cases, alternative techniques are used:

Pipe pushing – where the product pipe is pushed from the launch pit towards the reception pit.
Winch-assisted installations – where the pipe is pulled from the reception pit instead, depending on site conditions and access.

Drilling Fluid Management

Throughout the process, we circulate drilling fluid — usually a bentonite-based mud — to:

Remove cuttings from the borehole
Maintain bore stability
Reduce friction on the product pipe

Our HDD teams continuously monitor downhole pressures in real-time to ensure the installation is safe, efficient, and controlled, even in challenging ground conditions.