Ground conditions, river bed profile and high tidal ground water levels would require very high cost excavations for any tunnelling or auger boring technique. These methods would also be significantly slower than the chosen method of Horizontal Directional Drilling (HDD).

HDD is a surface launched steerable technique and for the river crossings at Sandwich would need to pilot a curved profile dropping to around 5m below river bed or 11m below the ground level of the entry and exit points.

The main difficulty for the HDD project was the lack of working space either side of the river. The available working area south side of the river was congested with existing services, development, allotments and public rights of way. To the north side the available space was limited by SSSI and boundaries. The crossing length available was 125m and due to the lack of suitable areas for the steering survey equipment and salt water table around the river usual tracking techniques were not possible.

Allen Watson Ltd determined that the only way to negotiate the steering of the crossing was to utilise a North Seeking Gyroscopic steering tool. Gyros are unaffected by magnetic interference (from pipes, cables, saltwater, shipping) and require no additional access along the route of the drill to maintain accuracy so the footpaths and allotments could remain open at all times.

Firstly 3no. separate pilot holes were drilled in 3.5 days. The 450mm hole was then reamed (upsized) to 600mm before the pre-welded string of pipe was pulled in. The 500mm and 180mm pipes followed, with all drilling works taking 3 weeks. Throughout the project used drilling fluids were returned from the north side to the drilling rig by pumping through drill pipe in one of the other bores. At the drilling rig the fluids were cleaned through a multi-stage process and recycled throughout the project only being disposed of at the end.

All personnel had to meet the requirements of the eight 2O Orientation and Thames Water Passport this included all persons being CPCS certified for the activities they were to undertake, and all operators were required to undertake a full medical.

Cappagh Construction undertook the construction of the drive and exit shafts and following pipe installation coupled the pipelines through the drive shafts and back fill the excavations. AWL undertook all the guided auger boring activities.

Cappagh Construction constructed the caisson shaft at depth ranging between 4- 6 metres with the reception shafts constructed by using a 3-metre trench box with road plates at the front and back of the box.

AWL used its own GAB 85v guided auger bore machine with optical electronic navigation for all the installation of 3 drives which ranged in length between 30 and 80 metres. Ground conditions changed from clay with chalk deposits to chalk with a high level of flint, which required the full 18,000Nm of rotary torque developed by the GAB 85v machine to rotate the flight augers in the hard ground encounted.

A third pipeline needed to pass beneath a CLH-PS fuel pipeline. To ensure that the ground movement beneath the CLH-PS pipeline was inside the acceptable limits the pipeline had to be exposed and monitored by authorised personal while the installation of the jacking pipes took place.

Following installation, the pipelines were connected and fully tested in accordance with EN610.

Compact equipment that can operate from shafts or pits as small as 2.40mØ, Guided Auger Boring is powerful and versatile with jacking forces of 85te up to 260te that can install a variety of pipe materials, including vitrified clay, steel, PE, concrete or GRP.

A cost-effective alternative to open cut, Guided Auger Boring is unaffected by surface obstacles. Ideal for installations where precision is paramount, with accuracy of +/- 25mm over distances of up to 120m between pits.

• Steel pipes and ducts from 100mmØ – 914mmØ or drainage pipes from DN150 up to DN900

• Under railways, roads, rivers, airports, buildings, contaminated land and SSSI

• Crossings can be for Water, Oil, Gas, Electricity, Sewerage, Chemicals, Communication Ducts and Outfalls

Horizontal Directional Drilling (HDD) or Horizontal boring as it sometimes known, provides a safe and cost effective solution for the installation of pipes, ducts and cables where conventional open cut methods are not permitted, practical or viable. Horizontal Directional Drilling (HDD) causes no disruption to roads or rail, does not scar the landscape and works from the surface, meaning this trenchless method is suitable for environmentally sensitive areas.

This prevents the need for costly and inefficient trenching methods which are harmful to the environment and create massive amounts of waste materials. As with most trenching operations the impact on local surroundings can be massive and extremely unpleasing whilst also bringing very high installation costs. It will reduce those costs enabling total project costs to be more feasible.

With this method, we can install pipelines of almost any material, with diameters ranging from 25mmØ – 1,200mmØ in distances from 15m – 1,500m installed in one single operation.

We own and operate the most technologically-advanced directional drilling equipment, with pullback forces ranging from 14te up to 300te, and with over 40 years of experience are able to complete small, medium and major pipeline projects throughout the UK and Ireland.

• No environmental disruption as surfaces are not broken up or damaged to any great extent
• Minimal traffic disruption
• Approved methods for pipe laying from 25mm to over 1200mm diameter over 1.5km.
• Fast turnaround.
• Full UK and Ireland coverage.
• Very economic for river crossings, railway crossings, highway crossing and roundabouts.

• Water
• Gas
• Electric Supply
• Telecommunications
• Rising Mains
• Gravity Mains

Pipe Bursting is a trenchless method for replacing buried utility pipelines such as sewer, water or gas pipes without the need for a traditional open trench construction.

Pipe bursting sometimes referred to as Pipe Cracking, Pipe Splitting, Pipe Eating, Pipe Displacement and Pipe Replacement can be either pneumatic, hydraulic or static pull.

Pipe bursting can also be used to increase pipeline carrying capacity by replacing smaller pipes with larger known as “upsizing”. Allen Watson Limited have experience in both size for size replacement and upsizing pipelines.

Pipe bursting is a trenchless means of replacing a current pipe utilising an existing but failing asset. The principle behind pipe bursting is to fracture the existing, deteriorating pipe displacing this into the surrounding ground while pulling the new replacement pipe into position without the need to excavate or remove the existing pipe.

Pipe bursting is most appropriate when a trenchless method of replacing an aging or damaged pipeline is required. Pipe bursting supplants the existing pipe forming a path for a new pipe as the existing pipe is displaced and because there’s no need to remove or dispose of the old pipe, project time and cost is minimised.