United Kingdom Society for Trenchless Technology: UKSTT - Pipe-Cables Installation Techniques
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Click here to view all UKSTT Members involved with Impact Moling.
Impact moling is a technique in which a percussive mole (soil displacement hammer) is launched from an excavation to displace the soil and form a bore. The new conduit is normally drawn in behind the mole or pulled back into the bore using the hammers reverse action. Pneumatically driven moles, in which the soil is displaced by the action of a percussive piston, have been developed in the range 30 - 180mm diameter for a single operation, with repetitive multiple passes to achieve 200 - 250mm diameter.
Utility companies and their contractors use moles on a daily basis to lay new or replace existing services usually up to about 63mm diameter. However, larger bores are also common laying pipes up to 180mm, with lengths sometimes exceeding 40m.
Click here to view all UKSTT Members involved with Pipe Ramming.
Pipe ramming is a simple technique utilising a pneumatic hammer to drive steel casings through the ground from one pit to another. Rams of pipes up to and over 2m diameter and exceeding 70m in length have been achieved.
Basic operation is as follows:
Click here to view all UKSTT Members involved with Auger Boring & Thrust Boring.
Click here to view all UKSTT Members involved with Pipe Jacking.
Click here to view all UKSTT Members involved with Micro Tunnelling.
Microtunnelling is used here as a general term to describe remotely controlled mechanical tunnelling systems where the spoil is removed from the cutting head within the new pipeline which is advanced by pipe jacking.Microtunnelling machines have now been developed to work from drive shafts in almost all types of ground conditions. However, it is essential to know what these conditions are likely to be as they will determine the type of machine to be used, the cutting head, the spoil removal system, and the jacking forces likely to be required.
The cutting head has to be carefully selected to deal with the expected ground conditions, with the appropriate cutting tools and crushing devices for the range of gravels, sands, silts, and clays.
The only excavating required from the service is for drive and reception shafts. Spoil may be removed from the face by an auger running through the newly installed pipeline to a skip in the base of the drive shaft.
Alternatively, water or bentonite may be used to convert the soil into slurry at the cutting face. The slurry is then pumped to the surface where the solids are separated before disposal. Both systems provide face support by mechanical earth pressure balance. Slurry pressure at the face can also be used to combat external ground water.
With some systems, control is exercised automatically but microtunnelling machines are generally operated from a control console in the cabin at the surface. The location and orientation of the machine is continually monitored, usually by means of a laser guidance system. Accuracy in driving usually depends on the skill and experience of the operator, especially in varying ground conditions.
Microtunnelling is used extensively for sewerage work where surface disruption has to be minimised. It provides the necessary degree of accuracy in gravity lines. If a scheme is designed with a trenchless solution in mind the drive and reception shafts can be located where they can become manholes in the finished scheme. They may also be sited to minimise disturbance of the highway and traffic disruption during construction.
Considerable advances have been made in recent years. Machines are now available to drive 100m or more in soft ground for sizes of 100mm diameter upwards, from drive shafts of less than 3m diameter. The use of laser guidance control systems and computer monitoring, allied to steering capability, has enabled a high degree of accuracy to be achieved, typically within +/-25mm. It is often the case that microtunnelled sewers are installed to a higher degree of accuracy than those laid in conventional trenches and the pipes are more evenly stressed.
With the development of microtunnelling, both concrete and clay pipes have been designed with jacking in mind. Pipes in all conventional materials are produced with in-wall joints and in shorter lengths to enable smaller drive shafts to be used, thus reducing excavation volumes and road occupancy.
Microtunnelling systems have been developed in which temporary steel tubes are jacked in and removed at the next manhole position, the new pipeline following in the established bore.
Much attention has been given to reducing the impact of pipeline construction on the environment. Often, the only indication on the surface is the presence of a control container with a hoist for lowering pipes into the drive shaft. Noise levels and traffic disruption are minimised. Both the extent and duration of any road occupancy is often a small fraction of that required if a trenched method of construction had been adopted.
Information and schematics courtesy of ISTT
Click here to view all UKSTT Members involved with Guided Rod Pushing.
Click here to view all UKSTT Members involved with Guided Boring & Directional Drilling.
Horizontal Directional Drilling (Guided Boring) is ideal for the underground installation of gas, electric, water, telecommunication or soil remediation lines - without excavation or trenching. Horizontal directional drilling ensures minimal or no environmental disruption and is an excellent choice for installations in diverse rock and soil conditions. Directional underground drilling can be used for many different types of jobs, including road, landscape and river crossings.
Horizontal directional drilling units install utilities by pilot boring underground. The system uses a removable drill head matched to soil conditions by the operator and a series of drill stems to push and rotate the head. Once the pilot bore is completed, a reamer/backreamer is attached to the drill stem string and pulled back -- enlarging the bore wall to comfortably accommodate the product wire, conduit or pipe that is subsequently pulled into place.
Pipes, Ducts or Cables of up to 1200mm diameter have been installed using this method in lengths exceeding 1.5km. Small utility pipe works utilising this method are carried out day to day throughout the UK and indeed the world.
Click here to view all UKSTT Members involved with Rock Boring.
Rocks can be classified in strength as:
Hardest surface rocks being max 40,000 psi (270 Mpa)
The key to successful "Rock Drilling" is by Engineering, Planning and Selection of the correct drilling package knowing the particular ground conditions / rock strengths etc.
We can still use the "Directional Drilling m/c" but with certain modifications / special tooling, comprising of:Drill Rods as well as having a large enough bore for the mud flow should also be have enough strength for the rotary torque and the pull back of the Hole Openers /pipe weight.
The above perimeters of "Mud Flow" and "Drill Rod Size" therefore dictates the size of Horizontal Drilling M/c to utilise.
Selection of the Correct Drilling Muds, flow rates, Mud Cleaning (Recycling) systems are all essential for bore hole cleaning and penetration rates.
Guidance of the "Pilot Bore" is either a "walk-over" or remote "wire line" tracking system as is normally used with Horizontal Direction Drilling.
Click here to view all UKSTT Members involved with Cable Pulling.
Cable pulling is the oldest method of inserting a cable into existing ducting. This entails feeding a winch rope through the ducting and attaching it to the cable with a compression sleeve or sock. As the cable is winched into the ducting the sock tightens its grip on the cable. On larger cables a cable pusher is used to assist the winch and thus reduce tension in the cable.
Click here to view all UKSTT Members involved with Cable Blow In Systems.
Cable blowing is used to insert relatively small diameter, light weight electric or fibre optic cables into existing ducting. Compressed air is introduced into the duct and the velocity of the air moves the cable. Small parachutes may be fitted to the cable to improve the insertion speed.
It is possible to purpose design the duct with a low friction bore to minimise possible damage to the cable and improve installation. This is particularly relevant to fibre optic cables.