TRENCHLESS PIPE INSTALLATION
The method of forming a bore, usually from a drive pit, using a rotating cutting head is called the Auger boring method. Soil is removed back to the drive pit by helically wound auger flights rotating in a steel casing. The equipment may have limited steering capability. Guided Auger boring is the term applied to Auger boring systems which are similar to microtunneling, but with the guidance mechanism actuator sited in the drive shaft (e.g. a hydraulic wrench which turns a steel casing with an asymmetric face at the cutting head). The term may also be applied to those Auger boring systems with rudimentary articulation of the casing near the cutting head activated by the rods from the drive pit. The advantages of this tunneling system are that it causes little or no disruption to soil surface and no disruption to traffic. Its limitations include a very rudimentary steering system, thorough site investigations required and large boulders or very soft ground can cause problems.
HORIZONTAL DIRECTIONAL DRILLING METHOD (HDD)
The HDD method contains impact support and is called the Grundodrill technique. It enables trenchless installations up to 500 m length. The spectrum of application includes all pipe construction measures within the bounds of gas, district heating and drinking water supply, the installation of pressure lines for sewers as well as cable protection pipes for television or telephone cables, traffic routing systems, emergency call boxes or low, medium, high voltage and optical fibre cables. The HDD method is extremely protective towards the environment and causes no ecological damage at all. There are several reasons for the application of the directional technique in central town areas. They mainly concern the construction costs, construction periods, permission procedures, soil displacement, surface restoration and the traffic, compared to open trenching methods. The normal course taken by the drilling operation includes: planning, preliminary survey, selecting the drilling units and drilling tools, pilot bore and detection, backreaming(s) or upsizing bore(s) and pulling in the pipe. To overcome mechanical soil resistance high thrust and tension forces are required. The application of Bentonite might relieve the pilot bore and the pipe traction and provide the ability to steer in difficult soil qualities up to soil grade 5 or even 6. The HDD method is advantageous because surfaces worth conserving are neither broken up nor damaged, restoration and repair are not required, which leads to high economical advantages, low social costs because detours are avoided, short equipping as well as drilling and construction times, economic for river crossings, supported by the dynamic impact of the striking mechanism, the propulsion and ability to steer are improved in soil qualities of up to grade 5 and 6, it is an acknowledged procedure and pulling force measurement and position determination are possible.
PIPE JACKING TECHNIQUE
Pipe jacking, generally referred to in the smaller diameters as microtunneling, is a technique for installing underground pipelines, ducts and culverts. Powerful hydraulic jacks are used to push specially designed pipes through the ground behind a shield and at the same time, excavation takes place within the shield. The method provides a flexible, structural, watertight, finished pipeline as the tunnel is excavated. Practical engineering considerations and economics may impose restrictions. A number of excavation systems are available including manual, mechanical and remote control. Pipes in the range of 150mm to 3000mm can be installed. Excavation methods are either manual or machine excavation. To install a pipeline thrust and reception pits are constructed, usually at manhole positions. The dimension and construction of a thrust pit may vary according to the specific requirements. Mechanised excavation may require larger pits than hand excavated drives, although pipe jacking can be carried out from small shafts to meet special site circumstances.
A thrust wall is constructed to provide a reaction against the jack. High-pressure jacks provide the substantial forces required for jacking concrete pipes.
SOIL DISPLACEMENT METHOD
The soil displacement method is a method for underground pipe installation. A displacement hammer, driven by pneumatics, creates a cavity underground, ready for pulling in short or long pipes made of plastic and metal, preferably without socket ends, up to DN 200, but also any type of cable in drill lengths up to 40 m (depending on the soil quality). This allows trenchless traffic route crossings, private service line installations, the preparation of anchoring, bypassing obstacles and supporting further measures. This is a better method to be used in rocky soils because the complete impact capacity can first be concentrated on the multi-cutter cone.
DRY BORING METHOD
This is a combination of the soil displacement method with steered displacement hammer. Its advantages include: surfaces worth conserving are neither broken up nor damaged, economic advantages such as low social costs because detours, half-sided barriers and set up of signal facilities are avoided, it is suitable for longer private connections and traffic route crossings, no residential problems when installing private connections, short set up and propulsion time required, small pits used for short and long pipes without socket ends to 200 mm displaceable pipe diameter.
Microtunneling is a process that uses a remotely controlled Microtunnel Boring Machine (MTBM) combined with the pipe jacking technique to directly install product pipelines underground in a single pass. This process avoids the need to have long stretches of open trench for pipe laying, which causes extreme disruption to the community. Typical microtunnel equipment spread consists of an MTBM matched to the expected subsurface conditions and the pipe diameter to be installed, a hydraulic jacking system to pipejack the pipeline, a closed loop slurry system to remove the excavated tunnel spoil, a slurry cleaning system to remove the spoil from the slurry water, a lubrication system to lubricate the exterior of the pipeline during installation, a guidance system to provide installation accuracy, an electrical supply and distribution system to power all of the above equipment.