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Trenchless Technology

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Trenchless technology (TT), also called no-dig installation, is a new way of installing and renewing underground utility pipes without having to create a traditional surface open-cut or continuous trench. The term trenchless technology is actually a bit of a misnomer since a certain amount of surface excavation is required. However, trenchless technology is nowhere near as evasive as conventional open-cut trenching methods that create much more surface ground disturbance.

In an open-cut trench, a pipeline is directly installed along the length of the cut. The excavation of an open-cut trench accounts for only a fraction of the project's total cost, with backfilling, compaction, and reinstatement of the surface landscape accounting for almost 70 percent.[1] Other names that apply to open-cut trenching in construction are dig-and-install, dig-and-repair, and dig-and-replace. Trenchless technology differs from open-cut trenching because there is minimum surface excavation and no need to backfill or conduct ground reinstatement

Many types of trenchless technologies exist today, generally falling into one of two classifications: trenchless construction methods (TCM) and trenchless renewal methods (TCM). A trenchless construction method is any method used for all new utility and pipeline installations. Trenchless renewal methods refer to any method used for renewing, rehabilitating, or renovating existing pipelines and utility systems.[2]

Contents

[edit] History

Until very recently, open-trenching surface excavation was the only method used for new pipeline installation. However, over the last 25 years it became clear that little was known about existing pipelines or utility infrastructures that have been previously installed. Research was quickly undertaken to find ways to gather information on existing pipes and ducts often too small to be entered manually by service workers. One of the largest breakthroughs in this research was the development of closed circuit television in conjunction with remote control tools. With these technologies, the internal state and conditions of smaller pipelines could be easily inspected and then repaired. This led to a huge demand for the development of similar techniques. The need and adoption for trenchless technologies quickly emerged to meet the specific needs of different countries around the world. For example, micro-tunneling evolved in Japan out of a demand for more sewer systems in the country’s larger cities. In the U.K., where many of the cities had been built during the time of the Industrial Revolution, trenchless technologies were used to replace and fix aging sewers, water pipes and cast iron gas mains. In North America, another trenchless technology called horizontal direction drilling was developed from vertical steered oil well drilling. The technology was later adapted for the widespread purpose of constructing long pipelines for the oil industry. By 1986 Japanese, American, and European engineers banded together to officially categorize all of these techniques under the umbrella of trenchless technology.[3]

[edit] Process/Types

[edit] Trenchless Construction Methods

Trenchless construction methods (TCM) include all methods used in the installation of new utility systems below grade without direct installation in an open trench. TCM is also categorized according to work-entry required and worker-entry not required. The three most widely used applications that define trenchless construction methods include

[edit] Horizontal Earth Boring (HEB)

This is the mechanical excavation of a borehole that permits worker access. There are different types of techniques that fall under this method.

[edit] Horizontal auger boring (HAB)

This is a cost-saving technique for installing pipes crossing over a road, highway, or track. A steel casing gets jacked from a drive pit through the earth while discarding the spoil inside the encasement by means of a flight auger. The casing supports the spoil around it as the soil is being removed. A product pipe is then installed inside the casing and the surrounding annular space is filled with grout.

[edit] Microtunneling (MTBM)

This is used mostly for the installation of gravity pipelines such as sanitary and storm sewers. It requires a draft shaft for jacking pipe and an exit shaft for retrieving the equipment. This type of system also uses a laser-guided remote control system that allows accurate monitoring and adjusting as the work proceeds so the pipe can be installed on a precise line and grade. It was developed for pipes with a diameter of 36 inches (90 cm) or less but has since been adapted for use for larger pipe where remote control is necessary.

[edit] Horizontal directional drilling (HDD)

This method is used for the installation of pressure pipelines and cable conduits and involves the use of a steerable system to install both small- and large-diameter pipes. A small pilot hole is drilled along with the desired center of a proposed line. The pilot hole is then enlarged to a diameter that accommodates the pulling of the pipeline through the hole. With a steerable system, the drill bit is able to be tracked and steered as drilling occurs.

[edit] Pipe ramming (PR)

This is a method used to install utility systems for roads and railway crossings by using an air compressor to hammer steel casing through the earth from a closed- or open-end drive pit.

[edit] Compaction method (CM)

Also known as impact moling, this method is used mainly for the non-engineered installation of small-diameter road and street pipelines. A borehole is created by compressing the earth and then pushing or pulling the pipe through.

[edit] Pilot-tube microtunneling (PTMT)

Pilot-tube microtunneling is seen as an alternative to conventional microtunneling and combines the accuracy of microtunneling using a steering mechanism of a directional drill and spoil removal of an auger boring machine.

[edit] Pipe Jacking (PJ)

This is a method that allows workers to enter a borehole during the excavation and temporary pipe installation processes by using prefabricated pipe sections—it is used mostly in tunnel construction. New pipe sections are then jacked into place from a drive pit so that each section can be installed simultaneously as the excavation of the tunnel proceeds.

[edit] Utility Tunneling (UT)

Utility tunneling is a method that allows workers to enter the borehole during excavation as well as the temporary installation of pipes. It uses the same types of excavating equipment as pipe jacking but the temporary support structure placed at the excavation face is made of linear or steel rib plates with wooden lagging.

[edit] Trenchless Renewal Methods

Trenchless renewal methods (TRM) are still being developed and are mostly used to replace, repair, renovate, or upgrade an existing pipeline system. Most of the methods that fall under this category are also used to replace or enlarge existing pipes.

[edit] Cured-In-Place Pipe (CIPP)

This is a method that involves the insertion of a resin-impregnated fabric tube into an existing pipe by use of air or water inversion or winching. The water or air is used during the inversion process and steam or hot water is used for curing. Since the resin is pliable it is able fill up the surrounding crack areas, gaps, curves, and maneuver around pipe defects.

[edit] Underground Coatings and Linings (UCL)

This term refers to a renewal method of spraying a mortar lining or resin onto pipes using a remote control sprayer.

[edit] Sliplining (SL)

This is a method used for structural applications when existing pipes lack joint settlements or misalignments. A new pipe is inserted into the existing pipeline and the space in between the existing pipe and new pipe is grouted.

[edit] Modified Sliplining (MSL)

This methods involves the use of pipe sections and plastic strips installed in close-fit with existing pipes and grouting of the annular space. Three variations of the method include panel lining, spiral wound, and formed-in-place pipe.

[edit] In-line Replacment (ILR)

When the condition of pipes is beyond repair, this method is considered most appropriate. ILR represents three categories: pipe bursting, pipe removal or pipe eating, and pipe insertion. Pipe bursting is using a hammer to break apart old pipe and force the particles into the earth. The new pipe gets pushed into the old pipe’s place at the same time. Pneumatic pipe bursting, static pipe bursting, and hydraulic pipe bursting are all variations of this technique. Pipe insertion or expansion involves jacking a new pipe into place, usually a new rigid pipe made of clay or ductile iron. Pipe removal is performed with an HDD rig or HAB machine. The small pipe is broken into small pieces and taken out with a slurry or an auger.

[edit] Close-fit Pipe (CFP)

This is a trenchless pipeline removal method that reduces the cross-sectional area of a new pipe before installation. After placement, the pipeline expands into its original size and shape.

[edit] Localized Repairs (LOR) or Point Source Repair (PSR)

When local defects are found in an otherwise structurally sound pipeline, a local or point-specific repair is considered. Systems make use of remote-controlled resin injection to seal localized defects in pipes ranging from four to 24 inches (10 to 61 cm) in diameter.

[edit] Thermoformed Pipe (ThP)

This is the term used in North America to describe pipes that have a reduced cross-section by folding for insertion, which are then heated to thermoform them to conform to the dimensions of the host-pipe. This is a new form of renewal trenchless technology. The pipe is made of folded PVC or PE pipe.

[edit] Later Renewal (LR)

Service sewer laterals can use methods also used for renewal of mainlines. These include chemical grouting, cured-in-place, close-fit pipe, pipe bursting, and spray-on lining.

[edit] Sewer Manhole Renewal (SMR)

This is a method designed to prevent surface water flow or groundwater structural damage and protect surfaces from damage due to corrosive substances. If a renewal method is insufficient, replacement of a manhole is considered the best alternative. It is divided into the following methods: cementitious, cast-in-place, cured-in-place, and profile PVC.

[edit] References

  1. Nakafi, Mohammad and Gokhale B. Sanjiv. Trenchless Technology: Pipeline and Utility Design, Construction, and Renewal. McGraw-Hill Professional. 2004
  2. Nakafi, Mohammad and Gokhale B. Sanjiv. Trenchless Technology: Pipeline and Utility Design, Construction, and Renewal. McGraw-Hill Professional. 2004.
  3. Development of Trenchless Technology Systems. United Nations of Technology, Industry and Economics. 03-16-2009.
Petroleum Processes