Trenchless Technology is the science of installing, repairing or renewing underground pipes, ducts and cables using techniques that minimises or eliminates the need for excavation. The use of such techniques can reduce environmental impact, social costs and at the same time provide economic alternatives to traditional open cut methods of installation, renewal or repair.
TRENCHLESS TECHNIQUES: PIGGING, POWER WINCHING, AIR SCOURING, RACK FEED BORING, HIGH PRESSURE WATER JETTING
Essential to the success of such methods are training, planning, material and equipment choice. Trenchless techniques themselves can be broken down into three areas:
- repair and renovation
- new installation
Repair and renovation method includes: cleaning, localised repair techniques and lining techniques. The cleaning method includes: high pressure water jetting, specialist cutting equipment, power winching, drag scraping, pigging, air scouring and rack feed boring.
LOCALISED REPAIR TECHNIQUES: STABILISATION TECHNIQUES, CIPP PATCH REPAIR, CHEMICAL STABILISATION, STRUCTURAL PIPE REROUNDING, REPAIR SYSTEMS
Repair systems are used to address localised service problems or structural defects within a pipeline. The methods of localised repairs can be grouped as stabilisation or structural repair systems. The following sections describe a number of repair systems using trenchless technologies. In general, a stabilisation technique will address a localised problem, such as infiltration, without adding to the structural integrity of the pipeline. Typically, stabilisation techniques include chemical stabilisation, joint sealing and resin injection although in some circumstances the latter can also be classed as a structural repair. By definition, a defect addressed by a structural repair method will improve the structural integrity of a pipeline. Typical structural repair techniques include CIPP patch repair, robotic repairs and pipe re rounding. Localised repair techniques include: chemical stabilisation, joint sealing & testing, resin injection systems, patch repair systems, robotic repair systems, rerounding and lateral cutting. Localised repair techniques include:
CHEMICAL STABILISATION: SEWER REPAIR SYSTEM, FILL AND DRAIN TECHNIQUES, DRAINAGE SYSTEMS, SODIUM SILICATE
Renovation of a pipeline and ancillary features by sealing, between two access points by the chemical reaction of added compounds to the surrounding ground. The sealing of drainage systems can be achieved by chemical stabilisation 'fill and drain' techniques, which treat the main sewer, branches and manholes in one operation. Originating in Hungary, the system has been developed and is used quite widely as a 'non-destructive' sewer repair system. The section to be sealed is isolated and then filled from a manhole with an environmentally safe chemical solution (usually sodium silicate). After a predetermined interval to allow the chemical to permeate through leaking joints and cracks, the solution is pumped out quickly. The section is then filled with a second proprietary chemical solution, which reacts with the residue of the first chemical to form a waterproof membrane. The second chemical is then pumped out and the pipe is cleaned to remove any residues. The chemical reaction between the two solutions turns the material surrounding manholes and pipes into an impermeable mass, almost a weak concrete, around points of leakage. Due to the scale of plant requirements and the volumes of materials needed, these systems are more economical for large-scale leakage control projects than the treatment of isolated lengths. The greatest advantage of the method is to treat leaks throughout the whole system in a single operation.
JOINT SEALING & TESTING: POLYURETHANE RESIN GROUT
The testing and sealing of defective pipe joints with a grout injection using a packer, all activities being from a single process. A common method of sealing leaking joints in gravity pipelines is to use a packer, which combines the functions of leak testing and grout injection. Joint testing and sealing may or may not be 'localised', depending on how many joints fail. A packer with inflatable end elements is positioned across a pipe joint and pressurised to isolate the joint. Air or water pressure is then applied to the centre section of the packer and the rate of pressure loss through the joint is measured. If the loss exceeds a specified limit, a sealing resin compound is injected into the joint through the packer and the joint is re-tested. The packer design varies, using either a two-part acrylic grout or a water-active polyurethane resin grout. The grout combines with the ground around the leaking joint to form an impermeable mass, preventing leaks and enhancing structural stability. Polyurethane resin grouts are hydrophobic and react either with free water in the soil or with a water solution injected through the packer at the same time as the grout. Generally, a ratio of 1 part grout to 8 parts water is recommended for pipe sealing, variations creating products of different strengths.