News | March 16, 2001

Trenchless techniques in France prove their merits for water supply and sewer system repair construction

French engineering and construction firms are starting to develop innovative trenchless techniques for a variety of applications throughout the country.

Contents
Resin injection into service pipes
Service pipe lining
Ever-larger diameters for the swagelining technique
Cast iron, a material well suited to trenchless operations
Directional drilling for gravity-flow star systems
Concreting tunnel borer

With the development of new trenchless pipe laying techniques in France, the noise, dust, traffic disruption, accident risks and fall-off in commercial activity caused by civil works will soon be a thing of the past. Trenchless techniques now are being used to both build new networks and refurbish existing mains and service pipes.

The French Society for Trenchless Technology (FSTT), a scientific and technical association, was set up in 1990 in Montreuil. Its purpose is to promote trenchless techniques and provide training in their use with buried pipes and underground networks of all kinds. The FSTT is also involved in the national "Microtunnels" project, organized under the aegis of French ministries for infrastructure and research and a national project called "Rerau," involved in the study of refurbishment techniques for urban sewer systems.

Resin injection into service pipes
Faced with the problem of leaks at the tie-ins between service pipes and main sewers, the city of Lille in northern France called upon the Société des Eaux du Nord to develop simple, robust, low cost repair techniques.

An original sealing technique by injection, called Fillinsen, was developed using specially designed sleeves and a non-toxic resin. The Fillinsen sleeve comprises a stainless steel body fitted at both ends with highly extensible elastomer rings, capable of adapting to different service pipe diameters. It creates a long injection chamber covering the entire connection onto the main sewer and the downstream end of the service pipe.

With the help of video cameras, the sleeve is positioned in the main sewer at the connection point. A plug is then propelled into position using a set of rods, and the sleeve and plug are inflated to create a pressurized chamber (0.6 bar). Liquid resin is then injected into the service pipe via the sleeve. At leakage points, the raised pressure causes the resin to penetrate the ground where it polymerizes. Once the most downstream leak has been sealed, the mixture continues to fill the pipe until it reaches the most distant leakage point.

The resin used is particularly well suited to this procedure. Its composition can be adjusted to lengthen the polymerization time (generally 90 seconds for filling, compared to 30 seconds with conventional treatment methods) to avoid obstructing the service pipes during injection.

Straight service pipe assemblies can be treated using the Minipacksen sleeve. Thanks to its extendible elastomer end rings, the tool is highly compact (around ten inches in length), with a small diameter (4.5 in.) adaptable to different service pipe sizes. This is used to seal service pipe leakage points by injection (with rod propulsion) via very small manholes. (Return to top)

Service pipe lining
BARRIQUAND, a French company based in Amiens, north of Paris, has developed the Sikaliner lining technique for sewer service pipes. A liner impregnated with epoxy resin is inserted into the pipe via a manhole by means of a winching system. This liner, five millimeters thick, is made of polyester felt reinforced with glass fiber, covered on the outside by an impermeable polyethylene film. It is pressed against the pipe walls by inflating an inner tube which runs through the middle. The pressure is maintained for around twelve hours until the cold polymerization reaction is completed. The liner extremities are then cut and trimmed in the main sewer using a remote-controlled robot inserted through a manhole. (Return to top)

Ever-larger diameters for the swagelining technique
In 1993, the French company SADE in Paris won an environmental medal for its original service pipe refurbishment technique, called Extractor, for use on water supply mains. Using this technique, lead pipes can be replaced with new high or low-density polyethylene pipes without any trench digging. Moreover, the old lead pipes are removed from the ground.

SADE employs a range of trenchless techniques. For several years now, it has been using its Swagelining technique, patented by British Gas, for pipe lining operations. With this system, old pipes requiring refurbishment are lined with pre-deformed high-density polyethylene tubes. The elasticity and shape memory of the polyethylene ensure that the new tubes fit snugly against the inner walls of the old pipes without the need for an annular vacuum. The tube is first heated to 176°F, and its diameter is reduced by between 10 and 20% by passing it through a conical die. It is then drawn out under a constant tensile load to maintain the temporary diameter with an elongation of around four percent. Once released, the tube returns to its initial diameter within twenty-four hours.

For each pipe diameter, SADE designs and builds a machine, which heats the tube and reduces its diameter. After successively pioneering diameters of two feet and then thirty-two inches in France, the company recently achieved a first in Portugal with a twenty-inch diameter pipe. The lining operation, performed in a refinery, was completed without shutting down the plant's activities. This technique can be used to refurbish pipes made of cast iron, steel, reinforced concrete, and asbestos cement, operating under pressure or by gravity. (Return to top)

Cast iron, a material well suited to trenchless operations
The French company Pont-à-Mousson in Nancy now produces ductile cast iron pipes well suited to the needs of network designers and builders. Cast iron pipes, capable of withstanding heavy mechanical loads, can be used for pipe diameters of between two and twenty inches without risk of deformation or elongation.

To renew a gray cast iron pipe section, place-for-place laying techniques were used in a residential area of Sucy-en-Brie near Paris by Pont-à-Mousson and a second firm, Ile de France Canalisations. A pipeleg measuring 485 feet, in two sections, was replaced in five successive drawing operations. One straight leg, measuring 157 feet in length, was drawn through in one go.

At Chatel-sur-Moselle, in the Vosges region of eastern France, the Technoform company, a specialist in directional drilling, laid 690 feet of 5.9 inch ductile cast iron piping under the Moselle river and the Canal de l'Est. The entire pipe string was drawn through in less than three hours.

For these operations, the outer pipe surface was protected by a layer of zinc covered by an extruded polyethylene coating. This smooth coating protects the pipe and reduces friction when it is drawn through the ground. The self-healing zinc underlayer provides corrosion protection.

The pipe connections are equipped with special locked joints which prevent any risk of disjointing under the tensile loads applied during drawing. This system is also able to withstand major angular deviations, enabling the locked pipe string to follow a curving pipe route without any problem. (Return to top)

Directional drilling for gravity-flow star systems
Used until now as a means to pass underneath obstacles (canals, rivers, railway lines), directional drilling is now increasingly used for the construction of urban water supply networks. Le Forage Directionnel, a company in Villebon that specializes in this field, has extended its use to the construction of gravity-fed sewer systems and sub-soil analyses. It is now possible to determine the exact composition of the ground encountered by a microborer advancing at a depth of about forty-nine feet for example.

A world first has been achieved at Athis-Mons in the Essonne region of France with the construction of a gravity-fed sewer system constructed entirely by directional drilling. This consists of a main sewer and its service pipes, a part of which is laid at a gradient of 0.5 percent. The construction of this system using conventional methods at a depth of twenty feet along the edge of a major trunk road would have been very difficult. In view of the danger, technical obstacles and high costs incurred, the directional drilling technique was preferred.

The company used access pits destined to become manholes to construct the "star" system, with service pipes connected directly at the manholes. This type of installation, made possible by directional drilling, does away with service pipe connections to the main sewer, thus eliminating the associated leakage risks and simplifying sewer system management. (Return to top)

Concreting tunnel borer
In the field of sewer construction, which represents 80 percent of its activity, the French company Devin Lemarchand Environnement (DLE) in Chavenay also uses trenchless techniques, working with micro borers for diameters less than four feet and standard borers for larger diameters.

In this field (from six to twelve feet), DLE has developed an original technology for which it has designed and built a special machine: the "concreting tunnel borer." Ready-mixed concrete is used daily to build the final structure. The following day, the tunnel borer builds on the work of the day before. Depending on the type of ground and the equipment configuration, the machine advances from thirteen to twenty feet each day. Metal forms are used to define the shape of the structure (circular or horse-shoe) and its appearance, while the borer thrust is transmitted via a set of five forms.

The forms for each concrete ring remain in place for one week until the concrete has acquired sufficient structural strength. After removal, the forms are then reused to build a new ring. This method can be used on urban sites, since no prefabricated segments are required and surface work sites are very small.

The system is competitive in terms of cost, especially for pipe lengths of less than 300 feet. DLE recently built a pipe with a nine foot diameter having a length of 476 feet, to take rainwater to a tank under the training pitch of the Stade de France soccer stadium north of Paris. It is currently completing a 918 foot pipe to collect rainwater and take it to a seven million cubic foot underground storage tank. DLE has so far built 23,000 linear feet of piping using this method.

French companies have developed considerable expertise in these techniques, and a growing number of local authorities now recognize their merits. A wide range of solutions are now available for the construction and refurbishment of water supply and sewer systems with minimum inconvenience to urban populations. (Return to top)

Source: French Technology Press Office. This article was prepared by Bernadette Lacaze, a technical freelance writer in Paris.

For more information, please contact the French Technology Press Office, One East Wacker Drive, Suite 3740, Chicago, IL 60601; Fax: 312-222-1237.

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