Underground works: another way to overcome obstacles

Underground works: another way to overcome obstacles

In a dense urban environment or when faced with serious topographical constraints, the transporting of effluents and fluids requires the use of trenchless installation techniques or the construction of main sewers or underground galleries.

Right from this development phase of the project, SADE is able to bring all its expertise in the areas of geo-technology and operational methods, aiming at safety and the best possible selection of technical options.
Project diversity, together with their geometry and hydrogeological context, requires customised solutions: SADE possesses a wide range of techniques implemented by experienced and highly specialised teams of experts that enable it to cover all aspects of underground works.

Pipe jacking

A technique of trenchless working, pipe jacking is used for crossing obstacles and laying pipes underground at great depths.

Particularly appreciated in built-up areas for greatly reducing disturbances caused by installations, this technique allows work to be carried out in rocky, pulverulent or loose soil with strong cohesiveness, and ensures quick completion of the operation and a significant reduction of ground surface restoration requirements.

The process is as follows:

  • construction of inlet and outlet pits,
  • excavation with a roadheader machine to cut through the earth,
  • jacking the pipes from the inlet pit as the line advances.


Thanks to its many years experience of this technique, SADE is able to respond effectively and rapidly to complex soil problems.

Horizontal and directional drilling

As excellent trenchless techniques, horizontal and directional drilling allow obstacles to be overcome (rivers, motorways, dwellings), floors and basements to be protected and greenhouse gas emissions to be reduced.

SADE operates an extensive range of drills for operations on different types of sites (urban or rural) and terrain (water table, obstacle, rocky ground, etc.), for diameters from Ø 25 to 1400mm.

Directional drilling is for laying different networks (drinking water, sewerage, heat, gas, optic fibre, etc) for diameters from 25mm to 560mm after the progressive sinking of a rod train into the earth.

For larger diameters (from Ø 219mm to 1,400mm) and more restrictive ground conditions (rocky and coarse alluvial soil), SADE uses trepan drilling to install pipes via inlet and outlet pits.

Microtunnelling

Microtunnelling is a pipe jacking solution available for the trenchless construction of underground networks. This technique is suitable for wastewater and drinking water systems as well as for energy and telecommunications networks. Diameters handled go from Ø 500mm to 2,500mm without any real limit on lengths, since several sections, straight or curved, with or without slope, can be joined together.

The microtunneller’s cutting wheel is adapted to the nature of the ground encountered on a case by case basis. The excavated material from the pipe jacking is brought to the surface by hydraulic spoil removal and treated on-site prior to land-fill. The guidance system can be by laser or gyroscope.

The microtunneller/pipeline unit is jacked forward in stages. The unit length of the pipes is generally 3 metres.

SADE’s fleet comprises about 10 machines covering all possible diameters. With its teams of engineers and technicians, SADE is recognised as one of the main players in this leading edge technology, as witness its records and the projects it is awarded.

The working diagram of a microtunneling worksite is the following:

Tunnelling

In the event of geological restrictions and design layouts with variable geometry, SADE overcomes these pipe laying difficulties by proposing tunnelling techniques for the transport of effluents.

The tunnel boring machine facilitates the construction of large diameter pipelines at great depth with very tight tolerances and negligible surface impact.

To carry out this type of operation, the excavation and final coating functions are coordinated as the line advances (in reinforced concrete segments).

Conventional galleries

Digging out galleries without using heavy mechanised resources is the so-called conventional method.
Relying on men and their know-how as regards digging and earthworks, analysis of the ground and sheeting systems, this process is still widely used. It often solves specific problems linked to the worksite’s environment.
 
When it is necessary, i.e. as an alternative to heavy mechanised resources, tunnelling using the conventional method requires equipment that is fast and compact.

SADE uses the conventional method of tunnelling whenever circumstances dictate.

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