S.A.R. wastewater effluent
Restoration of a main sewer by contact grouting
A monitoring survey of the SAR (the Sèvres -Achères-Rueil branch main sewer, 3.75m diameter) revealed evidence of substantial damage. Soletanche Bachy was contracted by SIAAP (the wastewater treatment authority for the Paris area) to carry out the contact grouting work to renovate the upstream part of the pipe. The work involved some two kilometres of the structure, located in a residential district of Rueil-Malmaison, a Paris suburb.
Contact grouting is carried out to fill the voids between the masonry and the soil (which in this case was either alluvia or Senonian chalk, depending on the zones). The grouting also produces a regeneration effect, through local treatment of the masonry and the soil in direct contact with the structure when there is high porosity. The grouting design was based on fans of 8 grout holes spread over 360° and at intervals of 1.25m, thereby producing a grid of 0.54 grout holes per square meter. The holes were drilled through the masonry, to a depth of about 60 to 70cm and the grout injected at low pressure in the "open holes". Grouting is carried out in two series of injections, if required, at 48 hours of interval. The acquisition and injection settings control system was driven by SPICE, Soletanche Bachy in-house developed software.
The injection work was carried out within the sewer, at a depth of 70m underground. The sewer was first emptied of all water, which meant deviating 320,000m3 of wastewater and installing a duct within the SAR to carry the 20,000m3 of wastewater which could not be deviated to the Achères plant. 8,000 grouting points, spread over 4 separate zones with a total length of 1,324 metres, were drilled using pneumatic hammer drills. 3 work sites were needed for installing the grouting plants and the grouting pumps (soundproofed) as near as possible to the injection points, some of which, however, were over a kilometre from the pumps. This meant that a fluidifying agent had to be added to bring down grout viscosity and prevent blockage of the grout lines.
Grouting involves the injection of a pumpable product (slurry), which will subsequently stiffen, into the soil or into man-made material (masonry), in order to consolidate the soil or structure or make it impermeable, through filling all the voids it contains. The slurry can fill the voids in the ground, the cracks within rock, solution cavities (it is then referred to as fissure and permeation grouting) and/or displace the surrounding soils through a bottom-up process or by fracturing (compaction grouting or solid injection - see the section on the subject - and strain injection). Grouting with soil displacement may be used to prevent potential damage to the structure brought about by excavations (galleries and tunnels, major urban excavations, etc.) and this is called compensation grouting (see the relevant section).
These works are carried out to reinforce foundations that have degraded with time or have been damaged by events. Where a structure is to be subjected to higher loads or forces than it was originally designed for, underpinning of the foundations is often required as part of its upgrade.
Soletanche Bachy group is very active in sanitation engineering
Voyage au coeur de l'ingénierie de pointe
Find out more about our expertise by: