With the total rehabilitation of an accessible sewer main in Boulogne and a worksite combining chemistry and public works.
Seine Ouest Assainissement, a subsidiary jointly owned by Veolia and SADE, has been awarded the wastewater treatment public-service outsourcing contract for GPSO (Grand Paris Seine Ouest, i.e. Greater Paris West Seine) up to the end of 2027. SOA’s contract covers approx. 60 replacement and/or rehabilitation operations on systems in 8 local towns and villages. One of these is the consolidation and rehabilitation of a section in Passage des Abondances (Boulogne-Billancourt).
Did you say “accessibility”?
Until now, the design & construction operations carried out for GPSO practically only involved inaccessible facilities. But in this case, the teams are rehabilitating, from the inside and over a 160m stretch, an accessible facility (T180), going under buildings, made from both masonry (100m) and concrete components (60m). SADE Special Works was selected for this mission.
A multi-technique worksite
Though the concrete segment only involves circular crack repairs, the masonry section requires heavy, technical work. To consolidate this section, bentonite/cement mix grout is injected into 66 points each featuring 4 tubes and a duct (i.e. 330 ∅ 40 drill holes). This mixture is injected at a maximum pressure of 2 bar at a rate of 10l/minute, in runs of no more than 225l and as much as the terrain required. To protect it from water damage, H2S-resistant fibre-reinforced mortar will be sprayed onto the arch, abutments and gutter.
The bentonite-cement grout injected must be 28-day 8mpa strength. This means it must be very precisely formulated and every batch produced by the injection plant up on the surface checked. The fresh grout’s viscosity is checked by testing the flow rate of a sample of 1 litre through a cone, which must fall in the 35-40” range. Its density, which is measured using a Fann scale, must be precisely 1.45 and its exudation test results must be below 3% after 2 hours. Samples of each batch are also kept to carry out tests on hardened grout. In addition to self-inspection, when each injection phase begins, suitability tests were carried out by an external firm to check both equipment and grout formulation.
A hi-tech injection plant
The injection plant is almost entirely automated and was designed and manufactured in STS’ workshops. A wide range of automated systems, sensors, counterweights and other flow meters are used to precisely check the quantities of water and cement in each batch, and the pressure and flow rate for simultaneous injection into 2 lines, plus post-discharge wastewater treatment. The only manual operation left is adding in the bentonite. This plant is quiet enough not to disturb locals living near this 10-week worksite, which kept 7 SADE staff busy.