Difficulties in Jetting Inside a Underground Station in Paris Sand Layers-PPT Presentation

PPT Presentation

Pdf Summary

The Porte Maillot station, part of the western extension of Paris’s RER E line, is being built in a congested urban area across four geological horizons. Its 225 m length combines open-air construction with a 70 m underground section. Because the groundwater level needed to be lowered before excavation, two elevated pilot tunnels were constructed to allow jet grouting to begin earlier.<br /><br />The grouting program comprised 351 columns, mostly 1.70 m in diameter, with a required minimum 28-day strength of 5 MPa. Work took place inside the pilot tunnels, where spoil had to be pumped up to 280 m, including 21 m vertically.<br /><br />After several weeks, spoil removal became problematic: pumps struggled to draw in the material, pipelines blocked, and the work platform flooded. Investigation identified unexpected lignite fragments in the spoil, which were light, stone-like particles that impeded pumping.<br /><br />The team installed additional filters and temporary screens ahead of pump suction. These captured much of the lignite and reduced blockages. To improve spoil fluidity further, they trialled Bentocryl 86, a deflocculating polymer, in the grout mix. The adopted mix improved fluidity and reduced pump pressure and blockages without compromising spoil strength; density remained above the required minimum. Ultimately, a single peristaltic pump could convey spoil to the surface.<br /><br />The project demonstrates how filtration and grout-mix adjustment can address unexpected geological conditions and maintain jet-grouting operations in a confined underground environment.

Keywords

Porte Maillot station

Paris RER E extension

jet grouting

groundwater lowering

pilot tunnels

grout spoil pumping

lignite fragments

Bentocryl 86

filtration screens

underground construction