Difficulties in Jetting Inside a Underground Station in Paris Sand Layers-Paper

Paper

Pdf Summary

The EOLE project extends Paris’s RER E line and includes construction of Porte Maillot station. This paper describes jet grouting for the station’s underground section, where columns were installed in sand to support staged excavation while protecting nearby buildings.<br /><br />Work took place in confined, low-headroom pilot tunnels, with grout equipment at the surface and spoil requiring transport through a 21 m shaft and along pipelines up to 280 m. Delayed groundwater drawdown prompted construction of higher pilot tunnels so jet grouting could begin sooner.<br /><br />During production, spoil removal became unreliable: hose pumps lost suction, pipelines blocked, and platforms flooded. The cause was small pieces of lignite encountered at certain depths. Once broken up by jetting, the dry, absorbent material took water from the spoil, thickening it during pumping and contributing to blockages.<br /><br />Larger temporary screens captured much of the lignite and reduced blockages, but did not resolve the problem. The team then trialled Bentocryl 86, a polymer deflocculant commonly used in bentonite slurries. Added to the grout mix, it improved spoil fluidity and pump performance. The adopted dosage maintained the required grout strength and enabled one pump to move spoil to the surface.<br /><br />The project demonstrates how geological conditions can affect spoil handling in underground jet grouting. A combination of filtration and a tailored polymer additive overcame the lignite-related pumping difficulties and helped limit further delays.

Keywords

EOLE project

Porte Maillot station

jet grouting

underground excavation

pilot tunnels

groundwater drawdown

lignite

spoil removal

Bentocryl 86

Paris RER E