Project Management Assistance (AMOET) for the supervision and monitoring of works
This project involves the injection of cement grout into the subgrade of the Champs du Buisson (Arrou) cutting in order to backfill the marl pits using grout injection. The aim of this work is to fill the existing voids beneath the railway platform to prevent the track bed from becoming prone to subsidence or even the formation of sinkholes.
This work, carried out from the platform, therefore involved the injection of barrier grout followed by backfill grout (gravity injections and pressure injections) from km 130+705 to km 130+841 (a total length of approximately 136 m). No remedial grouting was planned in this case.
The platform consists of two tracks: tracks V1 and V2, on which high-speed rail traffic runs. These electrified tracks are laid on a low-level earth embankment.
Following the pilot holes (drilled vertically to a depth of 6 m), the grouting boreholes were drilled from the side platforms at an angle ranging from 22° to 40° and a length ranging from 12 to 15 m, spaced 3.0 m apart, so as to cover the entire platform beneath the tracks. The total estimated volume of grout is 4,230 m³. The depths of the marl deposits were identified as being around 12 m.
TERRASOL was tasked with providing Project Management Assistance (AMOET) under the supervision of the MOEE and MOEG to monitor and ensure the smooth progress of the drilling and grouting works on the marl deposits identified beneath the LGV Atlantique platform at the Champs du Buisson excavation site in the municipality of Arrou.
Throughout the project, TERRASOL was responsible for ensuring full compliance with the contract specifications and requirements, as well as the quality and effectiveness of the platform treatment at the Champs du Buisson excavation site. TERRASOL was also required to take a proactive role in adapting the specifications based on findings during the works in order to optimise the quantities injected.
TERRASOL therefore began its assignment by supervising the detailed design work, reviewing the technical documents provided by the contractor awarded the contract (construction procedures, blasting plans, injection depths, material quality, etc.) and ensuring that the works complied with the specifications.
TERRASOL then oversaw the works by analysing the borehole logs, monitoring the volumes of backfill and treatment grout injected whilst ensuring compliance with the cessation criteria (volume thresholds, pressure thresholds, platform uplift thresholds), and reviewing the grout suitability tests, etc.
Following completion of the works in each zone, TERRASOL defined a programme of control boreholes and examined the results of the associated tests. Comparison of the post-treatment borehole data enabled a conclusion to be drawn regarding the effectiveness of the grout injection works in backfilling the marl pits.
Miscellaneous
- Cement grout injection for backfilling marl pits
- Estimated volume of grout for injection:
- VBarrage: 460 m³
- VBackfilling: 4,230 m³
- Treatment depth: P = 12 m
