Autoripage® of 6000 tonne box structure across railway
The Radlett Strategic Rail Freight Interchange (SRFI) development involves the construction of a new rail to road freight depot on the site of the former Radlett Aerodrome near St Albans. The project requires the design of a new rail connection to the Midlands Main Line (MML), including an embankment to support the new rail chord, and an intersection bridge (underbridge) allowing the new rail chord to pass underneath the four tracks of the MML.
VolkerFitzpatrick adopted Freyssinet’s Autoripage® technique to slide the intersection bridge into position underneath the existing railway during the rail blockade over Christmas 2024.
|
Autoripage® is a patented method developed by Freyssinet. This innovative method involves casting the underpass ‘offline’ on a guiding raft adjacent to the operational railway. Using bentonite liquid clay as a lubricant, the structure is slid into its final position. Once in place, backfilling is carried out to restore the route for traffic. The Autoripage® technique reduces disruption and improves safety, as it separates the construction activity from the operational railway. The method is particularly beneficial for rail and road crossings.
For the Radlett project, the sliding operation was successfully completed in 12.5 hours, three hours ahead of the original schedule.
Scope of work by Freyssinet included:
- Design of temporary guiding raft and pushing slab.
- Design and supply of all necessary components for Autoripage® including the anchorage blocks, passive/active deviators, steel inserts, strands, Ipalen plate, grease, bentonite etc.
- Installation of the strands for jacking operation.
- Design, supply and installation of the hydraulic jacking system.
- Operation of the sliding operation.
- Injection of bentonite during the sliding operation.
- Injection of cementitious grout into the omega channel underneath the structure base slab to expel the bentonite.
Key Project Figures
| Item | Details |
| Size of the permanent structure | 61.38m (L) x 16.55m (W) |
| Size of the temporary guiding raft | 79.60m (L) x 17.37m (W) |
| Total weight of permanent structure for sliding | 6000 Tonne |
| Sliding distance | 62.5m |
| Strand number | 46 nos. per cable & 23 nos. per jack |
| Hydraulic jack details | 12 nos. x Strand Jack H-400 |
| Hydraulic pump details | 6 nos. x PA-4-30 |
| Blockade period | 21 December 2024 at 03:00 to 30 December 2024 at 04:00 |
| Date of test slide | 20 December 2024 |
| Date of main slide | Start: 22 December 2024 at 16:58 Finish: 23 December 2024 at 05:20 |
| Duration of slide | 12 hr 22 mins |
| Peak sliding speed | ~ 15m/hr |
| Average sliding speed | ~ 5m/hr |
Freyssinet Radlett Box Slide – December 2024