Drump Road, Redruth Jet Grouting | Piling Contractors | Keller UK

Drump Road, Redruth Jet Grouting

Network Rail identified an abandoned mine shaft near to live London-Penzance Railway line.

It was decided that the best way to treat and stabilise the ground was jet grouting of the shaft and the soils surrounding it.

Utilising a 380 hour blockade of the railway Keller successfully installed 112No 1.6m diameter Jet Grout columns to form a cap and plug within the shaft thus stabilising the ground. Columns varied between 4 and 8m in length and were constructed within a very demanding programme of works.

The London to Penzance railway line provides a vital artery to the South West counties in the UK.  It was imperative the works including the preparation and reinstatement, were started and completed within the predetermined blockade period.

A remedial solution had been conceived by Network Rail and Ove Arup, however involvement from Keller developed the use of jet grouting as a viable alternative to other grouting solutions and piling.

Utilising a line blockade already in place for refurbishment of the Hayle Viaduct provided Network Rail an opportunity to carry out the works. Through discussions with Balfour Beatty ARUP and Network Rail and listening to their requirements, Keller were able to devise and implement a jet grouting, ground improvement solution.

The ground conditions were Made Ground (backfilled gravels mixed with Clay). This was overlaying weathered rock and then competent mudstone. The design accepted that full diameter columns may not be formed in the competent mudtone below 4m but that the jet grouting would exploit and grout the fissures and discontinuities. Full diameter columns above 4m were required.

The scope of works, advanced planning, mobilisation to site and construction were carried out under a very tight programme given the fixed dates of the blockade period. Steering meetings were held every 24hours between Keller / Balfour Beatty / ARUP / Network Rail to solve problems immediately. The jet grouting works were carried out working on a 24/7 basis.

One of the main risks during the works was the collapse of the sollar cap in the mine shaft during the operations. Given this risk had been ientified early a reinforced concrete slab was constructed to span the working area. This slab formed part of the permanent works after the jetting. Equally the jet grouting installation sequence was controlled to ensure the mass of the rig was supported on previously grouted columns.

3No trial columns were constructed prior to the main works. Additionally 4No working trial columns were carried out to measure column diameter during the constrution phase. The strength of the soilcrete specified by ARUP was >0.5N/mm2. Keller achieved an average soilcrete strength of 5N/mm2

System: Soilcrete Jet Grouting
Bulk Grouting of voided ground

Client: Network Rail

Contractor: Balfour Beatty Rail Division

Engineer: Ove ARUP & Partners


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