London, Crossrail C298 Deep Dry Soil Mixing | Vibro | Keller UK

London, Crossrail C298 Deep Dry Soil Mixing

For this £1.4million scheme Keller installed around 4200 Deep Dry Soil Mixed (DDSM) columns to stabilise very soft clay and organic soil to support the safe construction of a 4.0m high retaining wall for the London Crossrail Plumstead Sidings project. The DDSM columns treated the in-situ materials to a depth of 5.0m, to achieve an unconfined compressive strength of 250kPa. The works were completed using two rigs and cement shuttles.

Deep Dry Soil Mixing (DDSM) treated the in-situ very soft alluvium and organic soil to give an unconfined compressive strength (UCS) of the columns of 250kPa. Nearly 4200 No. 5.0m long DDSM columns were formed to enhance the properties of the existing ground to provide the required bearing capacity and settlement control to support a 4.0m high reinforced soil retaining wall. Supporting the new rail sidings.

Under the supervision of the Principal Contractor, Balfour Beatty, Keller undertook an up-front programme of soil sampling and laboratory testing to enable optimisation of the column binder content and predict as-built properties of the treated soil. These tests confirmed a CEM II binder content of 190kg/m3 of mixed ground.

An extensive program of insitu testing, which included 128No. winged CPT and 2No. static load tests, validated the finished product .

The setting out of the columns were completed using GPS receptors on the rig. This provided a safe system of work by reducing the workforce requirement around the working rig and providing an accurate as-built position of the columns. The use of GPS also improved productivity by reducing set up time of the rig over each column. The specially adapted DDSM rigs are fitted with onboard compter control that ensures a consistent product is delivered while recording detailed construction records providing a robust QA process.

Systems:

  • 4164No. DDSM Columns installed—800mm diameter
  • 128No. CPT/Winged CPT completed to validate strngth requirement for the scheme.
  • 2No. Static Load tests completed to validate settlement criteria of the works.

Client: Crossrail Ltd

Contractor: Balfour Beatty Construction Services

Engineer: C122 (Arup/Atkins Joint Venture)

Year of execution: 2014

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