Down Leisure Centre, Downpatrick | Piling Contractors | Keller UK

Down Leisure Centre, Downpatrick

For this £0.5m scheme, Keller installed approx. 1000. No. wet soil mix (WSM) columns to depths of between 2m and 7m to aid in the construction of the new swimming pool and associated plant for the new Down Leisure Centre, Downpatrick, Northern Ireland.  All of the WSM columns were 1.5m in diameter and overlapped by 0.15 and 0.3m to achieve a full mass stabilized block.

A Wet Soil Mixing solution was proposed for this site by Keller to aid in the safe construction of the new swimming pool and associated pumping machinery for the new Down Leisure Centre, Downpatrick.  A total of 585 No. columns treated the ground to 2m depth with a further 390 No. columns treating the ground to 7m depth. 

Ground conditions beneath the site were especially poor, described as very soft clayey organic marine silts with pockets of peat.  SPTs of 0 were common to depths of 18m bgl.

The soil mixing solution was essential because the swimming pool  required excavations down to approximately 5m depth for the pumping equipment.  Sufficient passive resistance could not be generated from the weak silts, ruling out traditional techniques.  A mass stabilised block was proposed as the best option with Keller in early dialogue with both the contractor and their appointed designer.

The target undrained shear strength for the mixed soil was 100kPa.  Before carrying out detailed design, Keller undertook laboratory mixing trials to determine the necessary grout content to ensure we could achieve the target strength.

Keller’s thorough QA procedure ensured the drilling methodology was constantly adapted to meet project specification.   The homogeneity of the soil and grout were consistently monitored with rotational speed, mixing phases alternated to ensure optimal mixing.     

For validation, Keller planned in situ CPT testing correlated using EuroSoilStab figures of qc/N with N taken as 13.  Using this correlation, undrained shear strengths of 300kPa to 500kPa were achieved.  Considering a target of 100kPa, this corresponds to a FoS ranging between 3.0 and 5.0. 


  • 585 No. 2m deep Wet SM Columns installed at1.5m diameter at 1.3 and 1.35m spacing achieving 150 to 200mm interlock;
  • 390 No. 7m deep Wet SM Columns installed at 1500mm diatmer at 1.2m spacing achieving 300mm interlock in triangular grid pattern; and,
  • In situ CPT testing to determine strength criteria of mass stabilised block.


Client: Down County Council

Contractor: Felix O‘Hare & Co. Ltd

Engineer:  Byrne Looby and Partners Ltd

Year of execution: 2016



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