CASE STUDY

Date: May 2017
Contractor: Kier Living
Project: Harrowby Road, Bilston, West Midlands

Deep Soil Mixing at Harrowby Road
Deep Soil Mixing Harrowby Road

A recent project Deep Soil Mixing Ltd (DSM) undertook for Kier Living and Patrick Parsons Ltd at Harrowby Road, Bilston in the West Midlands has won the Environmental and Sustainability Award at the Institute of Highways Engineers Mercia Branch Awards.

The award was presented to multi-disciplinary consulting engineers Patrick Parsons Ltd for the deep soil mixing works below the adoptable highway at Harrowby Road, Bilston for Kier Living.

The site was being redeveloped by Kier to provide residential properties. The landfilled made ground below a section of road was of such poor quality that CBR values were almost none existent. The local Highways Authority and Severn Trent would not adopt the roads or sewers due to concerns over long settlement and required a significant guaranteed improvement of ground conditions before construction could begin. Initial proposals were for the poor-quality hazardous landfilled material to be excavated, sent to tip and replaced with imported granular fill.

Patrick Parsons Ltd and Deep Soil Mixing Ltd provided a suitable ground improvement method using DSM’s double rotational mixing head to soil mix the ground as well as improving the waste classification of excess materials post treatment.

Installing secant soil mixed columns with a soil mixed slab over, Deep Soil Mixing Ltd used an RTG 19 rig with a double rotary mixing head. This head has cutting teeth at the bottom and mixing bars in the centre that mix the ground with the designed binder that is being pumped into the head while the depth is achieved. The binder is continuously pumped while the shaft is on the way down and on the way back up. The rig calculates the depth of the mixing head so that any required depth can be accurately achieved.

By mechanically mixing the existing soil with a cementitious binder, soil mixing changes the characteristics of weak soil to achieve a geotechnically modified material for numerous applications. This enables more efficient and effective installation and greater ground stability.

The soil that was mixed on site before treatment, contained glass bottles, foundry waste and a general mixture of buried materials.  The soil was quite dry but this proved no problem to the Deep Soil Mixing team and their soil mixing solution and Kier could commence drainage works on site approx. 6 weeks after completion of Deep Soil Mixing Ltd undertaking the soil mixing works.

The adoption of soil mixing to stabilise the fill material provided a significantly more sustainable solution than the previously proposed dig and dump method.  Soil mixing reduces the carbon footprint, as no ground improvement material was imported and more importantly none left the site. and it also had the added advantage of being quicker and more cost effective.

Director Colin Critchlow comments: “We are very proud that the Harrowby Road project has won the IHE Mercia Award for environmental and sustainability project of the year.  That is the ethos of what Deep Soil Mixing Ltd and the solutions we offer is all about, environmentally friendly and sustainable solutions.

Our company and the soil stabilisation solution we provide was selected by Kier Living and Patrick Parsons Ltd because of the specialist but cost effective techniques we use together with the speed of contract completions and importantly our green credentials – Deep soil mixing is a cost effective, environmentally friendly, in situ ground improvement technique that enhances the characteristics of weak soils by mechanically mixing them with a cementitious binder and there is no need to remove material from site.”

ADVANTAGES OF SOIL MIXING

  • No need to excavate existing material on site
  • Minimum spoil removal
  • Wider range of soils can be treated compared to other ground remediation solutions
  • Existing soil is used as construction material
  • No need to bring costly and bulky materials on site
  • Environmentally friendly – Reduction of Carbon Footprint
  • Cutting edge innovative technology
  • With government pressure calling for a reduction in construction excavation waste being sent to landfill. Soil Mixing can help to meet these targets.