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The background

Geotech Soil Stabilisation Ltd (Trading as Geobind) carried out initial testing as per the requirements of the relevant British, European and Earthworks standards on the ground strata at Darlington.

Testing of different binders (GEOBIND®, Cement, Quick Lime) was carried out at Optimum Moisture Content, which is suggested best practice when carrying out traditional Lime and Cement stabilisation.

The testing revealed that the ground strata was very expansive in nature, which resulted in high volumes of swelling. All stabilised specimens experienced high volumes of swell.


The risk

The potential for ground swell caused serious concerns. If the ground strata were to swell and expand underneath the new distribution centre, it would decrease the load bearing and stiffness capabilities of the ground which is required to support the structures above. This could lead to the following:

  • Subsidence of the distribution centre and associated structures
  • Cracking of concrete floor slabs
  • Cracking/Rupture of asphalt surfaces from ground swell.

The above factors were considered a massive health and safety risk and financial risk.


Problem Identification

Geotech Soil Stabilisation Ltd quickly put together a number of theories as to what could be causing the excessive swelling. The most likely theory was that there were high sulphates/sulphides present in the ground strata, however this was quickly ruled out. Geotech Soil Stabilisation Ltd implemented Rapid On-Site Analysis Testing which quickly showed that the levels of sulphates/sulphides at the site should not be detrimental and cause excessive swelling. This was later backed up by UKAS laboratory test data taken on the same samples.

It was then theorised that the cohesive subsoil at the site in Darlington, when coming into contact with water, would try to re-hydrate itself. To test this theory different subsoil samples were taken from the site and mixed with GEOBIND®, Cement and Quick Lime at different moisture contents. It was found that material stabilised below the natural moisture content occurring at the site would take on additional water and swell.


The Solution

Geotech Soil Stabilisation Ltd then commissioned further testing using GEOBIND®, Quick Lime and Cement mixed with the subsoil/clay at Natural Moisture Content. The results showed that the samples stabilised with GEOBIND® at Natural Moisture Content did not experience a swell issue, whereas the samples stabilised with Cement and Quick Lime did experience a swell issue.

In addition to carrying out the stabilisation process at Natural Moisture Content, the GEOBIND® addition rate was increased. The reason for this was that it provided an increased amount of stabilisation reactions to occur, which filled the pore space in the cohesive subsoil. By filling the pore space in the cohesive subsoil, this prevented the pore spaces filling and expanding in the presence of water. This can be demonstrated by the swell and CBR test results achieved on stabilising the blue clay material with GEOBIND® at Natural Moisture Content. The GEOBIND® Stabilised Blue Clay monolith, after being submerged for 28 days, only experienced a swell of 0.7mm and also achieved a CBR stiffness of 40.14%

Testing was also undertaken to establish whether the swell issue with the cohesive subsoil was just isolated to the Darlington Site or whether it was a problem with cohesive subsoil in the Darlington area. Cohesive subsoil was taken from 3 different Recycling Facilities within a 20 mile radius, mixed with GEOBIND® and tested for Swell and CBR at 28 days. The results proved very positive and pointed to the fact that the swell issue was just isolated to the Darlington site.


The result

  • Over £2,000,000.00 Cost Saving
  • Strengths far exceeded requirement
  • Programme reduced by 15 weeks with further cost savings in prelimenary cost
  • Primary aggregate reduced from 151,268 tonnes to 33,278 tonnes
  • Vehicle movements reduced from 16,808 to 1,849
  • Associated carbon emissions reduced from 72,383 tonnes to 3,060 tonnes
  • Multiple designs for different end uses, standard compound treatment, reduced thickness piling mat design and IAN73/06 compliant adoptable highways design
  • Combined earthwork and stabilisation excercise
  • 89% reduction in wagon movements 89% 89%
  • 95% reduction in associated carbon emissions 95% 95%
  • 79% reduction of primary quarried aggregate 79% 79%
  • 100% reduction in export disposal 100% 100%

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