Mass stabilisation means increasing the strength and dynamic stiffness of the soft soil by adding binding agents such as cement, lime or fly ash. It improves deformation properties of the soil and can also be used to remediate contaminated soil.

Mass stabilisation has its roots in Japan but Finnish geologists have put lots of resources into developing the method since the end of last century, and the only manufacturer of specialised machines for mass stabilisation comes from Finland.

Ideachip’s product development team design ALLU products for mass stabilisation. ALLU products have been developed in close collaboration with customers and, as a result, quick and cost effective working methods have been invented.

Using mass stabilisation to support pipeline trenches

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Finland-based Hyvinkään Tieluiska Oy is a pioneer in mass stabilisation work. Since 2003, the company has been applying mass stabilisation in difficult job sites. One of those was a pipeline project in Sundet, southern Finland, which was in a newly built residential area.

Site Manager Markku Hurskainen says that the land was soft clay in many parts and the clay was too soft to carry an excavator or even to dig the trench. The only reasonable way to make the trench for pipelines and cables was to mass stabilise the land then place the pipes and cables in the trench.

Mass stabilisation requires special machinery

In total 30,000 m3 cubic metres of clay were stabilised. Normal cement was used as a binding agent and it took 100 kg of cement per cubic metre. The cement was fed from the ALLU Pressure Feeder unit through a pipe that is connected to the PowderMix mixing unit, with the PowderMix installed on the excavator.

The stabilisation system is controlled by the ALLU Data Acquisition Control System that records all the data during the stabilisation project and provides the possibility to transfer data onto other computers. It allows the operator to set the quantity and control the flow of the binder accurately.

Hyvinkään Tieluiska is one of the customers involved in the product development of the ALLU stabilisation system. For them an effective and intelligent system plays a key role when doing mass stabilisation work.

Reusing soil in back filling

After the stabilisation the ground needed to harden for four weeks. The final filling of the site was made with light gravel and mud that was gathered from the site.

Director of the Hyvinkään Tieluiska, Valto Tikkanen said: “Reusing the soil that was dug out from the pipeline trench saved lots of money and time and also the environment when the site traffic was reduced to a minimum. There was less need for new materials too. According to our calculations, we were now able to build up to 60 metres of pipeline trench per day. If we would have used any other method the speed would have been only 10 metres per day.

“Thanks to the homogenous stabilisation result there are no depressions on the area where mass stabilisation method was used.” The aim was to create a ground that will flatten steadily by itself.

“The mass stabilisation was a perfect solution because it made possible to install pipelines and cables and at the same time make a two metre wide solid foundation for roads,” said Mr Tikkanen.