A new Swedish dry soil mixing technique has been used for the first time in the UK to construct a sea bund in Hull. A number of previous attempts by main contractor Birse had been thwarted by the extremely soft marine clays on which the bund had to be constructed, which led to it failing through ground shear. Birse called in Keller Ground Engineering, which used the technique to strengthen the clays so that they could take the load of the bund.
At the heart of the system is a two-bladed auger which is screwed into the ground to a predetermined depth. As it begins to withdraw, a dry blend of Portland cement, pulverised fuel ash and an admixture is blown into the soil at high pressure through a nozzle mounted just above the blades.
Blowing continues as the auger withdraws, mixing the dry blend into the soil to form insitu columns of stabilised material. On the Hull project, the columns were a nominal 900mm diameter at 1500mm centres and up to 8m deep, formed down to the underlying competent strata.
A geogrid reinforced granular mat was then placed over the columns to distribute loads among them before the bund was gradually extended over the top.
All work was carried out between tides, and a second phase of construction will start in April.
INFOPLUS www. keller. co. uk