Mowlem Piling & Foundations, working for Mowlem Remediation, has just completed what is thought to be the largest soil mixing contract of its type on a former municipal landfill site in Northampton.
The project involved installation of two barriers to stop contaminated groundwater getting into nearby watercourses.
Both barriers were formed by mixing grout into the ground to depths of approximately 7m.
The first is a cut-off wall that acts as a 'passive' barrier, channelling the groundwater to a second, 'active' barrier. This wall is formed in the same way, but the grout contains chemicals that remove the contaminants before the groundwater passes through.
Mowlem used two piling rigs to carry out the work, with the grout mixed at a purpose-designed batching plant on site capable of supplying 140m 3 of concrete a day. The soil mix columns were installed in a 'hit and miss' pattern - with alternate columns installed on one day and then the gaps fi lled the next - at a rate of approximately 40 a day. The work was completed in less than six months, despite numerous interruptions to deal with the 180 obstacles found on the site - which included large concrete foundations.
Total barrier length is 1.5km, made up of 3,500 columns.
www. mowlempiling. co. uk