120 Drains – 32 Stone Columns

The South Dam Stone Column Trial project was completed for Vale – formerly Inco – Nickel Mines in Sudbury, Ontario. Where Inco operates the largest nickel smelting operation in the world and has the second largest freestanding chimney in the world, at 1,250 ft. The project consisted of the installation of a stone column test area, with wick drains at intermediate points between the stone columns. The test area is designed to increase the soils strength behind the South Dam, so that a large buttress can be installed to increase the factor of safety of the dam.

Prior to the start of works, the test area surface soils were excavated between two and three feet, filled with crushed stone and roller compacted to support the heavy soil improvement equipment. The depth of improvement was about 8 m across the test area.

In consideration of the poor existing ground conditions encountered at site, it was required to
carry out this ground improvement test area to establish suitable design criteria for potential
future stone column installation works downstream of the toe of the existing dam, including assessing a practical area replacement ratio, the maximum stone column diameter, effective installation techniques and appropriate grid layout for the stone columns.

The wick drains were installed prior to the stone columns to aid in the dispersion of the excess
pore pressures and air introduced to the soil during installation of the stone columns.