The Thrandeston Bog embankment, on the Great Eastern route from London to Norwich, is 16 feet (5 meters) high and 2,133 feet (650 meters) long.
The embankment suffered from continual settlement and was in danger of failure. Thrandeston Bog consists of 33 feet (10 meters) of peat and very soft clays over chalk.
For the client Network Rail, we carried out research and trials to demonstrate the viability of dry soil mixing, a technique previously untried on British railways. Dry soil mixing uses an augur to whisk cement powder into the ground, creating columns of stiff material.
The reference design for the project consisted of 1,200 tubular steel piles measuring 36 inches (914 mm) in diameter and with a combined length of 11 miles (18 kilometers), forming continuous retaining structures on either side of the embankment.
The cost of cement for the matrix of 11,500 soil mix columns was less than 50% the cost of steel piles. 5500 metric tons of cement powder were used instead of 7,300 metric tons of steel. Embodied carbon dioxide emissions totaled 5,400 metric tons instead of 17,600. Fewer vehicle movements were also required.
One benefit of the technique was that plant that could be used adjacent to the live railway and within 9 feet (2.75 meters) of the overhead lines.