Fareham Tunnel blockade aids landslip prevention
A nine-day blockade has helped to prevent future landslips on the challenging Fareham-Eastleigh line.
Shoring up the steep sides of a deep cutting near Fareham Tunnel in Hampshire has been an urgent task to prevent future landslips, to which the line between Fareham and Eastleigh is prone.
It was dug into soft clay in 1841, with sides that feature trees and bushes that have not been cut back for decades. Clearly visible are several small slips, perilously close to gardens, garages and sheds.
The route was closed for nine days from June 25-July 4. Services between London Waterloo and Portsmouth Harbour started and terminated at Eastleigh and Fareham, with some Great Western services to Bristol also affected.
“We’ve had a few small landslips at the top of the cuttings in front of Fareham Tunnel. The slopes are in really bad shape. What we’re putting in is basically a wall of steel piles and concrete to prevent the sides slipping down,” said blockade director Jeff Rose.
“If we didn’t do this piece of work, the cutting would wash away with the increase in heavy rain we’ve been seeing. That could close the railway for a long time.
“And it’s not only a railway problem. There are a lot of houses around the top of the cutting. They would start losing their gardens.”
The route has a troubled history of landslips. The biggest was at Botley in 2014 - the largest railway landslip recorded in southern England, it closed the line for six weeks. Contractors had to build a 2km (1.2-mile) temporary road across fields, to bring in more than 2,000 lorry loads of material to replace 30,000 tonnes of washedout waterlogged clay.
After the collapse, contractor Osborne (now renamed Octavius and also doing the Fareham scheme) said it condensed two years of normal work into just a few weeks to get the line open.
This time, trains have been used to bring construction materials in and out, to minimise disruption to a suburban area.
Zen Nichols, senior programme manager for Network Rail, also worked on the Botley landslip eight years ago.
“These slopes were built much steeper than we would do today,” he told RAIL.
“We are making the cutting sides shallower, so they are more resilient to the rainfall and weather events that we are now seeing.
“These are very old cuttings. They are certainly not up to current engineering standards.”
The line was built by navvies using little more than wheelbarrows and shovels, with whatever material was close at hand, and the railway suffered from earthworks problems right from the start.
Fareham Tunnel partially collapsed before it even opened.
A two-mile diversionary route was created around the tunnel, called the Funtley Deviation. It closed in the 1970s and today is a footpath.
There are 600 miles of similar clay structures on the railway in southern England. Each are especially susceptible to the warmer, drier summers and more intense winter rainfall that a changing climate is bringing. In summer the clay dries out, causing large cracks. These fill more quickly during sudden rainfall, reducing the tensile strength of the soil, leading to sudden collapse that can be difficult to predict.
Adapting these Victorian structures will take decades and cost billions of pounds, at a time when money is in short supply. The risk of landslips close to the singletrack Fareham Tunnel propelled this project to the top of Network Rail’s Wessex Region’s to-do list.
The opportunity was also taken to complete more than 40 other tasks along the route.