Railway Cutting Slope Stabilisation in Surrey

Significant cracks of up to 1m deep appeared in a cutting slope above a section of railway between Brookwood and Woking in Surrey, UK.

Cracks Appeared in the Cutting Slope (Picture from GE Magazine)

Network Rail’s geotechnical and structural operators discovered cracks of up to 45m long, 50cm wide, and 1m deep in some places.

It is expected that repair works will consist of installing 170 steel sheet piles that measure 10m long at the base of the slope – this will make up a retaining wall that should prevent any earth slipping onto the tracks.

The installation of a steel sheet pile retaining wall at the base of a cutting slope involves a systematic geotechnical process.

Before the installation process begins, a thorough site assessment is conducted. Geotechnical engineers analyse the soil properties, slope angle, and other relevant factors to determine the appropriate design parameters for the steel sheet pile wall to raise the factor of safety against slip failure to an appropriate value. The wall design considers the lateral earth pressures, groundwater conditions, and the required structural capacity.

Based on the site-specific requirements, engineers select the appropriate type, size, and configuration of steel sheet piles. These piles are often interlocking and may have various shapes and profiles, such as U-shaped or Z-shaped, to enhance stability and ease of installation.

170 Sheet Piles Will Make Up the Retaining Wall (Picture from GE Magazine)

The steel sheet piles are then driven into the ground to sufficient depth below potential slip planes to gain sufficient resistance from the ground at the toe of the slope. The interlocking nature of the piles helps create a continuous barrier that resists lateral earth pressures and local failures.

To enhance the stability of the retaining wall, anchors or braces may be employed. Anchors are often drilled into the ground behind the wall and beyond potential slip planes and then connected to the sheet piles, providing additional support.

Once the sheet piles are securely in place, the area behind the wall may be backfilled with suitable material to a certain, designed profile. The graded surface ensures proper drainage and minimizes the risk of water-induced slope instability.

Railway Cutting Slope Stabilisation is Crucial for Infrastructure Safety (Picture from GE Magazine)

Continuous monitoring of the retaining wall is essential to detect any signs of movement or instability. This can be conducted through satellite remote sensing methodologies such as InSAR which can track ground movements and deformation around the retaining wall with millimetric accuracy. This should show whether the slope movements have been arrested.