Ballasted Railway Level Crossing Ground Improvement

Ballasted Railway Level Crossing Ground Improvement

Project Overview

Location and Background

The project focuses on a ballasted railway level crossing located on the South West Mainline. The crossing is part of a high-speed rail line with a line speed of 100 miles per hour and accommodates approximately ten EMGTP (Equivalent Million Gross Tons per annum) of traffic. The level crossing had been experiencing significant deterioration, primarily due to poor track geometry performance. An investigation revealed that the rapid deterioration was caused by a combination of soft underlying conditions and subgrade erosion.

Client challenges

The primary issue was the rapid degradation of track geometry at the level crossing, which posed safety and operational risks. The asset owner required a solution to stabilise the crossing until a replacement was installed during the next five years. 

As the mainline was a busy operational route the client had a significant challenge to retain traffic operations whilst improving the strength of the ground. They required a solution that could be implemented under Rules of Route and within isolated possessions.

Video Case study

Proposed Solution

To address the deterioration, our team proposed a geopolymer injection solution aimed at stabilising and increasing the stiffness of the railway formation. This method involved injecting a specialist geopolymer at specific locations and depths to strengthen the underlying structure.

Design and Implementation

Injection Design

The design involved:

• Injecting geopolymer in pairs at every sleeper bay.
• Targeting a depth of approximately 1.3 meters below ground level.
• Extending the treatment area two meters on each side of the crossing to manage transition issues.
• Ensuring the current track geometry level was maintained to avoid significant variations.

Execution

The injection works were completed within a week during a possession period. The process included the following steps:

1. Installation of injection tubes along the track.
2. Execution of pre-injection dynamic probing to establish baseline formation stiffness.
3. Geopolymer injection according to the design specifications.
4. Post-injection dynamic probing to measure the improvement in formation stiffness.

Results and Analysis

Dynamic Probing and Stiffness Measurements

Graph 1

The dynamic probing results were converted into formation stiffness (formation modulus) measurements. The key findings from the pre and post-injection probing indicated a substantial improvement in the formation stiffness at both ends of the level crossing.

Graphical Evidence

The two graphs illustrate the dynamic probing results:

1. Graph 1: Dynamic probing results at one end of the level crossing, showing significant improvement in formation stiffness post-injection.
2. Graph 2: Dynamic probing results at the other end, also demonstrate a substantial increase in formation stiffness after the injection process.

Client benefits

Graph 2

The fast nature of Geobear solutions meant the track bed could be strengthened under a single weekend possession, allowing for the route to be operated as normal the following Monday. This minimised route delays and, critically, ensured weekday traffic remained operational. 

Furthermore, the solution ensured the formation stiffness was sufficiently increased to minimise any future movement until the full replacement was organised. 

Conclusion

The geopolymer injection method successfully stabilised the level crossing near Stoke Canon. The substantial improvement in formation stiffness met the project requirements and provided a temporary yet effective solution to the rapid deterioration issue.