Modern railway infrastructure demands a high level of performance in terms of settlements and stability of the railway track. In areas where loose or soft cohesive deposits are found, ground improvement is often required to ensure the required level of performance.
This paper presents some of the ground improvement techniques that are available from Keller Group companies and being used worldwide for railway infrastructure projects. The techniques presented are Vibro Compaction, Vibro Replacement (Stone Columns), Grouted Stone Columns (GSC), Vibro Concrete Columns (VCC) and Deep Soil Mixing (Cement Columns).
The purpose of this paper is to provide a general introduction of the techniques to Owners, Designers and Project Managers and to illustrate their application by describing case histories from Europe, USA and Malaysia.
Railways are one of the oldest mode of transportation systems started some 150 years ago under different traffic conditions as far as speed, axle loads and traffic intensity are concerned. Increasingly, there are greater demands from modern railway organisations to increase the axle loads and train speeds both for economic and environmental reasons. In addition to increased axle loads and train speeds, railway lines often have to cross over existing loose or soft cohesive deposits as a part of the alignment giving rise to the need for ground improvement.
In order to achieve a high level of performance of the rail system, attention should be focused on post construction settlements of the subsoil and factor of safety of the structure against slip failure. Different countries follow different sets of specifications for settlement and stability criteria for railway systems. For example in Malaysia for a railway line designed for speeds of 160 km/h, typical requirements are as specified below:
- Maximum post construction settlement of 25mm over a period of 6 months of commercial rail service.
- Maximum differential settlement of 10mm over a track length of 10m (1 in 1000) along the embankment centreline.
- Minimum long-term factor of safety of 1.5 against slip failure.
Apart from the settlement and stability criteria, another important criterion is to mitigate vibrations induced by high-speed trains in order to achieve acceptable dynamic performance of the rail system. By improving the subsoil characteristics, it is possible to mitigate the vibrations to the surrounding structures.
Author: V. R. Raju