Researchers strive to understand the impact of climate change on railway embankments

Researchers from Indian Institute of Technology Mandi and Durham University in the UK have developed a suction monitoring setup for cyclic soil testing to study the impact of climate change on railway embankments.

The results of this study have been published in the ASCE Journal of Geotechnical and Geoenvironmental Engineering, USA. The journal is published by the American Society of Civil Engineers. According to the team, the main component of railway infrastructure is the roadbed which is supported by earthworks and is mainly used to support the track infrastructure and carry the load transmitted by moving traffic. “Current design protocols only consider the load developed due to the moving train, thus ignoring the real scenario of changing the natural state of the ground due to water ingress and egress. “Often the soil used in earthworks is compacted and remains unsaturated for its lifetime. Seasonal variations in rainfall and drought are capable of altering the amount of water present in this compacted soil mass, which can alter the strength of the embankment,” said Ashutosh Kumar, assistant professor at the School of engineering from IIT Mandi.

We all now understand the reality of climate change which causes intense rainfall and compacted soil is susceptible to deterioration under the changing climatic conditions due to changes in the water holding capacity of the soil causing hysteretic loss of soil strength. ground, he said. “Furthermore, repeated loading of trains can exacerbate the deterioration process which would eventually lead to premature track degradation and resultant failure,” he added.

Kumar further explained that understanding the coupled impact of train and environmental load is key to designing and maintaining the railway embankment against the changing climatic conditions. “Therefore, this study developed a setup within a cyclic triaxial apparatus to monitor changes in soil suction and deformation caused by traffic-induced cyclic loading and environmental loading, which can be used to assess climate risk at the design stage of railway embankments,” he said.

The soil sample used in the study was taken from a 650 km heavy haul South African coal line that connects around 40 mines to the Richards Bay coal terminal in South Africa.

“The research is unique in that it would now provide an understanding of the coupled impact of traffic-induced cyclic loading and environmental loading on the long-term performance of unsaturated soils present in railway embankments. “The setup uses a large capacity tensiometer developed at Durham University to measure suction and on-sample displacement transducers to measure strain in the ground under the coupled load of environment and traffic,” said Kumar.

He said three testing protocols have been adopted. “Firstly, under train loading condition, we allowed ground water to flow freely when the ground voids were completely filled with water as a result of heavy rains. We then performed a test under constant water conditions replicating constant weather conditions under the given traffic conditions,’ Kumar said.

The team followed this by replicating the condition of the train loading under the continuous rain event. This information was used to identify potential deterioration in soil strength due to wetting and drying cycles. Soil deformation was associated with water infiltration resulting in reduced suction and hydraulic history, the researchers said.

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Maria D. Ervin