IIT Mandi researchers develop a setup to study the impact of climate change on railway embankments
Researchers from the Indian Institute of Technology Mandi and Durham University in the UK have developed a suction monitoring setup for cyclic triaxial soil testing to study the impact of climate change on railway embankments. The results of this study, conducted by IIT Mandi Professor Dr. Ashutosh Kumar, along with his colleagues, have been published in the ASCE Journal of Geotechnical and Geo-environmental Engineering, by the American Society of Civil Engineers.
The main element of the railway infrastructure is the track bed, which is supported by earthworks. This is primarily used to support the track infrastructure and support the load imposed 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 terms of precipitation and drought are likely to modify the quantity of water present in this mass of compacted soil, which can alter the resistance of the backfill. This is the result of climate change which causes intense rainfall. “Compacted soil is likely to deteriorate under the changing climatic conditions due to changes in soil water holding capacity. And this leads to loss of soil strength. Therefore, this study developed a setup to monitor changes in soil suction and deformation brought about by traffic-induced cyclic loading and environmental loading, which can be used to assess climate risk at the design stage of railway embankments,” said Dr Kumar. The soil sample used in the study was taken from a 650 km heavy haul South African coal line. which connects some forty mines to the Richards Bay coal terminal in South Africa.
The research carried out within the framework of the project would now provide an understanding of the coupled impact of traffic-induced load and environmental load on the long-term performance of unsaturated soils present in railway embankments. The setup uses a large capacity blood pressure monitor developed at Durham University to measure suction.
“We have adopted three test protocols. Firstly, under the train loading condition, we let the ground water flow freely when the ground voids were completely filled with water from heavy rains. We then ran a test in constant water conditions replicating constant weather conditions under the given traffic conditions. We followed this by reproducing 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 has been associated with water infiltration resulting in reduced suction and hydraulic history,” the scientists explain.
The results obtained indicate that the deformation and reduction in soil strength are due to the combined impact of cyclic and environmental loading. The suction monitoring setup can test the soil sample that has undergone the seasonal variation either in the laboratory environment or under field conditions. This would help develop strategies to mitigate climate risks at the design stage of railway embankments, leading to more sustainable construction.