Researchers at the Indian Institute of Technology Mandi, and Durham University in the United Kingdom, have developed suction monitoring setup for soil cyclic triaxial testing to investigate the impact of climate change on railway embankments. The findings of this study which was conducted by IIT Mandi professor Dr Ashutosh Kumar along with his colleagues were published in the ASCE Journal of Geotechnical and Geo-environmental Engineering, by the American Society of Civil Engineers.
The main component of railway infrastructure is the track-bed, which is supported by earthworks. This is mainly used to support the track infrastructure and carry the load imparted by the moving traffic. The present design protocols only consider the load developed due to the moving train thereby ignoring the real case scenario of changing the natural state of the soil due to ingress and egress of water.
Often, soil used in earthworks is compacted and remains unsaturated during its lifetime. Seasonal variations in terms of precipitation and drought are capable of altering the amount of water present within this compacted soil mass which can alter the strength of the embankment. This is a result of climate change which causes intense rainfall. "Compacted soil is susceptible to deteriorate under the changing climatic conditions due to changes in the water holding capacity of the soil. And this causes loss in the soil strength. Therefore, this study developed a setup to monitor changes in soil suction and deformation brought 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 that connects around 40 mines to the Richards Bay Coal Terminal in South Africa.
The research work that went into the project would now allow understanding of the coupled impact of traffic-induced loading and environmental loading on the long-term performance of unsaturated soil present within the railway embankments. The setup uses a high-capacity tensiometer developed at Durham University to measure suction.
“We have adopted three testing protocols. First, under the condition of train loading, we allowed the water from the soil to drain freely when the soil voids were filled completely with water as a result of intense rainfall. We then conducted a test under constant water conditions replicating constant weather conditions under the given traffic conditions. We followed this by replicating the condition of the train loading under the ongoing event of rainfall. This information was used to identify the potential deterioration of soil strength due to wetting and drying cycles. The deformation in the soil was associated with water infiltration leading to a reduction in suction and hydraulic history," explained the scientists.
The results obtained indicate that 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 field conditions. This would help to develop strategies to mitigate climate risk at the design stage of railway embankments, leading to more sustainable construction.