Numerical simulation of efficient cooling by coupled RR and TCPT on railway embankments in permafrost regions

•A 3-D coupled model (comprising RR, TPCT, and soil) is established and verified.•Cooling efficiency of CRRT for the sunny shoulder of embankment is analyzed.•Efficiency of the single part in the coupled system is analyzed.•Environmental effect of CRRT is analyzed.•Conclusions and suggestions are proposed for a better design of CRRT.