A review on the cooling effect of duct-ventilated embankments in China

Duct ventilation, or called air duct, has been used to cool the embankment of the Qinghai-Tibet Railway (QTR). In the past decades, the cooling effect of air ducts has been the subject of numerous investigations, including field observations, innovative designs, and numerical simulations. This review summarizes field observations associated with the cooling effect of air ducts by comparing temperature distributions of duct-ventilated roadbeds with those of earthen roadbeds. Innovative duct designs with temperature-controlled shutters, vertical chimneys, self-adjust windward vents, and overlain crushed-rock layers are assessed in terms of their cooling capacity and constructible feasibility. Numerical method to predict the duct-ventilation embankment temperature is reviewed with the focus on the duct-internal boundary specification. Air convection ducts used in Northern America are compared with ducts applied in China. Some in-service ducts in the QTR's embankment have been plagued with cracking and even failures, calling attentions on the long-term stability of the ducts, especially of reinforced concrete ducts.