Settlement characteristics of unprotected embankment along the Qinghai–Tibet Railway

This study attempts to investigate the settlement characteristics of the unprotected embankment along the Qinghai–Tibet Railway. First, the investigation shows the observed data regarding the settlement of five adjacent unprotected embankment sections. Then, this data is estimated by using the fractal dimension to estimate the roughness of the embankment shoulder surface. Finally, a relationship between this roughness and the differential settlement between adjacent embankment sections is proposed. The result shows that currently the roughness along the north and south shoulder surfaces are 6.25e-8 and 8.92e-8, respectively. These values mean that the differential settlements between 20 m-distance sections along the north and south shoulder surfaces are 3 and 4.3 cm, respectively. Therefore, although the unprotected embankment has experienced significant settlement (maximum is 21 cm), the differential settlement between the 20 m-distance adjacent sections is still of lower magnitude. A prediction for the evolution of the differential settlement of the unprotected embankment shows that by 2020 the differential settlement along the north and south shoulder surfaces of the embankment may reach approximately 4.5 and 9.8 cm. The difference between these two values is 5.3 cm which would change the curvature of the tracks, and thus potentially risk the safety of the running trains.