ABSTRACT:

The behavior of rock culverts under railroads has been studied using numerical and analytical modeling, complemented by laboratory testing and field measurements. Modeling results suggested a plausible explanation for the separation of rock blocks, and the deteriorated function of the culverts. Agreement between calculated and measured displacements was fairly good. Numerical modeling showed that block separation could be prevented by installing pre-tensioned tendons in the culvert. However, the deformations caused by passing trains only account for part of the total deformation. Other factors, such as frost action, significantly affect the separation magnitude, and need to be studied further. These results have direct application to the currently ongoing upgrade of the railway system in Sweden, to allow larger train loads.

BACKGROUND

During the construction of the railway system in Sweden in the late 19 th and early 20 th century, rock culverts were built to lead streams and rivers under the railway embankment (Fig. 1). These were constructed using large rock blocks, and have had a relatively long life. However, during recent years, extensive damage has been observed in many of these, in the form of separation between the rock blocks making up the culvert and subsidence of the overlying embankment, see Figure 2.

Figure 2. Damage of rock culverts. (available in full paper)

Today, there exist a large number of rock culverts (on average, one every 500 meter along all railroads). The maintenance and the associated high repair costs is expected to increase in the coming years. This coupled with higher demands on allowable train loads (for freight trains) prompted this investigation. The objective of the study was to (1) identify the mechanisms behind damage of existing rock culverts, (2) study the effect of changes in train load on the function of the culverts, and (3) analyze the effects of different reinforcement techniques for repair of rock culverts.

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