2. Using recycled ballast in work method for roadbed improvement

A roadbed improvement method was developed using grout injected discarded ballast.
This work method reduces the impact on the environment and is more time and cost effective.

In order to improve soft clay roadbeds associated with mud pumping, it is possible to replace the ballast on the track, however, this traditionally meant that discarded ballast had to be removed and then disposed of. As such, a road bed repair and improvement method has been developed which reuses discarded ballast, reducing the impact on the environment and cutting the cost of the operation (Fig.1). This method not only avoids the need to remove the ballast itself, but also does not require compaction, saving considerable work time.

The developed road bed improvement method is comprised of a two-component rapid hardening grout which is injected to form a supporting layer to improve the road bed. No special equipment or technology is required for injecting the grout, so the method devised is user-friendly (Fig.2).

According to this method, discarded ballast can even be reused on sections of deteriorated ballast which require a complete ballast replacement.

The results of repeated loading tests on a full scale road bed model demonstrated that this method significantly reduces track settlement (Fig.3). In-situ tests further demonstrated the practical applicability of this method and revealed that after improvement work, the need for track maintenance was also significantly reduced. This research was funded by the Ministry for Land, Infrastructure, Transport and Tourism.

Fig.1 Outline of the roadbed improvement method using discarded ballast
Fig.2 Roadbed improvement work
Fig.3 Verification of results from repeated loading tests