When labor-saving grouted ballast track is laid on a track bed of cohesive soil, the track bed surface may be softened by repeated train loads, causing outflow of track bed soil or failure of the grouted layer. The Railway Technical Research Institute has proposed a method known as the bentonite liner for track-bed surface (BLITS) as a simple track-bed damage prevention measure for newly laid labor-saving grouted ballast tracks on existing lines. This is a simple method involving the insertion of a bentonite liner (i.e. a sealing layer of bentonite cohesive soil) between the grouted layer and the track bed to prevent softening of the track bed surface and the outflow of track bed soil (Fig. 1). The RTRI compiled a guide for the application of this method and developed an optimal bentonite track-bed stabilizing agent. This agent, which features high visibility under floodlights for nighttime work (Fig. 2), is an environmentally friendly material that meets the soil environment standard set by the Ministry of the Environment. The method, which has already been applied to commercial service lines, is thought to contribute to a reduction in the risk of damage on labor-saving grouted ballast tracks.
The RTRI also developed a hot-blast drying method to dry the surface of the softened track bed before re-grouting (Fig. 3) as an effective measure in the repair of existing labor-saving grouted ballast tracks that have sunk due to track bed damage. By implementing a life-size model test, the RTRI confirmed that this drying method substantially improves the effect of re-grouting carried out to repair damaged track beds (Fig. 4). The RTRI plans to promote the commercialization of this drying method so that it can be quickly implemented within the tight limits imposed by train operation.