Identifying Roadbed Instability
a. Initial evidence of roadbed instability is a continual loss of line and surface despite satisfactory rail and tie
condition and an assumed adequate ballast section. Loss of line and surface may continue even after several
ballast applications followed by lining and surfacing operations. A muddy, fouled ballast section and heaved
track shoulder (see Figure 1-1-13) are other indications of roadbed instability. Excess moisture and poor
drainage conditions are so closely related that evidence of either can almost be considered as an indicator of
roadbed instability. However, caution should be used before identifying a muddy fouled ballast section as
roadbed instability. In some cases internal abrasion and weathering of the ballast or windblown dirt and car
droppings will cause a fouled ballast section and give the appearance of roadbed instability. If any doubt
exists as to the cause or extent of roadbed instability; subsurface explorations, sampling and geotechnical
testing of the roadbed materials should be performed. The technique of excavating a trench several feet
deep across the width of the ballast section for the purpose of exposing the layers, thicknesses, and relative
positions of the roadbed materials is strongly recommended as an aid in the planning any roadbed corrective
measures. See example in Figure 1-1-12.
b. Vertical and lateral displacements of the roadbed as evidenced by loss of track line and surface may actually
originate beneath the roadbed zone. The possibility that embankment, slope, or foundation stability
problems exist and are contributing to roadbed displacements should be investigated and analyzed before
attempting roadbed corrective measures. Refer to Article 1.2.2 and Article 1.2.3 for further information.