The picture shows a track section between km 1.300 and km 1.900 (see horizontal axis). The vertical axes represent both depth in m related to top of sleepers and travel time of the waves in nanoseconds.
In that section the ballast has been renewed to a depth of 0.5 m (pale grey layer). Below, there is fouled ballast (dark grey layer). Ballast settlements can be seen between km 1.460 and 1.570. This is an indication for insufficient bearing capacity of the sandy subgrade (yellow layer). Below the sandy formation there is clay to be found. Between km 1.600 and km 1.900 the clay layer is almost adjacent to the ballast bed. In this section, a well working drainage is important. Otherwise water will remain inside the track, leading to eventual stability problems of the track.
The picture shows crossings at km 1.370 and km 1.870. Drillings have been carried out at km 1.550 and km 1.740. In both cases ground water has been found in a depth of 1.2 m.