Issue 30

A. De Iorio et alii, Frattura ed Integrità Strutturale, 30 (2014) 478-485; DOI: 10.3221/IGF-ESIS.30.58 481 characterization tests on the components and materials that were not already tested by the suppliers. On the basis of the choices made to define the scenarios, the ballast was the only material/component that needed a special investigative attention; for it both a geometrical characterization test program, to be carried out in the laboratory on the aggregate, and a series of loading and seismic tests in the service conditions (on the instrumented track) have been defined. In particular, the latter tests have been planned in order to evaluate those parameters that can affect the ballast capacity of constraining in the long run the displacements of the sleepers in their axial direction, under the action of the destabilizing forces acting on the rails. E XPERIMENTAL METHODOLOGIES AND TESTING PLAN n the laboratory the following characterization tests, in accordance with the Standard shown in brackets, have been planned for the rocks that compose the ballast:  Granulometric properties of Ballast grains (UNI EN 933-1 4/99);  Shape index (UNI EN 933-4 4/01);  Apparent particle density of ballast grains (UNI EN 1097-6 Ann. B 2/02);  Los Angeles-test (UNI EN 1097-2); In order to characterize in situ the ballast, in other words on the instrumented permanent way, the following tests have been introduced in the plan:  Dynamic plate load test;  Seismic tests. The chosen kind of seismic test is the Seismic Refraction Profile in P and S wave velocities and has an investigation depth of 1 m. It consists in positioning along a line-up (sub horizontal and straight – for instance parallel and external to the track) n. 12 seismic sensors (geophones), 0.5 m far-between them and fixed in the ballast; along this alignment, n. 5 explosion points for the P-wave are positioned, two of which placed outside the furthest geophones (G1 and G12 in Fig. 1) at 0.25 m from them, one placed at the centre of the alignment and two in-between the furthest and the central explosion points. Figure 1 : Arrangement layout of the geophones and the explosion points in the seismic tests. Also, n. 2 explosion points for the S wave outside the furthest geophones (coincident to the first two for the P wave) will be realized by whacking with a hammer the vertical faces of a metallic plate having parallelepiped shape. To understand, then, the influence of other structural parameters of the tracks on the stability of the system, tests on track panels reproducing the planned scenarios have been scheduled. These tests consist in applying on the rails a load I