Deformation behaviour of railway embankment ... - Liikennevirasto

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Figure 8.7.2:2 Schematic illustration of the repeated load triaxial apparatus (Lekarp
1999).
The axial load is applied to the specimen through the loading platens and is
continuously monitored by a load cell. The feedback signal from the load cell is
compared with the load command signal by the digital control system, after which an
error signal is relayed to the servo-valve on the actuator so as to correct the load applied
to that required. The confining stress is controlled in a similar manner by the output
signal of a pressure sensor placed inside the triaxial cell. For the application of
confining stress, silicone oil is used as the confining medium. The compacted specimen,
sealed between the top and bottom loading platens by rubber membranes, is
instrumented with LVDTs for the measurement of axial and lateral strains. The output
signals from the load cell, the pressure transducer, and the LVDTs pass through the
conditioning unit and are finally registered at chosen intervals in a data file in the
computer. The entire testing process is run with the aid of computer software.
Loading frame
The purpose-made loading frame (Figure 8.7.2:1) consists of two joint frames and
enables the application of both the deviator stress and confining pressure. The main
frame has a capacity of applying a repeated load of 250 kN and is used to generate the
axial load. A second frame is welded to the right-hand column of the main frame and is
designed for a maximum repeated load of 50 kN required for applying the confining
stress. During testing, the triaxial cell rests on a 500 x 500 x 20 mm steel seat welded to
the lower beam of the main frame. This seat restricts the movement of the triaxial cell
during testing and ensures that the applied load is effectively transmitted to the body of
the loading frame.