Speakers
Description
For many old structures like earthfill dams, there is a lack of information about the geotechnical parameters. Often, it is not documented how the values for friction angle and cohesion have been determined, especially the boundary conditions, e.g. the used test apparatus, the modification of the grading curve etc. Normally, new calculations have to be performed based on newly verified parameters, which means to carry out new laboratory tests. Having maximum grain diameters of up to 400 – 800 mm, it is difficult to get and to define a representative sample. With the use of direct shear boxes of 500 mm x 500 mm, grain diameters up to 63 mm can be tested with a satisfying accuracy.
In this paper selected case studies are presented to describe the procedure used in the TU Wien soil mechanics laboratory to determine the shear parameters for earth static calculations using large-scale shear tests on dam fill materials. It shows how the grain size distributions for the tests were modified (restriction of the maximum grain size) and how the desired density for the tests can be achieved. Furthermore, the boundary conditions for conducting the tests are presented, with particular attention paid to equipment- and test-related factors that can influence the test results and must therefore be taken into account when conducting the tests. These include, for example, the influence of the behavior of the upper shear frame, which can be either “fixed” or “floating and weight-compensated.” Measurements have shown that this can significantly influence the shear parameters.