ISMGEO Large Triaxial Apparatus

The design of earth and rockfill dams is focused on ensuring the stability of the structure under a set of combined mechanical and hydraulic conditions that may occur both during construction and operative life of the dam. The prediction of the hydro-mechanical behavior of construction materials (which range from clayey soils to rockfill) is therefore fundamental. The most important characteristics to be studied are static and dynamic shear strength, shear stiffness at small and intermediate strain and compressibility of the construction materials. Testing of these properties is typically performed using the triaxial apparatus. However, testing large size materials such as rockfill requires the use of large triaxial specimens, whose diameter depends on the particles maximum dimension. Facilities capable of testing large grain size materials are few and sometimes neither the largest apparatuses are big enough to test particles as large as cobbles and boulders. ISMGEO large triaxial apparatus allows the execution of static and cyclic test on 300 mm diameter samples. The maximum particle dimension is 50 mm. Originally designed for testing the gravelly foundation soils of the Messina strait bridge, the apparatus has been recently up-graded in order reach a cell pressure of 2.5 MPa, thus allowing to reproduce the in situ stress conditions within particularly tall earth and rockfill dams. This paper describes the main features of the facility. Application examples are also shown. In particular, results of motononic compression test and cyclic tests are analyzed, with the main aim of evidencing the apparatus capabilities.