In triaxial tests, a cylindrical specimen, sheathed by a latex membrane, is placed in a water-filled compression cell. There, it is put under stress in radial (σ2/3) and axial (σ1) direction. First, the specimen is consolidated and then sheared off afterwards. Depending on the type of test, the consolidation might be isotropic (σ1 = σ2/3) or anisotropic (σ1 ≠ σ2/3) and during the shearing process the valve controlling the drainage of specimen is either open or closed. A distinction is made between unconsolidated, undrained tests (UU) in accordance with DIN EN 17892-8 and consolidated, undrained (CU) as well as consolidated, drained (CD) tests in accordance with DIN EN ISO 17892-9. The test is a sophisticated variant of a shear test, whereby, in addition to the shear parameters, statements are made about the stress-deformation behavior under almost homogeneous distribution of stress and deformation.
Application and Potential
By measuring and controlling the vertical deformation (ε1) and strain (σ1), cell pressure (σ2 = σ3), the saturation pressure, and the pore pressure, this complex test allows the determination of the strength and deformation properties and the shear parameters of soils under virtually arbitrary stress conditions. From the acquired stress-strain curves and stress paths, the effective cohesion c' and the effective friction angle φ', respectively the undrained cohesion cu, can be derived, as well as important parameters needed for various material models. In addition, special tests can be carried out to estimate the soils tendency to liquefy or its dynamic shear modulus under a dynamic load.
Tests can be performed on undisturbed, recompacted or processed soil samples. They can be saturated or partially saturated. According to DIN EN ISO 17892-8 and -9, cylindrical specimens should have a minimum diameter of 34 mm and an h/d-ratio of 1.8...2.5. The maximum grain size is limited to 1/6 of the specimen diameter.
To determine the effective shear parameters, 3 separate test should be carried out. To make high-quality conclusions, information on the expected stress, drainage and anisotropy conditions, the in-situ density and possibly the overconsolidation ratio (OCR) should be available.
We have hydraulic load frames for loads up to 50 kN with the possibility of load-, displacement- and speed-controlled testing. There is also the option for generating dynamic loads. Using our pressure generators, we can achieve radial compression forces of 1000 kPa. Highly dynamic generation of radial stress is possible. Cells for testing soil samples with a diameter of 38 - 100 mm are available.
- DIN EN ISO 17892-10 (2019): Direkte Scherversuche
- Schwiteilo, Erik; Herle, Ivo (2018): Bewertung von Scherversuchen aus Vergleichsuntersuchungen an feinkörnigem Boden. Aktuelle Themen der Geotechnik (Ohde-Kolloquium 2018). Technische Universität Dresden
- Kolymbas, Dimitrios (2019): Geotechnik. Bodenmechanik, Grundbau und Tunnelbau. 5th ed. Chapter 7.7