Simple Shear
Initially designed by NGI and manufactured by Geonor, the direct simple shear (DSS) apparatus has been modified in house, to allow stress- or strain-controlled shearing and controlled vertical loading. An electric screw jack actuator has been added to control vertical loading, combined with a 4 kN capacity load cell. Another electric screw jack actuator was added to apply horizontal shearing to the specimen, while linear variable differential transformers (LVDTs) record both vertical and horizontal displacements. A new control system has been implemented, allowing control of stress and strain loading.
The modified DSS apparatus allows uniform shearing of a soil specimen throughout its volume. The top plate translates horizontally relative to the fixed base. Cylindrical soil samples of 55, 65, or 79 mm diameter and 25 mm height can be tested. The specimen is confined either in a wire-reinforced rubber membrane or in an in-house developed laminar container, not allowing the development of radial strain during the test, forcing the horizontal cross-sectional area of the specimen to remain constant. The apparatus allows different types of tests to be conducted, including direct simple shear (DSS), to measure the degradation of shear modulus (G) and the increase of damping ratio (ξ) with shear strain and initial vertical effective stress, as well as constant volume direct simple shear tests (CVDSS), to determine the cyclic stress resistance of liquefiable sand.
The technical specifications of the simple shear test apparatus are summarized as follows:
- Specimen diameter: 55 mm, 65 mm and 79 mm
- Maximum horizontal displacement: ± 2 mm
- Frequency range: up to 1 Hz
