The simple shear device at UBC is a modified NGI type. A cylindrical soil specimen is laterally confined by a steel reinforced rubber membrane. The reinforced membrane enforces an essentially constant cross sectional area, therefore if vertical displacement is prevented, constant volume conditions are simulated.
The simple shear apparatus applies plane strain loading in one direction, and enforces zero extension in the other perpendicular horizontal direction. It also imposes uncontrolled rotation of principle stress during loading while the sample is being sheared under plane strain. The ability to simulate principle stress rotation is common to many geotechnical problems, including earthquake loading.
The device has extensively been used to study the static and cyclic stress-strain response of sands and silts.
Diameter = 6.9 cm , Height = 2 cm
Vertical stress is applied by a single acting air piston controlled by a regulator. Horizontal shear stress (monotonic or cyclic) can be applied by either a double acting pneumatic piston for stress controlled loading or by the variable speed motor for strain controlled loading.
Cyclic loading is applied by changing the pressure in one of the two chambers of the double acting pistons, using a computer-controlled electro-pneunatic transducer.
- Data acquisition using "National Instruments USB 6341 X Series data acquisition unit"
- 4 Analog to Digital input channels: 4 A/D channels for transducers: Load cell (2), LVDT (2)
- 2 Digital to Analog output channels: One D/A channel controls the Electro-Pneumatic Pressure Regulator
- One D/A channel amplifies LVDT (horizontal) signal
- DAQ is capable of gathering 6000 data sets per second.
- Gathered data is averaged over 100 readings to reduce electrical noise.
Signal conditioning is done before feeding the signals into data acquisition unit.
|Load Cell||Vertical Stress||0.15 kPa|
|Load Cell||Sheer Stress||0.05 kPa|
|LVDT (Horizontal)||Shear Strain||0.0031%|
|Electro-Pneumatic Pressure Regulator||Apply and Control Shear Stress||0.1 kPa|