Image shows the Shear Machine with a PC, which is not included in the standard specification. Local purchase is recommended.

Design

The 305mm (12") Square Direct Shear was specifically designed for testing large soil sample sizes with soil and geosynthetics for testing coefficient of friction. Several methods of testing can be accomplished - soil to soil, soil to geosynthetic, geosynthetic to geosynthetic and GCL to GCL (geosynthetic clay liner).

The device utilises the "CONBEL” concept for consolidation loading of the sample. Sample loads are obtained by one of two pneumatic pistons. This concept increases the accuracy and sensitivity of light load settings. A small diameter rolling diaphragm piston is capable of applying light loads to 454 kg (1,000 lbs) and larger piston applies loads up to 90kN.

Castors on the machine and compaction table make for easy movement in the lab. The machine height is a factor in the design to give the operator a convenient level for setting up and operating the machine. This includes the Compaction table that makes the sample easy to prepare in the shear rings. The rings are easily handled both installing and removing from the water chamber and the compaction table.

Software

is provided with the machine to input test data to a computer (not provided) and export to Microsoft "Excel” for graphing and presenting test results.

Controls

Applying the vertical load is accomplished by setting the precision regulator to the required pressure per the pressure to load calibration chart. Load settings are verified on a pressure readout that reads to two decimal places and is accurate to 0.25%. Constant rate of displacement for the horizontal shear rate is set using the digital thumb wheels on the control panel. Limit switches are used for the home position and also to limit the travel to 102 mm (4.0"). Adjustment to the limit switches can be accomplished under the control cabinet.

Measurement

Consolidation and shear displacement are measured by linear displacement transducers and displayed on the digital readout along with shear load from the load cell attached to the water chamber. Data output to the computer is via an RS232 Serial Port in ASCII format. This can be exported to spreadsheet programs like "Excel”. Viewing of displays are not dependent on a computer hookup. Readout is capable of showing peak shear load.

Compaction Table

Removing the shear rings from the water chamber in the machine is handled easily. The shear rings are pulled onto the two compaction table rollers that allow the assembly to slide easily into and out of the water chamber. Preparation and compaction of the sample or geotextile can be accomplished on the table. The table is then rolled back into position for sliding the shear boxes into the water chamber. When removing the shear boxes, it is advised to lock the brakes on the castors.

Construction

The direct shear is designed for harsh lab environments. All steel parts are powder coated and aluminum parts are hard coat anodized for corrosion resistance. Some parts are made from stainless steel.

Click to view a PDF file of the User Guide