TDI-Brooks, a company specializing in geotechnical and offshore survey projects, said Wednesday it had developed and tested a new instrument called the Auto-Minivane.
"The Auto-Minivane instrument is a self-contained, stand-alone miniature vane shear testing device that can be used in a 0.5 m vertical-stroke format by an onshore or offshore laboratory. The 1-m-stroke format can be mounted onto a box corer at sea to measure soil strength deep into the box core soil sample," TDI-Brooks said.
According to TDI-Brooks, the new Auto-Minivane accurately and precisely measures the undrained shear strength of very soft to stiff saturated fine-grained clayey soils in an automated process, including its ability to automatically advance down a series of preset depths for successive soil measurements in an acquired box core.
"The tool conforms to ASTM D4648/D4648M-16, and its measurements consistently match those generated with the conventional mechanical tools. Its operation removes essentially all of the unwanted operator error and operator differences from the tests, allowing much better repeatability of results, as well as increased precision and accuracy. It can also be programmed to perform residual strength tests at each depth an undrained shear strength test is performed," TDI-Brooks said.
"The standard miniature vane shear test consists of inserting a four-bladed vane in the end of a remolded soil sample and rotating it at a constant rate to determine the torque required to cause a cylindrical surface to be sheared by the vane. This torque is then converted to a unit shearing resistance of the cylindrical surface area.
"The torque is measured by a torque spring or transducer that is attached directly to the vane. The ASTM methods include the use of both conventional calibrated torque spring units (Method A) and calibrated electrical torque transducer units (Method B), both with a motorized miniature vane shear device. The TDI-Brooks Auto-Minivane tool conforms to ASTM Method B. We have operated this tool side-by-side with conventional Method A tool in our laboratory, testing hundreds of soil samples spanning a comprehensive range of soil strengths, and the results are the same using both devices," TDI Brooks said.