GDS Instruments has released a new advanced soil testing system that was initially developed to better understand the dynamic response of infrastructure in a growing sector of the wind energy market but which the company believes will have wider benefits.
The Variable Direction Dynamic Cyclic Simple Shear (VDDCSS) is designed to deform soil elements statically and dynamically under bi-directional simple shear loadings, enabling soils to be sheared in any horizontal direction.
According to GDS, this development offers expanded test functionality compared with other commercially available direct simple shear devices, whichtypically allow the soil to be deformed along a single fixed horizontal axis. The company says given the extensive use of direct simple shear testing to characterise soil behaviour in practice and during research studies, the VDDCSS offers an exciting prospect for element testing.
To create the VDDCSS, GDS based the hardware design on its EMDCSS, a uni-directional simple shear system - but the main modification is a secondary shear axis located on top of the primary shear actuator, which applies deformation in a direction perpendicular to the primary axis (ie at 90°). The system can operate each horizontal actuator independently or together in tandem, allowing almost any loading pattern in the horizontal plane to be
The driving force behind development of the VDDCSS was a request from the Hamburg University of Technology in Germany. Academics at the university wanted to intensify research into soil behaviour under varying shear directions.
Hamburg University researcher Christina Rudolph says: “The early test results indicate that a pile-soil system possesses a memory of its loading history, including the loading directions. However, it is still unclear how that memory works in detail.”
By using the VDDCSS, Rudolph and her colleagues are able to directly apply cyclic strain or stress paths to a soil specimen with varying direction, while the resultant stresses or strains can be analysed to gain more insight into the nature of soil memory.
“By applying shear forces to a small soil specimen in the VDDCSS, rather than to a laterally-loaded pile, we are able to isolate the soil behaviour fromthe pile-soil system behaviour,” concludes Rudolph.