GDS commercializes variable direction dynamic cyclic simple shear device; revolutionizes commercial simple shear testing

GDS recently launched its Variable Direction Dynamic Cyclic Simple Shear ((VDDCSS). The Simple Shear loading has numerous applications in practice, such as seismic loading scenarios (Pestana and Biscontin 2000), shearing of soil during pile loading in compression (or extension) (Randolph and Wroth 1981), slope stability (Ladd, 1991) and even experimentally simulating stress conditions below a rolling wheel (Shaw and Brown 1986). Simple shear has been the subject of extensive research and has been also used extensively in practice.

The Variable Direction Cyclic Simple Shear (VDDCSS) represents a major step forward in the development of commercial cyclic simple shear devices as it allows simple shear to be performed in two directions, rather than the standard single direction. This is achieved by having a secondary shear actuator that acts at 90 degrees to the primary shear actuator. The development of the device is very timely. For years, such capabilities were available only in research labs and were not readily available. These recent research studies have shown that variable direction testing is needed to provide a more realistic representation of the types of loading that soils are subjected to.

During earthquakes for example, seismic shaking is never one directional, and in most projects of interest there is an initial shear stress in the vertical and horizontal planes. In offshore projects, this becomes a critical consideration, for submarine landslides that can threaten offshore oil platforms and other infrastructure. Wind farms are also taking advantage of wind loading to generate power, but, as a consequence, their foundations are subjected to a complex, oscillatory, movement that cannot be fully represented by a conventional simple shear.

The secondary shear axis of the VDDCSS can be used independently of the other shear axis or in conjunction with it, therefore simple shear may be performed in any horizontal direction. Tests can be carried out with constantly rotating shear vectors. The device can also be combined with bender element testing to provide a reliable assessment of the shear wave velocity and small-strain shear modulus.

Technical specifications of the device include:

Actuators: 3 x electro-mechanical, high accuracy, encoder controlled actuators

Axial Force Accuracy: Typically <0.1%

Axial Load (kN): 5

Displacement Range:

Shear axis +/- 10mm (+/-30% shear strain)

Normal axis +/- 25mm (+80% consolidation strain)

Displacement Resolution: 0.3μm

Load Range (kN): 5 normal force, 2 on each shear measurement (y and z)

Operating Frequency (Hz): 1

Sample Size (mm): 50 diameter specimen, height 20 to 30 (other sizes on request)

The device communicates with PC via USB and has a user-friendly user interface. More information can be found in this datasheet:

http://gdsinstruments.com/__assets__/products/000110/VDDCSS%20datasheet.pdf?utm_source=Geo-engineer&utm_medium=news_vddcss&utm_campaign=Geo

The GDS website with information on this simple shear device is available here:

http://www.gdsinstruments.com/gds-products/variable-direction-dynamic-cyclic-simple-shear?utm_source=Geo-engineer&utm_medium=news&utm_campaign=geo

References:

Ladd, C.C. (1991). "Stability evaluation during staged construction: 22nd Terzaghi Lecture." Journal of Geotechnical Engineering, ASCE, 117(4), 537-615.

JM Pestana, J. M., Biscontin, G., Nadim, F., Andersen K., (2000) "Modeling cyclic behavior of lightly overconsolidated clays in simple shear." Soil Dynamics and Earthquake Engineering 19 (7), 501-519

Shaw, P., Brown, S.F. (1986) "Cyclic Simple Shear Testing of Granular Materials." ASTM Geotechnical Testing Journal, 9 (4), 213-220.

Randolph, M.F. and Wroth, C.P. (1981) "Application of the Failure State in Undrained Simple Shear to the Shaft Capacity of Driven Piles." Geotechnique, Volume 31, No. 1, pp 143-157