The analysis of laboratory bender element tests has recently been simplified following the launch of a new software tool by GDS Instruments. The GDS Bender Element Analysis Tool (GDS BEAT) was developed to address the subjectivity often present when analysing the data obtained from these tests.
“We found that while bender element systems are increasingly used to estimate the stiffness of a soil test specimen, there are still no well-defined standards for interpreting the data,” says GDS Instruments managing director Karl Snelling. “Currently if two engineers look at the same bender element test data, the conclusions they draw will often slightly differ due to their own subjectivity and a lack of a common procedure for analysing the response.”
The bender element test has been used in a variety of laboratory systems since the late 1970s, including the triaxial cell and resonant column.
The test itself consists of two piezoelectric elements protruding a small distance into the top and base of a soil specimen, with a shear wave generated by one element, and the other used to measure the soil response. The time taken for the shear wave to propagate through the soil, along with the distance between these two elements, can be used to estimate the shear wave velocity. It is the determination of the wave propagation time that is the major cause of subjectivity, and motivation behind sharing the new analysis software.
The GDS BEAT software, which operates in Excel, is user friendly and uses multiple numerical analysis methods. “Ultimately we hope the tool will generate discussion within the larger geotechnical community, and contribute in the progression towards accepted standards for interpreting bender element test data,” says Snelling.