Bender Element Testing
A test that can aid in predicting soil and foundation response to seismic and manmade disturbances is covered in a proposed new ASTM International standard. The proposed standard, WK23118, Test Method for Determination of Shear Wave Velocity by Bender Element, is being developed by Subcommittee D18.09 on Cyclic and Dynamic Properties of Soils, part of ASTM International Committee D18 on Soil and Rock.
Thomas Sheahan, professor and acting chair, department of civil and environmental engineering, Northeastern University, notes that a significant challenge to characterizing ground mechanical properties (such as the ability to support foundations) is obtaining representative samples from the ground to test in the laboratory.
“As we sample and transport the soil, its structure is compromised, so by the time we test it in the lab, it may not imitate the field properties very well,” says Sheahan, a D18 member. “By performing bender element tests and comparing these results to field test results, the degree of structure compromise can be determined.”
In addition, determining stiffness by bender elements allows for advanced computer modeling of systems such as foundations and retaining walls.
According to Sheahan, WK23118 will fill a needed role for laboratories. “An increasing number of testing laboratories are using bender elements to determine small strain shear modulus, and there is no existing standard to guide test procedures,” says Sheahan. “This proposed standard will fill an important gap in available testing methods guidance.”
Sheahan says that interested parties with experience in bender element testing are welcome to assist in the further development of WK23118. The subcommittee would like to hear about equipment and procedures (particularly analysis methods) used in bender testing.
Technical Information: Thomas Sheahan, Northeastern University, Boston, Mass.
ASTM Staff: Robert Morgan