CORRELATING BENDER ELEMENT AND ELECTROMAGNETIC MEASUREMENTS TO EVALUATE CLAY’S STIFFNESS

Abstract

Soil’s stiffness is usually measured in the laboratory in an indirect manner, such as by
derivation from the gradient of a stress-strain plot. It requires numerous tests and may be compounded by
errors from the original measurement itself. As such, the bender element test has become rather popular
among researchers for determining the small strain moduli of soils with minimal / temporal disturbance to the
specimens. This paper examines the possibility of relating the bender element data with the dielectric
constant obtained from the same soil specimen using an electromagnetic test setup. As both tests are nondestructive, they can be easily repeated on the same specimen over a period of time without the necessity of
duplicate specimens. A clay sample was used in the present study, with varying water content corresponding
to different 1-dimensional compression stresses. It was generally found that the resulting stiffness change
was detectable from both the shear wave velocity (vs) obtained from the bender element tests, as well as the
dielectric constant (ε) of the electromagnetic measurements, with fairly good correspondence between the
two. These results shed light on the possibility of relating relevant geotechnical parameters with both the
measurements for establishing a unique set of signatures for stiffness monitoring and determination in soils.