Abstract: Resonance column and bender element are the two most promising methods for obtaining the dynamic small-strain parameters of soils in the laboratory conditions. However, as they are independent systems, tests that combining with their complementary functions have not been reported. This paper presents a new development of using commercial Stokoe type resonance column instrument by GDS (Geotechnical Digital Systems) Company and the implementation of the bender element system into the resonance column test system. The improved device could perform the combined tests on a soil sample. In order to test the reliability of the improved system, the small strain tests on silty sand samples from the Hangzhou Bay were conducted to measure the dynamic modulus. Results show that the device combines advantages of both the resonance column system and the bender element system; for the same sample, the calibration on bender elements can be achieved by the resonance column system, which effectively overcomes the problem of shear wave propagation time determination during the bending element test. There are significant dispersion properties in the bending element tests of the dry sand; when the bending element excitation frequency can satisfy the condition, 2<ξ<7, the influence of the near-field effect can be weakened, and a stable and clear shear wave receiving signal can be obtained.

Key words: resonant column, bender element, triaxial tests, small strain