Laboratory Tests on Dynamic Properties of Soils

Laboratory testing skills have been needed to determine

G

/

G

max

and

h

in a small strain range of 10

− 6

 − 10

− 2

(0.0001%–1%). It was, however, difficult in 1960s and 70s to precisely measure the stress-strain behavior in the small strain range (< 10

− 4

approximately). The solution to this problem was the resonant column test.

The method of resonant column test was developed by K. Iida in 1930s. It became popular worldwide since 1950s. Firstly, Ishimoto and Iida (1936, 1937) developed both a theory and a device for resonant column tests on soils, in which the loading frequency at the maximum response was employed to determine elastic properties of soils. Since no confining pressure was able to be applied to consolidate specimens at their times, soil samples with fines and moisture, that could maintain shape without pressure application, were tested. Later, Iida (1938) carried out tests on dry sand which was supported by cellophane sheets. Since no effective stress was applied in these tests, the measured

V

s

, ranging from

V

s

= 50 m/s to

V

s

= 200 m/s, appears to be low.

This testing technique applies cyclic force to a soil specimen at various frequencies. The dynamic response of a specimen to this force is measured in terms of velocity and/or acceleration. While a precise measurement of small displacement (deformation) is difficult, velocity and acceleration at a high frequency are large enough to be measured. By varying the loading frequency, the variation of amplification in amplitude of response is plotted against the frequency. Fig. 10.1 illustrates the testing method conceptually and Fig. 10.2 is an idea of test results.