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The energy injected virtual mass (EIVM) resonant column maintains the amplitude of the soil sample by continuously replenishing energy, thereby calculating a more accurate damping ratio.

The traditional resonant column method for measuring shear modulus is consistent with the EIVM resonant column, which is obtained by measuring the shear wave velocity. However, there are two methods for measuring the damping ratio of the traditional resonant column. One is the half-energy bandwidth method: by obtaining the relationship between amplitude and frequency, the resonant frequency under the current shear strain and the frequency when the energy is half of the resonance are obtained, as shown in Figure 1, and the damping ratio can be obtained by formula (1-1).

Figure 1 Amplitude-frequency response diagram

(1-1)

Another method is the free oscillation attenuation method, which obtains the amplitude attenuation curve when a certain amplitude stops vibrating, as shown in Figure 2, and then calculates the damping ratio according to formula (1-2).

Figure 2 Amplitude-time decay diagram

(1-2)

The half-energy bandwidth method will generate a lot of vibration to the soil sample when obtaining the amplitude-frequency response diagram, which will reduce the damping ratio. Since the amplitude of the free oscillation attenuation method is constantly decaying, there is no analytical solution for the shear strain corresponding to the measured damping ratio. In experience, the average value of the amplitude from the first to the third cycle is often taken. This is a shortcoming of the traditional resonant column when measuring the damping ratio. The EIVM resonant column measures the damping ratio by applying a torque to the soil sample to keep it vibrating with equal amplitude. The damping ratio of the soil can be calculated through the torque. The measured damping corresponds to a clear shear strain, and there is no pre-vibration that makes the damping ratio smaller.