Ground force analysis of a portable electromagnetic seismic vibrator for different surface environments and driving voltages

Abstract

Knowing the actual ground force is important for seismic data processing and seismic vibrator control. However, the weighted-sum method is widely used to estimate the actual ground force in seismic vibrator exploration. Due to the nonideal body of the baseplate and the nonlinear coupling between the baseplate and the ground, the weighted-sum method suffers from estimation error. It is feasible to obtain the actual ground force by using load cells. In previous studies, the effects of different surface environments and driving voltages on the actual ground force were rarely analysed. In this paper, a field experiment was conducted to study the actual ground force of a portable electromagnetic seismic vibrator for different surface environments and driving voltages. The fundamental wave, multiple harmonics, phase distortion, response delay, weighted-sum method estimation error and ground impedance were analysed.The experimental results show that there are obvious second-to-fifth harmonics in the actual ground force. An increase in the driving voltage will enhance the energy ratio of the fundamental wave, suppress the phase distortion and increase the response time of the actual ground force. In a soft soil environment, there are obvious amplitude and phase differences between the weighted-sum ground force and the actual ground force. The phase difference is affected by the driving voltage, which causes a time delay in the cross-correlated wavelet between the weighted-sum ground force and the actual ground force. The ground impedance beneath the baseplate is highly non-linear. As the vibration frequency increases, the viscosity and stiffness of the coupled ground tend to be stable.