Ground vibration characteristics of carbon dioxide phase transition fracturing: an in situ test

Carbon dioxide phase transition fracturing is a safe rock-breaking technique. Its vibration effect cannot be ignored. It is valuable for fracturing safety control to investigate its ground vibration characteristics. In this paper, a single-hole test was implemented, and several vibration curves in jet direction and vertical jet direction were monitored to explore the ground vibration difference in these two directions. The attenuation laws of the peak particle velocity (PPV) and the Fourier dominant frequency were obtained. Moreover, based on the Hilbert–Huang transform method, the time–frequency–energy characteristics for the fracturing vibration were evaluated. The test results indicated that the PPV in jet direction is higher than that of the vertical jet direction, and the PPV obeys the power attenuation function in these two monitoring directions. When the explosion center distance increases from 2.193 to 6.067 m, the Fourier dominant frequency fluctuates slightly around 2 Hz in jet direction, but it decays from 12.5 to 1.6 Hz in the vertical jet direction. The vibration signal energies in jet direction and vertical jet direction are both distributed within 0–48 Hz. In addition, it is indicated that the vibration signal energy converses from a high-frequency band to a low-frequency band as the explosion center distance rises from 2.193 to 6.067 m. Due to the significant difference between the ground vibrations in the diverse directions, when this fracturing technique is carried out near the buildings, it is suggested that the installation direction of the fracturing pipe should be considered.