A New Method of Quality Control for Jet Grouting Online Vibration Monitoring-Paper

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The paper presents vibration monitoring as a new quality-control method for jet grouting, addressing a limitation of conventional practice: repeating test-column construction parameters cannot reliably account for changing soil conditions or confirm the actual column diameter and overlap.<br /><br />A jet-grouting beam generates vibrations as it erodes and mixes soil. Once hardened, a column can transmit these vibrations along its axis. Sensors installed in standpipes record the acceleration produced when a new column is jetted nearby. Processing the signals with filtering and Fast Fourier Transform (FFT) techniques helps distinguish contact with hardened columns from energy dissipated in soil. The vibration peaks also indicate rod rotation, beam contact time and contact angle, from which column radius can be estimated.<br /><br />Field tests in Berlin compared calculated column dimensions with measurements made after excavation and found close agreement. Further tests on a construction project showed that signal profiles can distinguish no contact, partial contact, regular overlap and oversized secondary columns. These patterns can help assess the interlock between primary and secondary columns in watertight slabs.<br /><br />The method can monitor columns below ground without excavating them and can be applied during construction. Reusable sensors can be placed at selected points along a primary row. The authors conclude that vibration monitoring can support assessment of column diameter and overlap, and may be useful for larger structures such as metro stations and tunnels. Signal intensity can vary because jetting is turbulent, so interpretation relies on characteristic patterns rather than peak magnitude alone.

Keywords

jet grouting

vibration monitoring

quality control

column diameter

column overlap

Fast Fourier Transform

signal filtering

soil conditions

beam contact

watertight slabs