Effects of Vibration on Buried Structures from the Removal of Steel Casings during the Installation of Rockfill Columns for Riverbank Stabilization: A Case Study

Rockfill columns, also known as stone columns, were installed in a riverbank for slope stabilization measures. The goal of this fieldwork was to prevent slope instability of the riverbank while protecting an in-service aqueduct buried in the riverbank. At this site, rockfill columns were installed with the aid of steel casings (sleeves), which were later removed with a vibrodriver. Peak particle velocities were determined at select locations to monitor the ground vibrations during installation of rockfill columns and during extraction of the steel casings. Instrumentation and monitoring were implemented because there was uncertainty about the potential for structural damage to the nearby aqueduct due to ground vibrations during the stabilization works. In this case study, numerical modeling, calibrated versus field measurements in the ground and on the aqueduct, was used to simulate the ground vibrations due to the installation of three rockfill columns close to the aqueduct. Once calibrated, the numerical models were used to evaluate the effects of vibrations in terms of particle velocities in the ground, displacements of the aqueduct, and frequency spectra on the aqueduct walls. The numerical results showed that the highest particle velocities on the aqueduct were from the rockfill columns that had the steel casings located in the same soil layer as the aqueduct. Based solely on the response in terms of particle velocity, damage to the aqueduct is unlikely. However, the numerical results also showed that the aqueduct moves slightly, both vertically and laterally due to the vibration generated while removing the steel casings; and the frequency range of the waves in the ground are within the natural frequency of the soil, which could impose additional movement to the aqueduct if allowed to move freely with the soil. Numerical results and field data also show that even pulling the steel casings without vibration generated propagation of waves in the ground.