Monitoring and Process Control of Deep Vertical Vibratory Compaction Using Resonance Amplification

Abstract

Compaction trials using deep vertical vibratory compaction in a hydraulic fill are reported. The compaction system consisted of a vibrator with variable frequency and a flexible, double Y-shaped probe. Openings in the probe reduced the dynamic weight and enhanced the probe-ground interaction. The compaction process was documented by a monitoring and process control system. The dynamic ground response was measured during different phases of the compaction process by sensors on the compaction machine and in the ground. Ground vibrations were amplified by adjusting the vibrator to the resonance frequency of the vibrator-probe-soil system. Cone penetration tests with pore water pressure measurements were performed before and after treatment, and showed a significant increase in both cone and sleeve resistance. Geophones were installed on and below the ground surface to record vertical and horizontal ground vibrations. The magnitude of horizontal ground vibrations was measured at two distances from the compaction probe, making it possible to determine vibration attenuation. The vertically oscillating compaction probe generated vibrations in both vertical and horizontal directions. Strong horizontal vibrations were emitted during resonance, which can explain the permanent increase in horizontal stress. The increase in horizontal stresses is about twice that of static horizontal stresses. As a result of vibratory compaction, a stress gradient of horizontal stresses is created, which is likely to equalize with time.