Instrumentation for Vibro Stone Column Soil Improvement

Abstract

The Vibro stone column treatment method is widely used for site liquefaction mitigation. Today, the quality control of stone column installation includes the monitoring, recording, and displaying of vibrator penetration depth, energy consumption, gravel consumption, and air pressure to continuously aid the operator and the inspector. In the past 15 years, with the advance of electronic and computer technology, the data acquisition and data recording system for the vibro stone column construction has been developed and widely used in many projects involving the authors. The need for improving the quality of construction led the development of the iVibro system, an integrated instrumentation system using TCP/IP based data acquisition technology, wireless communication, graphical user interface, and GPS satellite navigation and gyro technologies for accurate underwater construction. Given the real-time display and comprehensive data, the design geotechnical engineer can better analyze the site response and evaluate the effectiveness of vibro stone column treatment. This paper covers the vibro stone column instrumentation for several projects, including the Mount Hermon and BART (Bay Area Rapid Transit) marine test section projects. The marine project involved the installation of stone columns in over 90 feet of water and only 1.52 meters (5 feet) away from the San Francisco – Oakland trans bay subway tunnel. BACKGROUND Vibro-compaction is a soil improvement technique that uses a specially developed depth vibrator to direct compactive energy throughout the required improvement depth. Improvement is achieved by rearranging the soil matrix to a tighter packing, resulting in an increase in the in-situ density and shear strength of the soil mass. Vibro-replacement/displacement uses the same depth vibrator; however, it also introduces gravels to fill the void caused by the vibro densification. Therefore, the vibro- replacement/displacement method is often referred to as the Vibro Stone Column technique. These Vibro soil improvement methods are widely used for site liquefaction mitigation, increasing foundation bearing capacity and settlement reduction, roadway embankment foundation reinforcement, and slope stabilization. Quality control is one of the key factors of a successful Vibro project. In the 1930s, during the early development stage, operators used volt and current meters to measure the vibrator power consumption. They also measured the volume of sand backfilled