Installation and Instrumented Load Testing of Deep Soil Mixing Columns

Due to very poor upper soil conditions, it was elected to support the process plant facilities for a Liquefied Natural Gas Plant owned by Atlantic LNG in Trinidad on a grid of Deep Soil Mixing (DSM) columns. The DSM columns, which were generally constructed in a grid pattern under all foundations, were installed from the ground surface down to the underlying hard, clayey soils, generally referred to as the Old Marine Sediments (OMS). The depth to the OMS was typically 10 to 12 meters. The DSM columns were installed using instrumented triple-shaft drilling equipment. During the entire installation process real-time measurements were taken and recorded regarding depth of penetration, penetration and withdrawal speed, shaft rotation speed, and slurry injection rates. Also recorded during installation was the energy measurement and what was referred to as the tool-bar loading. The energy measurement in combination with the tool-bar loading was used to verify that the DSM had penetrated into the underlying OMS as required by design. The load testing of the DSM columns was performed to both verify the quality of the installation procedure and to confirm the actual settlements of the mat foundations constructed on the DSM columns would be within predicted levels. It was also elected to perform an instrumented load test of the DSM column in an effort to determine both the vertical and horizontal stress distribution through the column.