Workability: The installation of piles using suction caissons can be achieved using low- cost vessels to deploy the caissons and operate the pumps. Also, depending on depth, the pile lowering may also be achieved using auxiliary buoyancy to minimize pile heave and motions caused by surface waves and weather. Leveling, Batter Installation: A simple modification of the annular suction caisson creating multiple pressure chambers allows the individual sections to be pressurized individually, to level the caisson. The leveling feature would require remote inclination data and pump or valve control from the surface vessel. An adaptation of this partitioned caisson is to use 3 separate buckets with the driven pile sleeve and gripper constructed at their center. In a similar fashion to leveling, the driving caisson could be programmed to achieve a moderate batter to install battered piles. In this case, bending due to pile stick-up with hammer weight would not apply. Disadvantages Time: Depending on the soil conditions, the suction caisson may have a limited stroke, increasing the time to install a single pile. Shallow Water Capability: The pressure differential required to drive the pile to the target depth is less in shallow water; therefore, the technique may not be ideal for use in such situations. Liquefiable Soils: Loose soils may not be suitable, or well-suited for economic use of this technique. If suction is applied at an excessive rate, loose sands may liquefy, decreasing the effectiveness of the technique and causing excessive soil heave inside the caisson. Maneuverability: Installing closely- spaced piles may prove problematic for this technique due to interference caused by the suction caisson, which requires a large footprint. This problem may be solved by adjusting the suction caisson geometry. Cyclic Soil Strain: The installation scheme repetitively loads and unloads the soils near the surface and along the caisson wall. The effects of this cyclic loading require site-specific review and in some cases, testing to determine the degradation of the soils surrounding the installed foundation. Conclusion Future testing will determine which site conditions, pile and caisson sizes, and water depths will be cost competitive with traditional impact and vibratory driving techniques. We need rigorous research to determine if the pressure differential created by suction will be great enough to overcome the resistance to driving forces inherent with the permanent pile as it penetrates deeper into the ground. The list of authors and companies from which we drew information or images for the article follows: Sangchul Bang, Graham Smith, Jitrada Buacharoen, Mark Randolph, Christophe Gaudin, Susan Gourvenec, David White, Noel Boylan, Mark Cassidy, Aker Solutions, CALTRANS, ICF Jones & Stokes, Illingworth and Rodkin, Inc., Norwegian Geotechnical Institute, StatoilHydro, VSL International LTD 56 • DEEP FOUNDATIONS • JAN/FEB 2013
