AIMS Array Design and Construction

This paper discusses the design and construction of the U.S. NAVY's first Assessment and Identification of Mine Susceptibility (AIMS) array to be installed on the seabed in a near shore exposed open ocean environment. The AIMS array structure supports sensors which aid in calibration and prepare the U.S. NAVY's mine countermeasure (MCM) ships for missions. To accurately measure acoustic and magnetic signatures utilized in calibration of these specialized ships, the AIMS array sensors were required to have limited movement and vibrations. The MCM fleet was recently relocated from Ingleside, Texas to San Diego, California as part of the Base Realignment and Closure Commission recommendations of 2005. Calibration of the recently relocated MCM fleet required design and construction of the AIMS array structure be completed in an accelerated 14-month project schedule. The preferred design consisted of a trapezoidal-shaped structure, 114 feet (34.8 m) long by 20 feet (6 m) wide by 16.5 feet (5 m) tall with eight 3-foot (0.9 m) diameter pipes extending above the top of the structure. Strict design criteria required the supported sensors to have limited movement and vibrations under operational waves and that the structure be able to survive a 33-foot-high (10 m) near-breaking wave. All materials were required to be nonmagnetic and nonmetallic. To achieve the design requirements, four 273,000-pound (123,830-kg) precast caisson modules were designed utilizing fiber-reinforced polymer (FRP) reinforcing bars. The well-thought-out and detailed design founded on conservative design principles, allowed flexibility during construction and proved instrumental in meeting the project requirements and schedule in the open ocean environment, where swells often exceeded 5 feet (1.5 m). Construction and installation of the AIMS array structure required the contractor to develop an aggressive schedule with multiple crew shifts. A local precast concrete manufacturer constructed the concrete elements reducing onsite construction time and increasing quality control. This, however, required multiple, complex, heavy-lift operations to transport and install the caisson modules. Installation of the modules was completed utilizing one of the largest floating derrick barge cranes on the West Coast. Upon completion of construction, acceptance testing was completed confirming that the construction and AIMS array successfully met the U.S. NAVY's operational requirements.