A new portable smart device will help engineers determine the structural condition of bridge foundations situated underwater.

Diagnosing the structural health of a bridge is extremely difficult for engineers, given that bridges' foundations are not just embedded below the earth, but beneath riverbeds obscured by bodies of water.

While trained divers are usually the only expedient available to engineers hoping to determine the condition of submerged bridge foundations, researchers from the Missouri University of Science and Technology (MUST) believe they may have found a better and cheaper solution with the development of what they refer to as "smart" rocks - devices which contain magnetic or electronic components that are capable of relaying data on erosion damage.

One of the chief causes of bridge collapse is scour, an erosion process in which the passage of water - particularly during flood events - creates hollows around bridge piers or abutments by removing riverbed material, resulting in an unstable foundation. In the United States alone, around 60 per cent of bridge collapses can be imputed to hydraulic factors, in which scour plays a significant role.

The smart rocks developed by the MUST scientists are capable of measuring the progress and extent of this scour process. The devices are placed adjacent to the base of bridge foundations, in prime position to role to the floor of any scour holes that are created by water erosion. Once at the bottom of the scour holes, they can transmit vital data about them, such as their depth and number, back to engineers.

The researchers have thus far developed three different smart rocks for transmitting erosion-related information. The simplest version is a passive smart rock which contains an embedded magnet and which must be read by means of a remote magnetometer.

smart rock

The semi-active smart rock represents a step up, containing a free-to-rotate magnet which can be remotely controlled using electronic circuity, while the apogee of the technology is the active smart rock, which contains a complex panoply of instruments, including a pressure sensor, gyroscope, timer, battery indicator and individual identification, and is capable of relaying data by wireless communication.

This range of technology makes the smart rock versatile, enabling engineers to access the different types of data they may require depending on circumstance.

During regular weather conditions, a reading is only required once every six months to a year, but should frequent or heavy flooding occur, the active smart rock can provide more detailed information on the progress of erosion so engineers can monitor the state of bridge structures with heightened accuracy.

The smart rocks are close to indestructible, while their batteries enable them to operate for periods of between five years to a decade, depending upon their frequency of usage.

The researchers have already tested the smart rocks at the Gasconade River Bridge and Roubidoux Creek Bridge in Missouri in 2012 with positive result, and hope to cooperate with the state departments of transportation to conduct further testing during flood seasons in other areas.