Smartbolt wins award

Mintek has designed and developed an innovative safety monitoring device to warn of changing mine roof conditions. For the development of this innovation in mine safety, the SmartboltÔ, Mintek has won a coveted SABS 2005 Prototype Award.

The Smartbolt is installed alongside conventional steel rock bolts in mine roofs for added protection and safety underground. Rock engineers can measure changes in sound velocity in the bolt, using an ultrasound monitoring device. Information can be gathered and logged quickly to determine whether any bolts have been bent, broken or overloaded. Furthermore, if a Smartbolt was located in an area that collapsed, and could be recovered, it would also be possible to determine the extent of damage from the information that was recorded earlier, prior to the rock fall.

When stressed, this metastable bolt undergoes a microstructural transformation. Depending on the degree of loading, the bolt’s properties will change from non-magnetic to magnetic, resulting in a change in longitudinal sound velocity, which warns of changing mine roof conditions. The Smartbolt will enable rock engineers to anticipate and record rock movement.

A portable ultrasonic (USM 25 DAC) monitoring device measures sound velocity along the length of the bolt. Its probe is applied to the head of the Smartbolt, allowing monitoring of changes in the microstructure that results from the stresses exerted on the Smartbolt by changing roof conditions.

An additional attribute of the Smartbolt alloy is that its chemical composition allows it to function in mines with highly corrosive water. Also, results from the characterisation programme also show that the Smartbolt alloy has a good combination of high strength and durability. This makes it a suitable sensor candidate for extreme conditions of high tensile and shear stresses, similar to conventional roof bolts.

The Smartbolt is interrogated by portable ultrasonic USM 25 DAC device which measures the longitudinal sound velocity to assess any structural change. The probe is applied to the head of the bolt and the sound velocity feedback is used to assess microstructural changes that have occurred in the bolt as a result of the stress exerted on it.