Preliminary study on the weakening effect of microwave irradiation on Singapore Bukit Timah granite and its influence on mechanical excavation performance

The Bukit Timah granite (BTG), which occupies one third of Singapore land area, has excellent engineering properties and is suitable for the development of underground space for various purposes. Microwave-assisted rock breakage has been proven to be a promising method for solving the problems of low operating efficiency and excessive tool wear during mechanical excavation in hard and highly abrasive rock masses. In this paper, the weakening effect of microwave irradiation on BTG and its impact on mechanical excavation performance were studied by laboratory tests and empirical models. The results showed that the longer the microwave irradiation time, the greater the sample mass loss and volume change. Corresponding to the variation of crack characteristic and sample volume, the ultrasonic velocity and UCS of BTG decrease with the irradiation time. The mass change can be explained by the escape of contained water at high temperature, while the weakening mechanism is mainly related to the differential expansion among biotite, quartz and other minerals. Meanwhile, microwave irradiation can also decrease the CAI value of BTG to some extent due to the weakened connection between mineral particles and micro cracks generated in the sample. Prediction on the mechanical excavation performance of roadheader shows that the excavation rate and tool consumption can be greatly improved by microwave irradiation.