DRILL AND BLAST | TECHNICAL


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the advancing face, some 20m back, and even at the face, “without much hindrance to the excavation cycle,” Ødegaard explains. RSRT measures the magnitude of normal stress


action across the fracture being stimulated, or jacked open, during tests and, in principle, provides “an estimate of how much pressure the rock mass can sustain without failing,” he adds. The testing system was developed with, first,


laboratory experiments using a custom-built true- triaxial test rig to allow controlled hydraulic jacking experiments on a granite test specimen. The rock


specimen was hydraulically fractured to create a planar fracture for later testing. Acoustic emission monitoring was used to map fracture geometry and investigate fracture behaviour. With known geometry and controlled stresses, the


test rig enabled development of a testing regime to have the flow increased over a series of equal periods, and then decreased – a controlled and graduated ramping up, and then down. The time-flow steps are to be adapted to local site conditions and then the resulting development of hydraulic pressure measured to map rock-stress behaviour, followed by interpretation of


Above: Onsite tests of RSRT rock stress measurement system SOURCE: ØDEGAARD (2021)


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Pump head


Pressure transmitter Bourdon gauge Electromotor


Pressure relief valve Connection box Accumulator tank


Direction of flow is indicated by small arrows


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Left: Test rig of new RSRT rock stress measurement system


D A C E


SOURCE: ØDEGAARD AND NILSEN (2021)


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A Rigid test frame Hydraulic crane Granite specimen Hand pumps Injection pump


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