ROCK MECHANICS
Sigra provides a broad rock mechanics service that spans the needs of underground coal and metalliferous mining to open cut and civil engineering.
Field Measurement Services
Sigra's rock mechanics field services start with its in-situ stress measurement tool (IST). This is the most advanced biaxial overcore stress measurement system in the world. It operates in conjunction with Boart Longyear HQ wireline drilling equipment and can be used to measure stress at depths up to 1500 m. The equipment is compact, weighing 180 kg and can therefore be airlifted into site. The tool is suitable for hard or soft rock operation. The method by which the tool is used is described in the paper "The Measurement and Interpretation of Stress", from the 2000 Bowen Basin Symposium.
A photograph of the tool is shown in photograph P1 and an overcore trace is shown in drawing D1 and the resultant best fit to the measured deformations is shown in drawing D2 along with the calculated stress level.
P2 shows the stress tool in a core, whilst P3 shows the tool next to the same core. P4 shows drilling tools belonging to the IST system.
As well as measuring in-situ stress Sigra can supply and fit triaxial and uniaxial stress change cells. These are grouted in devices and these can be supplemented by strain or displacement measurements.
Fluid pressure be it liquid or gas can also be monitored either using grouted-in-place or packer sealed pressure sensors.
Sigra can provide in-situ thermal conductivity measurement of rocks from a borehole. This is achieved by isolating a section of borehole with packers and heating the isolated section with a known electrical power for a set interval. The power is then turned off and the temperature recovery is measured. Analysis of temperature rise and decay provides thermal conductivity information.
All long term field monitoring is via Sigra's field data acquisition systems. The field data logger with its radio or cellphone link enables data to be transmitted back to the office worldwide while the two wire system permits multiple sensors to be attached to two wires. The latter is ideally suited to borehole or underground operations.
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Consulting
Sigra can provide rock mechanics expertise to slopes in open cut mines or to road cuttings. Rock anchor and drainage design are a speciality as are the control of boulder fields. Its consulting expertise is backed by extremely good field monitoring equipment.
In the underground environment Sigra can provide good advice in tunnelling, coal or hard rock environments. The company's flair for inventing systems and techniques can lead to useful designs such as the cable anchoring system to support longwall recovery roads shown in drawing D3. In-house knowledge of the design and use of packers and high pressure water pumping systems makes the company an ideal consultant in the deployment of hydrofracture based rock excavation systems.
Sigra has expertise in the grouting systems that is particularly relevant to the stabilization of rock masses.
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Equipment
Sigra supplies monitoring equipment and packers for grouting or hydrofracture based excavation.
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Research and Development
Sigra is an inventive company with a good base in rock mechanics. It is capable of arriving at novel solutions to problems. This problem solving is assisted by its in house mechanical and instrumentation capability. For example new rock support systems can be designed, prototypes built and their installation monitored by in house capabilities.