Rock testing plays a crucial role in the success of Tunnel Boring Machine (TBM) projects. By conducting various tests on rock samples, engineers can assess the rock mass properties and make informed decisions regarding TBM design, excavation parameters, and support requirements.
The most common rock tests related to TBM projects are:
- Uniaxial Compressive Strength (UCS) Test: Measures the rock’s strength under axial loading, providing a basis for TBM selection, cutter wear prediction, and support design.
- Point Load Test (PLT): Evaluates the rock’s strength by applying a concentrated load, providing an estimate of its compressive strength and brittleness.
- Indirect Tensile Strength (aka. Brazilian Tensile Test): Determines the rock’s tensile strength, crucial for understanding its behavior during TBM excavation and support design.
- Shear Strength Test: Measure the rock’s resistance to sliding along fracture planes and provide essential information for stability analysis and support design
Additionally to rock testing, bit wearing testing is crucial in TBM projects as it helps assess the performance and durability of the cutting tools (bits) used in the tunnel excavation process. By evaluating bit wearing, engineers can make informed decisions regarding bit selection, maintenance schedules, and overall project efficiency and cost optimization.
Bit wearing can be estimated in laboratory through the Bit Wearing Index (BWI). BWI consists on three(3) different tests that evaluate the drillability, compaction and abrasion of the rock to be excavated, and their combined effect on the cutting tool.
The BWI is composed by,
- Drillability Index (DRI)
- Siever’s Miniature Drill test (SJ-value)
- Brittleness test (S20 value)
- Abrasion Value (AV) / Abrasion Cutter Steel Value (AVS)
Janc, B. & Jovicic, Vojkan & Vukelić, Ž. (2020). Laboratory Test Methods for Assessing the Abrasivity of Rocks and Soils in Geotechnology and Mining Applications. Materials and Geoenvironment. 67. 10.2478/rmzmag-2020-0012.
Majeed, Yasir & Bakar, Muhammad & Butt, Irfan. (2019). Abrasivity evaluation for wear prediction of button drill bits using geotechnical rock properties. Bulletin of Engineering Geology and the Environment. 79. 1-21. 10.1007/s10064-019-01587-y.