Effect of some geotechnical properties on TBM performance

Predicting excavation performance of any mechanical miner used in tunnelling and mining industries is very important for decision makers in especially feasibility stage, since it affects whole economics of the project. Among the parameters affecting performance of mechanical excavation systems, geological and geotechnical properties are the basic input for designing a project. Kartal-Kadikoy Metro Project is a big construction project being performed in Istanbul. An earth pressure balance tunnel boring machine (EPB-TBM) with 6.57 m diameter is used for excavation. This study summarizes some of the results of a research on the effects of some geotechnical parameters on performance of the TBM used in Kartal-Kadikoy Metro Project in a selected area. Chunk samples obtained from different rings in the area between Unalan and Ibrahimaga Stations along the alignment were first tested for defining point load index. Then, the uniaxial compressive strength values obtained from point load tests are correlated with TBM operational parameters such as torque, thrust, specific energy, as well as penetration rates. The results indicate that there is a moderate relationship between uniaxial compressive strength (UCS) and penetration index, which is defined as TBM thrust force per millimeter of penetration per revolution of the cutterhead. However, no other relationships could be found between UCS and TBM performance parameters, showing that UCS is not enough to predict the performance of TBMs in fractured rock masses. Predictive models should include also an additional parameter indicating rock mass fractures.