Influence of rock mass properties on TBM penetration rate in Karaj-Tehran water conveyance tunnel

Abstract

Predicting penetration rate (PR) of tunnel boring machine (TBM) due to the properties of rock mass surrounding tunnel has been an important subject in the mechanized method of excavating tunnel. Influence of uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), peak slope index (punch penetration), spacing of discontinuities (of weakness planes), orientation of discontinuities with respect to the tunnel axis (β angle) on penetration rate of TBM was investigated while excavating Karaj-Tehran water conveyance tunnel by a double shield Herencnesht TBM. Statistic analysis was carried out on the relationship between measured test results of the five different parameters of rock mass properties and the penetration rate of TBM. The results showed that each of the five different parameters of rock mass properties individually has affected the penetration rate of TBM. The relationship between peak slope index (PSI) and penetration rate of TBM has the best correlation coefficient (r) of 0.57 in comparison with the four others relationship between rock mass properties and the penetration rate of TBM. The relationship between BTS of rock and PR of TBM has a very poor correlation coefficient (r) of 0.11. Multilinear regression analysis was applied to indicate the combined influence of the five different rock mass properties on the penetration rate of TBM using a database of measured test results. A new empirical formula was achieved to predict PR of TBM as a function of different rock mass properties (r = 0.75). Key words: TBM, penetration rate, rock mass properties.