Influence of rock brittleness on TBM penetration rate in Singapore granite

Brittleness is one of the most important rock properties, which affects the rock fragmentation process induced by TBM cutters, and then the TBM penetration rate. This paper presents the different measurements of rock brittleness. The ratio of uniaxial compressive strength to Brazilian tensile strength was adopted to quantify the rock brittleness. By the laboratory tests, the brittleness indices of more than 100 samples cored in Bukit Timah granite along the tunnel alignments of T05 and T06 tunnels of DTSS in Singapore were obtained. The brittleness index varies in a large range from less than 10 to more than 25. The tendency shows that the brittleness index decreases with the increase of the weathering grade of granite. A series of models were then set up to simulate the effect of rock brittleness on rock fragmentation process using UDEC. With the decrease of the brittleness index, the crushed zone decreases and the number and length of the main cracks outside the crushed zone also decrease. It is obvious that with the increase of the rock brittleness index the cutter indentation process gets easier. Through the statistical analysis of correlation between rock mass properties and the corresponding TBM performance in tunnel projects, it was noted that TBM penetration rate increases with increasing rock brittleness, which is consistency with the numerical simulation results.