Rock-breaking efficiency of TBM based on particle-size distribution of rock detritus

The shape, particle size and its distribution of rock detritus are the key indexes to reflect the rock-breaking efficiency of TBM, and the important internal link between TBM tunneling parameters and rock properties as well. According to the rock-breaking mechanism of disk cutter, dimension measurements and sieving tests on the rock detritus cut by TBM are carried out, and the dimension characteristics and particle-size distribution of rock detritus are obtained. The statistic analysis and theoretical distribution function fitting are conducted based on the in-situ measured data of dimension and particle-size distribution of rock detritus. The relationships among coarseness index, strength and wear resistance index of rocks are analyzed. The variation laws of coarseness index with tunneling thrust under different surrounding rock classes are discussed. The research results show that the ratio of long axis to short axis of the rock chips is about 1.5, while that of long axis to thickness of the rock chips is quite different for diverse surrounding rocks. The probability distributions of rock chip dimension including long axis, short axis and thickness are subordinate to normal distribution. The particle-size distribution of rock detritus accords with that of Rosin-Rammler function under different rocks. The larger the coarseness index, the higher the rock-breaking efficiency of TBM. The coarseness index of rock detritus decreases with the increase of the uniaxial compressive strength of the rock under hard surrounding rocks, while the change law is contrary for the mid-hard and soft surrounding rocks. The coarseness index of rock detritus decreases with the increase of the wear resistance index of rocks whether the surrounding rocks are hard or soft. The stronger the wear resistance of rocks, the lower the rock-breaking efficiency of TBM. The rock-breaking efficiency of TBM is closely related to the classification of the surrounding rocks. According to the particle-size distribution law of in-situ measured rock detritus, the tunneling thrust intervals when the rock-breaking efficiency of TBM is optimal can be determined under the surrounding rock class II and III.