Abstract: Rock chips are the direct product of rock-machine interaction, and are also often used to evaluate tunnel boring machine (TBM) rock breaking efficiency and optimize TBM tunneling parameters. In-situ sieve tests of rock chips for different lithologies were conducted based on Lanzhou water source construction project and Longyan Wan’anxi water diversion project. The particle size distribution was obtained. From the perspective of energy conversion of disc cutter rock-breaking, a novel evaluation index of TBM rock-breaking efficiency based on newly added surfaces theory was proposed. Based on the particle size distribution and the statistics of TBM tunneling parameters, the correlations among the index of newly added surfaces theory, specific energy and coarseness index were investigated. The advantages of the index of newly added surfaces theory in reflecting the fragmentation degree of rock chips and accurately evaluating the rock-breaking efficiency of TBM were clarified. The regression analysis was carried out to examine the correlation between the newly added surfaces theory index and TBM tunneling thrust, the ratio of disc cutter spacing to penetration (s/p), the optimal tunneling thrust force and s/p value range of TBM under the conditions of hard rock (grade II surrounding rock) and soft rock (grade III surrounding rock) were obtained respectively. The research results showed that the index of newly added surfaces theory not only conformed to the principle of rock fragmentation, but also evaluated the rock-breaking efficiency of TBM accurately. The more broken the rock chips, the larger the index of newly added surfaces theory, and the higher energy consumption of the TBM. At this time, the rock breaking efficiency of TBM is relatively low. The index of newly added surfaces theory has a good linear correlation with specific energy and coarseness index. The more broken the rock chips, the more energy consumption of the TBM. The larger the index of newly added surfaces theory, the smaller the coarseness index. Under the condition of soft rock, the specific energy of TBM tunneling is lower than that of hard rock, however, the fragmentation degree of rock chips is higher than that of hard rock. The index of newly added surfaces theory decreases first and then increases with the rise of tunneling thrust and s/p. Under the conditions of hard rock and soft rock, when the optimal tunneling thrust interval and s/p interval of TBM are 7 400−7 700 kN, 13.9−14.4 and 1 000−1 500 kN, 8.0−8.5 respectively, the index of newly added surfaces theory is small and the rock breaking efficiency of TBM is high.

Key words: tunnel boring machine (TBM), rock chips, energy conversion, newly added surfaces theory, coarseness index, specific energy, tunneling thrust, the ratio of disc cutter spacing to penetration (s/p)