Analysis of TBM tunneling performance based on mass fractal dimension of rock chips: Fid-Bau Portal

Analysis of TBM tunneling performance based on mass fractal dimension of rock chips

Yan, Changbin / Gao, Ziang / Gao, Zihe / Chen, Jian / Yang, Fengwei / Wen, Sen

Highlights • The 31.57 km long water conveyance tunnel in Lanzhou, China, and the 27.94 km long diversion tunnel in Longyan, China were selected for investigation. • Tunnel geological investigations, rock chip sample collection and field sieving tests were conducted. • Fractal dimension was used to characterize the mass distribution characteristics of rock chips in different lithology tunneling sections. • The relationship between specific energy, coarseness index and mass fractal dimension of rock chips was verified based on field engineering records. • The optimal thrust force interval of TBM was investigated using mass fractal dimension.

Abstract The size of the rock chips and its particle size distribution can fully reflect the rock-breaking efficiency of the TBM, but the index that can comprehensively characterize the particle size distribution of rock chips has not yet been found to quantitatively evaluate the TBM tunneling efficiency. Based on the fractal theory, this study uses the mass fractal dimension to quantitatively analyze the particle size distribution of rock chips, and explores its relationship with TBM tunneling performance index. Field sieving tests were carried out on rock chips from two tunnel projects. According to the sieving test results, the mass fractal dimension of the rock chips is calculated as well as the correlation between it and common TBM performance evaluation indexes, average tunneling thrust is discussed. The research results show that the mass distribution of TBM rock chips has significant fractal and self-similar characteristics, the higher the content of large-size rock chips, the lower the content of small-size rock chips, the smaller the fractal dimension value. Simultaneously, under the same surrounding rock conditions, the mass fractal dimension of rock chips is positively correlated with the logarithm of specific energy and negatively correlated with the logarithm of coarseness index, which indicates that the smaller the fractal dimension, the higher the efficiency of rock breaking. It is demonstrated that the interval of TBM thrust force corresponding to smaller specific energy, larger coarseness index and smaller fractal dimension is the same, which can be determined as the optimal thrust interval.