Abstract
This paper investigates the optimum penetration depth and the synergistic effect of TBM (Tunnel Boring Machine) rock breaking under the different cutter spacings. Indentation tests, using two TBM cutters, were conducted on sandstone specimens based on an improved uniaxial testing. Afterwards, morphological measurement was performed to analyze the change of the groove volume, using a surface profilometer. Based on the evaluations of typical chips and cracks propagation, the fragmentation modes of the rock between two cutters under different penetration depths were proposed. In addition, the TBM rock breaking efficiency was studied. As the increase of the penetration depth, when the cutter spacing was constant, the results show that: (1) The rock fragmentation modes gradually changed from shear failure and shear-tensile failure to tensile failure. (2) Though penetration energy gradually increased, the groove volumes also increased, thus, the TBM rock breaking efficiency rises. (3) Specific energy decreased first and then gradually increased. It indicates that the optimum penetration depth was existent for different preset penetration depths. With the increase in cutter spacing, the optimum penetration depth also rised. According to the derivation and verification of the analytical formula, the internal relationship between the penetration depth and the fracture toughness was obtained, which was in line with the linear relationship between penetration depth and penetration energy. From a microscopic point of view, the sharp increase of penetration energy with increase of penetration depth can be explained.
Highlights
Tunnel Boring Machines (TBMs) are characterized by less noise, less vibration, a high-degree mechanization and automation, high safety and high reliability
According to the derivation and verification of the analytical formula, the internal relationship between the penetration depth and the fracture toughness was obtained, which was in line with the linear relationship between penetration depth and penetration energy
In order to study the optimum penetration depth and rock breaking characteristics of TBM rock breaking under different cutter spacing, this paper conducted TBM cutter indentation tests under different preset penetration depth and obtained the following conclusions: 1) By observing the changes of the volume and shape of the chips, it was found that the chips gradually develop to interior of rock sample with penetration depth increasing and as the indentation depth increases, the rock failure mode gradually is changed from shear failure and shear-tensile failure to tensile failure
Summary
Tunnel Boring Machines (TBMs) are characterized by less noise, less vibration, a high-degree mechanization and automation, high safety and high reliability. The previous study found that the cutter spacing, and the penetration depth are two important factors, affecting the TBM rock breaking efficiency [1]. They found that the optimum cutter spacing, deriving from numerical simulation, was in good agreement with the linear cutting method (LCM) test results. The existing researches on cutter spacing and penetration depth for TBM rock breaking are mostly based on numerical simulation and research on the effect of TBM single-edge cutter rock breaking. In the practical TBM excavation, instead of single cutter, the group of cutters on the cutter plate can be cooperated to the rock breaking For this reason, the authors of this paper conducted a series of preset penetration depth with cutter spacing tests by a improved uniaxial test equipment, which was designed by the authors. The optimum penetration depth on TBM rock breaking is studied
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