Observations of crack growth in hard rock loaded by an indenter

Cook, N.G.W.; Hood, M.; Tsai, Feng Chun

doi:10.1016/0148-9062(84)91177-x

Cited by 139 publications

(53 citation statements)

References 4 publications

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“…The length of the cracks is a function of the pressure in the crushed zone, which in turn is a function of the cutter normal force. The cut interaction depends on spacing between the cuts, the angle, and extension of cracks between the adjacent cuts [6].…”

Section: Background Of the Studymentioning

confidence: 99%

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Optimization of Tunnel Boring Machine (TBM) Disc Cutter Spacing in Jointed Hard Rock Using a Distinct Element Numerical Simulation

Naghadehi

Mikaeil

2016

Period. Polytech. Civil Eng.

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The Tunnel Boring Machine (TBM) IntroductionRock cutting with a Tunnel Boring Machine (TBM) involves the indentation of a rock surface by cutting tools, which are mounted in an array on the front of a cutterhead. A simplistic view of a TBM would be that of a machine which generates thrust to push the cutterhead forward and supplies torque to turn the cutterhead against the tangential forces resisting the cutting tool motion and indentation [1]. During the excavation, TBM disc cutters roll across the tunnel face and continuously expand the crushed zone immediately beneath them. Then, cracks are initiated from the crushed zone and propagated downwards and sideward. One or more cracks under the action of the rolling cutter may reach the free surface or propagate to meet the cracks of the neighboring cuts. In these two cases, chipping occurs [2]. This interaction and subsequent fragmentation process are directly relevant to the design of the TBM cutterhead and the efficiency of TBM excavation. The line spacing of adjacent cutters is the main parameter governing the interaction mechanism. In addition, the presence of joints and discontinuities in rock will make the interaction more complex.This research studies the fragmentation of rock under the effect of two neighboring cutters in different joint frequencies. Most of the main former researches on various cases related to TBM disc cutters fragmentation process have been done with consideration of homogeneous and isotropic rocks. Among these investigations, those that were concerned with cutter spacing optimization and related issues are explained below.Roxborough [3] deduced an equation for the cutter spacing, in terms of the assumption of rock shear failure between two adjacent cuts. The ratio of cutter spacing to penetration is equal to the ratio of the uniaxial compressive strength to the shear strength. By utilizing the linear rock cutting rig, Snowdon et al. [4,5] performed a series of linear cutting tests. The effects of the penetration and the ratio of cutter spacing to penetration on specific energy were analyzed. The correlation between cutter spacing and the three forces acting on the cutters was also studied. The optimum value of the ratio of cutter spacing to penetration for granite, dolerite and sandstone was found to be about 10 and that for limestone was approximately 15. The

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Section: Background Of the Studymentioning

confidence: 99%

“…The optimum penetration was about 10 mm for granite, dolerite and sandstone. Cook et al [6] examined the effects of indenter size and confining stress on the rock indentation test and compared it with numerical simulation based on the Finite Element Method (FEM).…”

Section: Introductionmentioning

confidence: 99%

Optimization of Tunnel Boring Machine (TBM) Disc Cutter Spacing in Jointed Hard Rock Using a Distinct Element Numerical Simulation

Naghadehi

Mikaeil

2016

Period. Polytech. Civil Eng.

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“…The results demonstrated that a small increase of confining pressure caused the position of the maximum tensile stress to move significantly from the vertical thrust line and increased the crack vertical angle. Cook et al [23], Liu et al [24], and Ma et al [25] reported that cracks tend to develop to the free surface once the confining pressure increases. It is worth mentioning that field investigations, laboratory tests, and numerical simulations can promote perceiving the mechanism of rock breaking of TBM in the presence of various confining pressures.…”

Section: Introductionmentioning

confidence: 99%

“…It is worth mentioning that field investigations, laboratory tests, and numerical simulations can promote perceiving the mechanism of rock breaking of TBM in the presence of various confining pressures. However, most previous studies were undertaken as two-dimensional (2D) [23][24][25], imposing barriers to truly representing the breaking mechanism in three-dimensional (3D) spaces.…”

Section: Introductionmentioning

confidence: 99%

Rock Fragmentation Characteristics by TBM Cutting and Efficiency under Bi-Lateral Confinement

Chen

2018

Applied Sciences

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Abstract:In this study, the mechanisms of rock breakage are assessed using tunnel boring machine (TBM) disc cutters under bi-axial pressure. Sequential indentation tests were conducted on granite specimens using a tri-axial testing platform. The morphology and volume of the fractured surface were measured and analyzed using a three-dimensional surface profilometer. An analysis of rock breaking growth and efficiency was performed as well. When the minor confining pressure (σ 1 ) is constant, the results show that a larger difference in confining pressure leads to a larger volume of fractured surface, thereafter improving the rock-breaking efficiency even though the penetration energy is enlarged. On the other hand, when the major confining pressure (σ 2 ) is constant, the penetration energy increases proportionally with the σ 1 ; however, the volume of fractured surface is decreased, and the breaking efficiency is attenuated as well.

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“…Roxborough and Phillips [5,6] presented the concept of groove-deepening in rock cutting process. In the past decades many other empirical researches have also been carried out to investigate the mechanism of rock fragmentation by Ozdemir and Miller [7], Wang and Ozdemir [8], Lindqvist [9], Cook et al [10], Lindqvist et al [11], Kou [12], and Liu [13] respectively. A numerical model has been presented by Kou et al [14] to study the rock fragmentation under the action of a drill bit in terms of rock heterogeneity.…”

Section: Introductionmentioning

confidence: 99%

The comparative analysis of rocks’ resistance to forward-slanting disc cutters and traditionally installed disc cutters

2015

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At present, disc cutters of a full face rock tunnel boring machine are mostly mounted in the traditional way. Practical use in engineering projects reveals that this installation method not only heavily affects the operation life of disc cutters, but also increases the energy consumption of a full face rock tunnel boring machine. To straighten out this issue, therefore, a rock-breaking model is developed for disc cutters' movement after the research on the rock breaking of forward-slanting disc cutters. Equations of its displacement are established based on the analysis of velocity vector of a disc cutter's rock-breaking point. The functional relations then are brought forward between the displacement parameters of a rock-breaking point and its coordinate through the analysis of micro displacement of a rock-breaking point. Thus, the geometric equations of rock deformation are derived for the forward-slanting installation of disc cutters. With a linear relationship remaining between the acting force and its deformation either before or after the leap breaking, the constitutive relation of rock deformation can be expressed in the form of generalized Hooke law, hence the comparative analysis of the variation in the resistance of rock to the disc cutters mounted in the forward-slanting way with that in the traditional way. It is discovered that with the same penetration, strain of the rock in contact with forwardslanting disc cutters is apparently on the decline, in other words, the resistance of rock to disc cutters is reduced. Thus wear of disc cutters resulted from friction is lowered and energy consumption is correspondingly decreased. It will be useful for the development of installation and design theory of disc cutters, and significant for the breakthrough in the design of full face rock tunnel boring machine.

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Observations of crack growth in hard rock loaded by an indenter

Cited by 139 publications

References 4 publications

Optimization of Tunnel Boring Machine (TBM) Disc Cutter Spacing in Jointed Hard Rock Using a Distinct Element Numerical Simulation

Optimization of Tunnel Boring Machine (TBM) Disc Cutter Spacing in Jointed Hard Rock Using a Distinct Element Numerical Simulation

Rock Fragmentation Characteristics by TBM Cutting and Efficiency under Bi-Lateral Confinement

The comparative analysis of rocks’ resistance to forward-slanting disc cutters and traditionally installed disc cutters

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