Effects of discontinuities on penetration of TBM cutters

Abstract

Based on the triaxial testing machine and discrete element method, the effects of embedded crack on rock fragmentation are investigated in laboratory tests and a series of numerical investigations are conducted on the effects of discontinuities on cutting characteristics and cutting efficiency. In laboratory tests, five propagation patterns of radial cracks are observed. And in the numerical tests, firstly, it is similar to laboratory tests that cracks ahead of cutters mainly initiate from the crushed zone, and some minor cracks will initiate from joints. The cracks initiating from crushed zones will run through the thinner joints while they will be held back by thick joints. Cracks tend to propagate towards the tips of embedded cracks, and minor cracks will initiate from the tips of embedded cracks, which may result in the decrease of specific area, and disturbing layers play as ‘screens’, which will prevent cracks from developing greatly. The peak penetration forces, the consumed energy in the penetration process and the uniaxial compression strength will decrease with the increase of discontinuities. The existence of discontinuities will result in the decrease of the cutting efficiency when the spacing between cutters is 70 mm. Some modifications should be made to improve the efficiency when the rocks containing groups of discontinuities are encountered.

Keywords

tunnel boring machine (TBM) cutter / triaxial testing machine / numerical model / discontinuity / cutting characteristic / cutting efficiency

References

[1] ZhangZ-hA theory of the rock-breaking mechanism of the TBM and its cutting tool [M], 2003BeijingChina Railway Press3-8

[2] ZhangZ-h, MengL, SunF. Design theory of full face rock tunnel boring machine transition cutter edge angle and its application [J]. Journal of Mechanical Engineering, 2013, 26(3): 541-546

[3] TanQ, YiN-e, XiaY-m, XuZ-j, ZhuY, SongJ-h. Research on rock dynamic fragmentation characteristics by TBM cutters and Cutter spacing optimization [J]. Chinese Journal of Rock Mechanics and Engineering, 2012, 31(12): 2453-2464

[4] MoZ-z, LiH-b, ZhouQ-c, HeE-g, ZouF, ZhuX-m, ZhaoYu. Research on numerical simulation of rock breaking using TBM disc cutters based on UDEC method [J]. Rock and Soil Mechanics, 2012, 33(4): 1196-1202

[5] TanQ, XuZ-j, XiaY-m, ZhangK. Numerical study on mode of breaking rock by TBM cutter in two cutting orders [J]. Journal of Central South University (Science and Technology), 2012, 43(3): 940-946

[6] WangS Y, SloanH S W, LiuY, TangC A. Numerical simulation of the rock fragmentation process induced by two drill bits subjected to static and dynamic (impact) loading [J]. International Journal of Rock Mechanics and Mining Sciences, 2011, 44: 317-332

[7] ZHANG Kui, XIA Yi-min, TAN Qing, ZHOU Zi-long. Numerical study on modes of breaking rock by TBM cutter under different confining pressures [J]. Chinese Journal of Geotechnical Engineering, 2010(11): 1780–1787. (in Chinese)

[8] CookN G, HoodM, TsaiF. Observation of crack growth in hard rock loaded by an indenter [J]. International Journal of Rock Mechanics & Mining Science, 1984, 21(2): 97-107

[9] HuangH, DamjanalB, DetournayE. Normal wedge indentation in rocks with lateral confinement [J]. Rock Mech Rock Eng, 1998, 31(2): 81-94

[10] LiuH Y, KouS Q, LindqvistP A, TangC A. Numerical simulation of the rock fragmentation process induced by indenters [J]. International Journal of Rock Mechanics & Mining Science, 2002, 39: 491-505

[11] MaH-s, YinL-j, JiH-g. Numerical study of the effect of confining stress on rock fragmentation by TBM cutters [J]. International Journal of Rock Mechanics & Mining Science, 2011, 48: 2021-1033

[12] MA Hong-su, JI Hong-guang. Experimental study of the effect of joint orientation on fragmentation modes and penetration rate under TBM disc cutters [J]. Chinese Journal of Rock Mechanics and Engineering, 2011(1): 155–163. (in Chinese)

[13] GongQ M, JianZ, JiaoY-y. Numerical modeling of the effects of joint orientation on rock fragmentation by TBM cutters [J]. Tunneling and Underground Space technology, 2005, 20: 183-191

[14] YoonJ. Application of experimental design and optimization to PFC model calibration in uniaxial compression simulation [J]. International Journal of Rock Mechanics and Mining Science, 2007, 44: 871-889

[15] GongQ M, JiaoY Y, ZhaoJ. Numerical modeling of the effects of joint spacing on rock fragmentation by TBM cutter [J]. Tunneling and Underground Space Technology, 2006, 21: 46-55

[16] EftekhariM, BaghbananA, BagherpourR. The effect of fracture patterns on penetration rate of TBM in fractured rock mass using probabilistic numerical approach [J]. Arabian Journal of Geoscience, 2014, 7(12): 5321-5331

[17] BejariH, HamidiJ K. Simultaneous effects of joint spacing and orientation on TBM cutting efficiency in jointed rock masses [J]. Rock Mechanics and Rock Engineering, 2013, 46: 897-907