The performance prediction of impact hammers from Schmidt hammer rebound values in Istanbul metro tunnel drivages

“…These models are mostly determined empirically in specific mine sites and are valid for a limited range of rock and rock mass properties, whereas some of the models incorporate some idea about the rock mass (e.g. by taking the RQD into account) and others focus on the rock strength and some also on abrasivity and hardness of the rock Bilgin et al (1996Bilgin et al ( , 1997Bilgin et al ( , 2002 developed a model for axial-type roadheaders. Based on the rock mass cuttability index (RMCI), they calculate the net cutting rate (NCR) according to the following formulas: and A similar model for radial-type roadheaders is proposed by (Copur et al 1998).…”

Section: Performance Prediction Of Roadheadersmentioning

confidence: 99%

Theoretical Investigations on the Influence of Artificially Altered Rock Mass Properties on Mechanical Excavation

Hartlieb

Bock

2017

Rock Mech Rock Eng

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guaranteeing the access to mineral deposits and for extracting the valuable minerals from these deposits. Mechanical excavation tools like full-face tunnel boring machines and roadheaders use either discs or conical picks for applying the required forces into the rock mass. The efficiency of the processes is mainly governed by the mechanical properties of the rock type, especially strength and abrasivity. Roadheaders are limited by a uniaxial compressive strength of 150 MPa, TBMs by roughly 300 MPa. In particular, the development of underground mines furthermore requires a high flexibility of the used equipment which is mainly characterised by the turning radius of the machine. The rather simple relationship is the harder the rock, the bigger the machine, the lower the flexibility.In order to improve the performance of their machines, most machine manufacturers on the market have introduced new machine concepts recently. Many of which change the cutting principle and apply the so-called undercutting technology (e.g. Aker Wirth "Mobile Tunnel Miner", Atlas Copco "Mobile Miner", Joy Mining "Oscillating Disc Cutter", Caterpillar "Rock Straight system" and Sandvik "MX650" (Sifferlinger et al. 2017)).In addition to changing the machine concept, the goal of extended research activities all over the world during the last decade is focussed on overcoming the highlighted restrictions. The major focus is set on artificially altering the rock mass properties in order to ease the machines' life by reducing the UCS and rock mass rating. This can be done by introducing cracks and/or slots in the rock mass which help the subsequent cutting process with a conical tool. The technologies under consideration are high-power lasers Parker et al. 2003;Graves and Bailo 2005), microwaves (Toifl et al. 2017; Hartlieb and Grafe 2017), high-pressure water jets (Ciccu and Grosso 2010;Miller 2016) and activated tools (Keller and DrebenstedtAbstract This study presents a theoretical analysis of the influence of the rock mass rating on the cutting performance of roadheaders. Existing performance prediction models are assessed for their suitability for forecasting the influence of pre-damaging the rock mass with alternative methods like lasers or microwaves, prior to the mechanical excavation process. Finally, the RMCR model was chosen because it is the only reported model incorporating a range of rock mass properties into its calculations. The results show that even very tough rocks could be mechanically excavated if the occurrence, orientation and condition of joints are favourable for the cutting process. The calculated improvements in the cutting rate (m 3 /h) are up to 350% for the most favourable cases. In case of microwave irradiation of hard rocks with an UCS of 200 MPa, a reasonable improvement in the performance by 120% can be achieved with as little as an extra 0.7 kWh/m 3 (= 1% more energy) compared to cutting only.

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“…Schmidt hammer rebound values were found to be a good indicator of rock compressive strength and rock geological discontinuities [11]. Some researchers found strong correlations between the Schmidt hammer value and the cutting rate of roadheaders and tunnel boring machines (TBM), and also mine roof classification [39][40][41][42][43][44][45]. However, the approaches that have been developed for determining optimum test numbers on rock faces were different from each other and inadequate.…”

Section: Tests On Rock Massesmentioning

confidence: 99%