Researchers have consistently made endeavors to suggest more accurate performance prediction models for mechanical excavators. Apart from machine related parameters, physical and mechanical properties of rocks have an impact on excavation performance. In this research, using the data collected from Levent- Hisarüstü metro tunnel (Istanbul), an attempt was made to find the rock properties that are more closely related to performance of impact hammers. The tunnel was divided into 60 zones. For each zone, the instantaneous breaking rate (IBR) of the hammer used to excavate the tunnel was recorded. The rock quality designation (RQD), uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), density (ρ), Schmidt hammer hardness (SHH), Shore Scleroscope hardness (SSH), and Cerchar abrasivity index (CAI) were realized for each zone. Next, the correlations between each possible pair of the rock properties were investigated. The results were tested for significance at 0.99 and 0.95 confidence intervals.
Mechanical excavation can serve as a fast method which can also provide more control on strata and more security in working environment (Robbins 2000). To choose the best method of excavation, one should consider feasibility, installation problems, ability of negotiation with adverse geological conditions, total cost and advance rate (Terezopoulos 1987). Therefore, determining the advance rate (performance) of an excavator is a must even from the very early phase of feasibility studies (Aksoy et al. 2013).
Parallel with the properties of the machine itself, physical and mechanical properties of the rock mass and the intact rock affect the performance of mechanical excavators. Past researches have shown that the power of the machine can sufficiently represent the effect of the machine properties on performance of mechanical excavators. They have also shown that the performance of the mechanical excavators is linearly proportional to their power (Copur et al. 2001, Copur et al. 2011, Balci et al. 2004, Rostami et al. 1994). However, the researchers have not concluded such an agreement on the rock properties affecting the performance of the hammers (Bilgin et al. 2002, Bilgin et al. 1997, Aksoy 2009, Aksoy 2013, Aksoy et al. 2011, Aksoy et al. 2013). Thus, the present study aimed to find the rock properties that have a major effect on the performance of the hammers. In order to reach that purpose, the Levent-Hisarüstü metro tunnel was carefully investigated. The tunnel is located in the European side of Istanbul and is constructed using the new Austrian tunneling method (NATM). An MTB 120 impact hammer mounted on a JCB excavator was used to excavate this tunnel. Field and laboratory studies were carried out to measure the instantaneous breaking rate (IBR) of the hammer as well as the properties of the rock mass and the intact rock that were associated with each sample.
