The performance of a roadheader in high strength rock formations in Küçüksu tunnel

The main objective of this study was to investigate the performance of a roadheader used for the excavation of Küçüksu Sewage Tunnel having a length of 1037.52 m. The tunnel is located in Anatolian part of Istanbul and constructed by STFA for Istanbul Water and Sewerage Administration (ISKI). Detailed statistical analysis showed that net advance rate of the roadheader is directly influenced by rock compressive strength, rock mass quality designation and water income. In the second stage of the research study, a big rock block taken from the tunnel face was subjected to fullscale rock cutting tests in the laboratory using a linear cutting machine. Cutter force and specific energy values were recorded for different depths of cut and cutter spacings and likely net cutting rate of the roadheader excavating rock formation was predicted using specific energy and cutter head power. In situ cutting rate and laboratory predicted values were compared in order to test the validity of the full scale rock cutting tests. Figure 1. The route of Küçüksu tunnel. lining was used as secondary tunnel support and PVC lining to protect concrete from harmful effect of the sewage water. 3 TUNNEL GEOLOGY AND SOME ROCK PROPERTIES Rock samples were collected systematically and geological observations were made during tunnel excavations. The main rock formation is limestone (72%) having compressive strength values changing from 600 to 1452 kg/cm2 and RQD values from 40% to 90%. 16% of the rock formations are andesite and diabase dykes with compressive strength from 741 to 1638 kg/cm2 and RQD 80–90%. Petrographic descriptions of the samples collected from different tunnel chainages are given in Table 1. A geological cross section of the tunnel with RQD and water income values in different rock strata is given in Figure 4. 4 PERFORMANCE PREDICTION OF THE ROADHEADER IN KÜÇÜKSU TUNNEL In recent years the application of roadheaders in hard rock formations has increased considerably. However the prediction of the net cutting rate and machine utilization time determining daily advance rates still stays a key factor in determining the economy of tunnel excavation. Although in the past many roadheader performance prediction models were published (McFeat-Smith, Fowell 1977–79; Bilgin et al. 1990–1996–1997; Thuro, Plinninger 1998–1999; Çopur 1997–1998), one of the most realistic method to predict the cutting rate of any excavation machine in massive rock formations was reported to use cutting power, optimum specific energy and energy transfer ratio as given in Equation 1 (Rostami, Ozdemir 1994).