【正文】 formance prediction models in difficult ground conditions. Hereke tunnel is chosen for this purpose. The first 50 m of the tunnel is horizontal. Later 225 m is inclined with 9_ and excavated is excessive water ingress and clay in some sections. Detailed in situ observations are made during the tunnel excavation and rock samples are collected for testing in the laboratories of the Mining Engineering Department of Istanbul Technical University for ground characterization. antaneous cutting rate of the roadheader used in the project is explained by some geological and geotechnical factors. Factors affecting machine utilization time is also explained in detail. 2. Description of the tunnel project The Hereke Tunnel, located in Turkey in the city of Kocaeli next to Istanbul, was constructed for material transportation between the Nuh Cement Dock and Nuh Cement Plant. Tunneling was the best choice to avoid traffic disruption, since there was a railway, highway and freeway on the surface. The contractor firm STFA Co. was awarded the tunneling project. The tunnel included 50 m of horizontal section (chainage 0–50 m), where excavation started up, and 225 m of 9_ inclined section (chainage 50–275 m). The excavation was performed in a horizontally straight alignment through sedimentary formations including dry (chainage 0–50 and 150–275 m) and wet sections (chainage 50–150). Excavation was performed by using a shielded roadheader, HerrenknechtSM1 with 90 kW of cutter head power, in the excavation diameter of m. Two shafts were sunk in the plant side of the tunnel. The first shaft was planned to be used for cement transportation from the plant to the dock via steel pipe line and the second shaft for coal transportation to the plant via a belt conveyor and skip haulage system. 3. Geology of the project site The Hereke Tunnel passes through a formation of the Upper Cretaceous age. The formation exhibits fractured and folded structure with the direction of 48–52_N and the dip of 30_NE. The strata types encountered in this relatively shallow tunnel (3–21 m of overburden) are nodular marl and thin and thick laminated clayey limestone, carbonated claystone and thin laminated silisified limestone. Some levels of laminated limestone (chainage from 50 to 150 m) form a fractured aquifer causing water ingress in the tunnel. The tunnel is divided into six sections according to their structural and geotechnical differences. Fig. 1 presents the general layout of the tunnel and shafts and the geological crosssection along the tunnel route. The results of geotechnical tests are presented in Table 2. 6. Roadheader performance analysis in different zones Excavation of the Hereke Tunnel was pleted in 2 months with an average daily advance rate of m. During this period, related field data, including machineperformance and geotechnical parameters, were recorded by the authors of this paper. Performance of the roadheader was continuously recorded, including instantaneous cutting rate, machine utilization time and all stoppages for the different zones in the tunnel route. Instantaneous (or ) cutting rate (ICR) is defined as is the production rate for the actual () cutting time of the machine (ton or solid bank m3/cutting hour). Machine utilization time (MUT) is the excavation time as a percentage (%) of the total working time, excluding all the stoppages. Advance rate (AR) is the linear advance rate of the tunnel or drift excavation (m/shift, m/ day, m/week and m/month) and is a function of ICR, MUT and crosssection area of the excavated face. Water ingress and geological discontinuities in the tunnel face were also recorded. The recorded instantaneous cutting rate, water ingress, RQD values of the face and machine utilization time values are tabulated for different tunnel zones in Table 3. Machine utilization, percentages of stoppages and other planned jobs such as ring montage, site surveying, etc. are presented in Fig. 3. 7 .The effect of strata inclination One of the most accepted methods for determining the roadheader cutting rate in horizontal and widely jointed rock formation is to use laboratory cutting specific energy obtained from instrumented core cutting test (McFeatSmith and Fowell, 1979). As seen from Table 2, the samples taken from nodular marl, zone 1, have the specific energy value of 11 MJ/m3, which corresponds to an instantaneous cutting rate of 8 solid bank m3/cutting hour for noninclined strata and medium weight roadheaders in the McFeatSmith and Fowell’s model. However, it is observed in the site that the inclination of the strata is in favor of the cutting action and the muck is easily ing out from the excavated area. The instantaneous cutting rate in this area (zone 1) is recorded to be 10 solid bank m3/cutting hour. . The effect of tunnel inclination In zone 5, having the same pressive strength and specific energy values as in zone 1, the instantaneous cutting rate is more than double being 25 solid bank m3/ cutting hour. The inclination of the tunnel, hence, the gravity forces help the muck being loaded easily and ing quickly on the cut face preventing the muck recirculation within the cutting head and the face. . The effect of rock strength and specific energy values Samples taken from zone 5 have pressive strength of 210 kg/cm2 and specific energy of MJ/m3, and samp