Some geological and geotechnical factors affecting the performance of a roadheader in an inclined tunnel

The factors affecting the performance of 90 kW-shielded roadheader is investigated in detail in a tunnel excavated for Nuh Cement Factory. The first part of the tunnel is horizontal and the second part is inclined with 9° and excavated uphill. Tunnel passes through a formation of the Upper Cretaceous age with nodular marl, carbonated claystone, thin and thick laminated limestone. Water ingress changes from 0 to 11 l/min. In six different zones it is found that the rock compressive strength changed from 20 to 45 MPa, tensile strength from 1 to 4 MPa, specific energy from 11 to 16 MJ/m³, plastic limit from 15% to 29%, liquid limit from 27% to 43% and water absorption from 4% to 18% in volume. Detailed in situ observations show that in dry zones for the same rock strength the inclination of the tunnel and the strata help to increase the instantaneous cutting rate from 10 to 25 solid bank m³/cutting hour. The effect of water on cutting rate is dramatic. In the zones where the plastic limit and the amount of Al₂O₃ is low, instantaneous cutting rate increases from 34 to 50 solid bank m³/cutting hour with increasing water content from 3.5 to 11 l/min. However, in the strata having high water absorption characteristic and high amount of Al₂O₃, cutting rate decreases considerably due to the sticky mud, causing problem to the cutterhead. Excavation, muck loading and support works are performed separately due to safety concerns in the wet and inclined sections which reduced the machine utilization time from 38% to 8%. The information gathered is believed to form a sound basis in contributing the performance prediction of roadheaders in difficult ground conditions.