Effect of Hole Length on Long-Hole Drilling Performance
In this study, systematic in-situ tests along Suzuka tunnel were carried out to examine the drilling performance in case of drilling holes up to 50 m depth. Special care was taken to clarify the effect of hole length on drilling performance such as penetration rate, rotational torque and oil pressure applied to the rock drill.
Results can be summarized as follows;
1) Averaged penetration rate has a declining trend with increase of hole length. Energy of elastic wave is gradually decreasing while propagating rods. Averaged decrease of penetration rate was 1.5 % per 3 m-length rod.
2) Averaged penetration rate fluctuated especially at 20 m and 40 m of hole length. It was considered that an interaction between piston movement and reflected wave from the bit caused this considerable amount of fluctuation.
3) Rotational torque has an increasing trend with increase in hole length and frictional resistance between drill rod and hole.
Key Words: Drilling, Rock Drill, Penetration Rate, Tunnel, Sleeve, reflected wave