Abstract: Horizontal directional drilling model test apparatus can provide a feasible test platform for exploring the quantitative relationship between drilling and rock physicomechanical parameters. In this research, a model test device that can investigate the correlation between horizontal directional drilling parameters and rock strength is independently developed to observe the application of horizontal directional drilling technology in tunnel geological investigations. The device includes drilling pressure power, rotary power, and parameter measurement systems. The drilling pressure power and rotation power systems are driven by positive displacement motors and hydraulic cylinders, respectively, which can measure displacement, drilling pressure, rotational speed, torque, system water pressure, and water flow rate. The feasibility of the test system is tested using six mortar test blocks with a strength grade of M15, and the following results are obtained. (1) The drilling speed of horizontal directional drilling and the reaction torque of the bit increase with increasing drilling pressure. (2) A positive proportional change relationship exists between the mud system circulation pressure and the reaction torque of the bit, as well as between the mud system circulation flow and the rotational speed of the bit. (3) The quantitative relationship between drilling parameters and rock strength can be studied using the test device while preserving the working characteristics of horizontal directional drilling.

Key words: horizontal directional drilling, model test device; drilling parameters, tunnel exploration