Experimental Study on the Correlation Between Horizontal Directional Drilling Parameters and Rock Strength

Exploring the quantitative relationship between drilling parameters and rock strength offers valuable data for enhancing rock engineering safety. This study employed a self-designed horizontal directional drilling (HDD) experimental apparatus, using a controlled variable method to examine the effects of thrust force and rock strength on HDD drilling efficiency. The relationship between the total energy consumption of a tricone bit and rock strength was analyzed from an energy perspective. Introducing the concept of mechanical specific energy (MSE), the study established a quantitative relationship between MSE and uniaxial compressive strength (UCS) through data fitting. Key findings include: In tests on six M15-grade mortar specimens, increasing thrust force led to proportional increases in drilling speed and reaction torque. Fluid flow rate correlated positively with rotational speed, while fluid pressure correlated positively with reaction torque, aligning with the positive displacement motor (PDM) operating principles. In tests involving mortar and rock specimens of varying strengths, drilling speed negatively correlated with thrust force as specimen strength increased. At the same time, reaction torque positively correlated with thrust force. The total energy consumption of the tricone bit increased linearly with drilling depth, with higher-strength rock specimens exhibiting steeper slopes, indicating greater energy demand. Data fitting between MSE and UCS produced a correlation coefficient of R2 = 0.91932, demonstrating a strong linear relationship. These findings provide a reliable theoretical reference for applying HDD in tunnel geological investigations and can guide the optimization of drilling parameters for improved construction efficiency and safety.