Selection Guide for Different Geological Rotary Drills: Suitable Schemes for Clay, Sandy Soil, Gravel, and Hard Rock

    The core of rotary drilling rig selection lies in matching geological characteristics. The differences in soil hardness, permeability, and wear resistance among the four types of geology—clay, sand, cobble, and hard rock—significantly determine the selection of rig power, torque, and drill bit type. Scientific selection can enhance construction efficiency, reduce equipment wear, and mitigate risks such as borehole collapse and bit sticking. Based on practical engineering experience, this guide clarifies key considerations for rotary drilling rigs in various geological conditions, offering concise and practical insights tailored to on-site construction needs.

    Clay Geology Adaptation Plan: Clay geology features moderate moisture content and strong plasticity, but it tends to adhere to drill bits, reducing excavation efficiency. The core selection principle is to "balance efficiency with borehole stability." Prioritize medium-torque rotary drilling rigs, with power not necessarily excessive—adequate for clay drilling. Pair drill bits with spiral or bucket-type bits: spiral bits facilitate soil removal, while bucket-type bits minimize clay adhesion. During drilling, optimize bit rotation speed appropriately to prevent clay clumping and clogging, ensuring smooth hole formation.

    Sandy Soil Geological Adaptation Plan: Given the loose and highly permeable nature of sandy soil, which is prone to borehole collapse risks, the core selection principle is "collapse prevention as the primary focus, with efficiency as a secondary concern." Priority should be given to rotary drilling rigs with high torque and excellent anti-collapse performance, ensuring strong machine stability to mitigate construction risks caused by sandy soil disturbance. The drill bit should be a short spiral bit, as the compact spiral design facilitates rapid sand removal. Coupled with high-quality slurry for borehole wall protection, this reduces sand layer collapse and prevents borehole wall instability due to delayed sand removal. Drilling speed must be slowed down to balance sand removal and borehole wall protection effects.

    Gravel Geological Adaptation Plan: Gravel has high hardness and strong wear resistance, with uneven particle sizes that can easily impact drill bits and wear drill rods. The core selection criteria are "high strength and wear resistance." Use a rotary drilling rig with high torque and high-strength drill rods, ensuring sufficient power to break medium-sized gravel particles. Pair the drill bit with a rock bucket or modular drill bit, and select wear-resistant tooth profiles to enhance the drill bit's impact and wear resistance. For larger gravel particles, auxiliary impactors can be used to improve crushing efficiency and reduce equipment wear.

    Hard Rock Geological Adaptation Solution: Hard rock formations are characterized by high hardness and strong integrity, resulting in significant drilling difficulties and severe equipment wear. The core selection principle is "high power and strong fragmentation." Prioritize the use of high-power, high-torque fully hydraulic rotary drilling rigs, which provide ample power to meet the torque requirements for hard rock drilling. Pair the drill bits with core drill bits or roller bits—core drill bits facilitate the fragmentation of hard rock and core extraction, while roller bits enhance drilling efficiency in hard rock. When necessary, supplementary rock drilling equipment can be employed for pre-treatment of hard rock to overcome drilling challenges, ensuring smooth construction progress. Additionally, regularly inspect drill bit wear and promptly replace worn components.

    Conclusion: The selection of rotary drilling rigs must strictly align with actual geological conditions. Blindly pursuing high power and advanced configurations is inadvisable. Parameters and drill bit types should be chosen based on the core characteristics of clay, sand, gravel, and hard rock. In practice, on-site geological survey details can be integrated to flexibly adjust the selection plan, balancing construction efficiency, equipment wear, and safety to ensure the smooth progress of pile foundation projects.