Practical Skills for Rotary Drilling Rigs: Strictly Control Hole Formation Quality and Prevent Hole Collapse and Deviation

    The quality of boreholes created by rotary drilling rigs directly determines the bearing capacity and stability of pile foundation projects. Collapse and deviation are the most common quality risks in practice, which not only affect construction efficiency but may also lead to equipment wear and increased costs. Mastering scientific operational techniques and precisely controlling each construction phase are key to improving borehole quality and avoiding collapse and deviation risks. Based on practical experience, the following core techniques are summarized.

    Thorough pre-construction preparation lays the foundation for drilling. Before actual operations, it is essential to comprehensively review the geological survey report to clarify parameters such as soil layer distribution, moisture content, and looseness, and select appropriate drill bits and construction techniques accordingly—short spiral drill bits are preferred for soft and sandy layers, while core drill bits are used for rock layers to prevent wall disturbances caused by unsuitable drill bits. Additionally, inspect the drilling rig equipment, focusing on adjusting the verticality of the drill rod and the stability of the hydraulic system to ensure the drill rod is straight and joints are secure. Level the working area and compact the foundation to prevent tilting during drilling operations, minimizing the risk of deviation from the outset. Furthermore, prepare qualified wall-protecting slurry in advance, adjusting its viscosity and specific gravity based on soil layer characteristics to ensure effective mud cake formation and prevent borehole wall collapse.

    Precise drilling control and strict hole formation accuracy. During drilling, adhere to the principles of "slow start, steady drilling, and frequent observation." Gradually increase the speed when starting the drill to avoid disturbing the hole wall by impacting it with the drill rod. The drilling speed must match the soil layer characteristics—soft and sandy layers require slower speeds rather than faster ones. Pause for a moment after every 1-2 meters of drilling, allowing the slurry to fully stabilize the hole wall before continuing to prevent collapse due to excessive speed. When drilling through rock layers, speed can be increased appropriately, but rotational speed must be controlled to avoid misalignment caused by drill rod oscillation. Continuously monitor the verticality of the drill rod, using levels and inclinometers for real-time checks. Adjust the drill position immediately upon detecting any tilt, and strictly prohibit forced drilling to ensure the hole formation meets verticality standards.

    Scientific management of drilling mud is essential to prevent hole collapse risks. Drilling mud serves as the core for wall protection and collapse prevention. In practice, real-time monitoring of mud indicators is required. If the mud viscosity is insufficient or the specific gravity is too low, additives should be promptly added to adjust, avoiding rapid mud loss and unstable hole walls. If the mud sand content is excessively high, timely purification treatment is necessary to prevent sand particle deposition at the hole bottom, which could affect the quality of hole formation. During drilling, maintain the mud level higher than the groundwater level or the hole opening by a certain height; in deep water or areas with abundant groundwater, increase the mud circulation volume to enhance wall protection. After hole formation, immediate cleaning is required using a reasonable cleaning process to thoroughly remove bottom sediment. Concrete should be poured immediately after cleaning to avoid prolonged exposure of the hole wall leading to collapse.

    Standardized handling of anomalies is crucial to avoid quality hazards. In practice, if minor hole collapse occurs, drilling should be stopped immediately, the mud specific gravity increased, and the circulation speed slowed down. Resume slow drilling only after the hole wall stabilizes. If severe collapse occurs, the hole should be promptly backfilled with clay or gravel, and re-drilled, strictly prohibiting blind continuation of construction. When deviation is detected, if the deviation is slight, adjust the drill rig position and ream slowly to correct it. If the deviation is significant, backfill above the deviated position and re-drill to correct the deviation, preventing excessive deviation from affecting pile foundation bearing capacity. Additionally, regularly inspect the wear of drill rods and bits, and replace worn parts promptly to prevent equipment failures from causing hole quality issues.

    Conclusion: The core of practical operation of rotary drilling rigs is 'precision, stability, and compliance'. By ensuring adequate pre-operation preparation, scientific drilling control, strict mud management, and standardized anomaly handling, both effective improvement of hole quality and maximum reduction of collapse and deviation risks can be achieved. Operators need to master construction techniques for various soil layers proficiently, flexibly adjust operating parameters, and optimize processes based on on-site conditions to ensure pile foundation hole quality meets standards, laying a solid foundation for subsequent engineering construction.