Introduction
Rotary drilling rigs are essential construction machinery designed for hole-forming operations in various engineering projects. Widely used in municipal construction, highway bridges, high-rise buildings, and other foundation works, these rigs can adapt to different drilling conditions, including dry (short auger), wet (rotary bucket), and rock formations (core drilling). With high installed power, substantial output torque, significant axial pressure, flexibility, and multifunctionality, rotary drilling rigs offer exceptional efficiency.
These rigs are suitable for most soil and geological conditions across China, making them ideal for bridge construction, high-rise building foundations, and other engineering applications. Today, rotary drilling rigs are extensively utilized in bored pile projects. Therefore, a technical discussion on construction preparation and common water-based construction techniques is highly significant.
1. Construction Preparation
1.1 Data Preparation
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Geological & Hydrological Data: Obtain site-specific engineering and hydrogeological data before commencement, along with pile foundation construction drawings and review records.
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Site Survey: Investigate underground pipelines (pipes, cables), structures, hazardous buildings, and sensitive facilities in and around the construction area.
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Material & Equipment Testing: Conduct physical property tests on required materials and prepare concrete mix ratios through qualified laboratories.
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Construction Plan: Develop an effective construction organization plan or method statement, including load and process references.
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Safety & Quality Briefing: Review drawings, conduct detailed safety and technical briefings, and encourage worker participation in planning discussions to enhance safety and quality awareness.
1.2 Machinery & Equipment
Ensure all measuring instruments (total station, theodolite, level, steel tape) and machinery (rotary drilling rig, welding machine) have valid factory certifications.
1.3 Small & Medium-Sized Tools Requirements
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Mixer: Must be firmly installed with a rainproof canopy; clutches, brakes, wire ropes, and guards must be safe and functional. Operators must be certified, and proper grounding is required.
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Handheld Power Tools: Equipped with independent leakage protectors, intact guards, and proper grounding. Avoid damaged cables.
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Welding Machine: Must have rainproofing, grounding protection, and insulated wiring. Welders must be certified.
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Gas Cylinders: Clearly labeled with anti-vibration rings; maintain >5m distance between oxygen and acetylene cylinders. Use flashback arrestors and secure hoses. Operators must be certified.
1.4 Installing Drilling Tools
Drilling tools must be rigid to prevent movement during operation. Installation should comply with the manufacturer’s standards. Various drill bits (short auger, rotary bucket, core drill) are selected based on soil conditions:
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Short Auger: Suitable for cohesive soil, silt, fill, medium-density sand, and weathered rock above the water table.
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Rotary Bucket: Used with slurry support for cohesive soil, silt, sand, fill, gravel, and weathered rock.
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Core Drill Bit: Ideal for gravel, moderately hard rock, and weathered formations.
2. Common Water-Based Construction Technique
2.1 Drilling Process
Rotary drilling involves a bucket with a bottom valve that breaks and collects soil, which is then lifted and unloaded cyclically until reaching the desired depth.
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Stable Formations: Dry or water-based drilling (no slurry needed).
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Unstable Formations: Use slurry support to prevent collapse.
2.2 Site Layout
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Level and compact the site, remove debris, and mark pile positions with cross-reference stakes.
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Keep access routes away from drilling to avoid destabilizing boreholes.
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For shallow water, build an island 1.0m above water level for rig placement.
2.3 Pile Positioning
Follow the “whole-to-part” principle for accurate positioning, verified using a total station.
2.4 Rig Positioning
Ensure the rig is in good condition and properly aligned before drilling.
2.5 Steel Casing Installation
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Land Construction: Use the pit method for casing placement, ensuring verticality and watertightness.
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Underwater Construction: Embed casing into stable soil ≥0.5m deep.
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Specifications:
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4mm–6mm thick for ≤4m casings; 6mm–8mm for longer casings.
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Weld multi-section casings for rigidity and leak prevention.
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Inner diameter > drill bit size.
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Top elevation 1.5m–2.0m above water level and 0.3m above ground.
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2.6 Drilling Operations
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Water-Based Drilling: Monitor depth via the rig’s display, adjusting for real-time progress.
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Unstable Formations: Inject slurry for wall support.
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Procedure:
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Lower the drill bit, reset the depth gauge, and begin rotation.
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Extract and unload soil periodically, recording geological samples.
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Maintain verticality via automated or manual adjustments.
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2.7 Geological Recording
Document drilling speed, depth, and soil samples, comparing findings with design specifications. Report discrepancies to supervisors.
2.8 Hole Inspection
After reaching design depth, check hole diameter, verticality, and sediment thickness. Use a hammer to compact loose soil in dry holes or slurry cleaning for wet holes.
2.9 Hole Cleaning
Critical for pile quality:
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Primary Cleaning: Circulate fresh slurry for ≥ 30 min until sediment <4%.
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Secondary Cleaning: Perform after installing rebar cages to ensure minimal sediment before concreting.
Conclusion
Rotary drilling rigs are indispensable in modern construction, offering versatility and efficiency across diverse geological conditions. Proper preparation, precise execution, and adherence to water-based techniques ensure high-quality outcomes in bored pile projects. By following standardized procedures and leveraging advanced monitoring, engineers can optimize performance and durability in foundation works.
