Introduction
Rotary drilling rigs are construction machinery designed for hole-forming operations in foundation engineering. They are widely used in municipal construction, highway bridges, high-rise buildings, and other foundation projects. Equipped with different drilling tools, they adapt to dry (short auger), wet (rotary bucket), and rock layer (core drill) hole-forming operations. Rotary drilling rigs feature high installed power, large output torque, significant axial pressure, flexibility, high construction efficiency, and multifunctionality.
These rigs are suitable for soil and geological conditions in most regions of China, making them versatile for bridge construction, high-rise building foundations, and other engineering applications. Currently, rotary drilling rigs are widely used in various bored pile projects. Therefore, a technical discussion on construction preparation and common water-based construction techniques is essential.
1. Construction Preparation
1.1 Data Preparation
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Geological & Hydrological Data: Obtain site engineering geological and necessary hydrological data before construction, along with pile foundation construction drawings and review records.
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Underground Survey: Investigate underground pipelines (pipes, cables), structures, hazardous buildings, and precision instrument workshops in and near the site.
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Equipment & Material Testing: Collect technical performance data for the main construction machinery and supporting equipment. Conduct physical property tests on materials and prepare concrete mix ratios through qualified laboratories.
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Construction Plan: Ensure an effective construction organization design or work plan, including load and process test references.
1.2 Drawing Review & Safety Briefing
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Conduct detailed safety and technical briefings before construction.
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Encourage worker participation in discussing construction plans to enhance safety and quality awareness.
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Evaluate departments for compliance.
2. Construction Machinery & Equipment
Required measuring instruments and machinery (e.g., theodolites, levels, steel tape measures, rotary drilling rigs, welding machines) must have valid factory certifications.
3. Requirements for Small & Medium-Sized Tools
3.1 Mixers
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Must be installed stably with rainproof sheds.
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Clutches, brakes, wire ropes, and guards must be safe and effective.
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Operators must be certified, and proper grounding is required.
3.2 Handheld Power Tools
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Equipped with independent leakage protectors.
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Guards must be intact, and grounding/zeroing is mandatory.
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Avoid damaged rubber cables.
3.3 Welding Machines
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Reliable rain protection and grounding/zeroing.
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Primary and secondary wiring must have protective covers.
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Use proper terminals; avoid messy wiring.
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Welders must be certified.
3.4 Gas Cylinders
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Marked with anti-vibration rings; avoid direct sunlight.
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Maintain >5m between oxygen and acetylene cylinders.
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Acetylene cylinders must have flashback arrestors.
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Secure hoses with clamps; operators must be certified.
4. Installing Drilling Tools
Drilling tools must have sufficient rigidity to prevent movement during operation. Installation should comply with the manufacturer’s standards. Common drill bits include:
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Short Auger: For cohesive soil, silt, fill, dense sand, and weathered rock above the water table.
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Rotary Bucket: For slurry-supported holes in cohesive soil, silt, sand, gravel, and weathered rock.
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Core Auger: For gravel and moderately hard rock.
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Core Drill Bit: For weathered rock and fractured formations.
Select drill bits based on soil conditions.
5. Common Water-Based Construction Techniques
5.1 Rotary Drilling Process
The rig breaks soil/rock with a bucket drill bit, lifts it to the surface, and repeats the process. For stable formations, dry or water-based drilling suffices. Unstable or water-bearing strata require slurry support.
(1) Water-Based Drilling Process
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No slurry support needed; self-generated mud stabilizes the hole.
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Rough borehole walls enhance pile-soil interaction.
(2) Site Layout
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Level and compact the site; remove debris.
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Mark pile positions with cross-reference stakes.
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Keep haul roads away from boreholes to prevent wall instability.
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For shallow water, build an island 1.0m above water level for rig placement.
(3) Pile Positioning
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Follow the “whole-to-part” principle for accuracy.
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Use total stations for precise positioning within tolerance.
(4) Rig Positioning
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Ensure the rig is functional and properly positioned.
(5) Steel Casing Installation
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Install casings per JTJ041-89 standards.
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On land, use pit excavation; in water, ensure casing penetrates hard layers by >0.5m.
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Casings must be vertical (≤1% inclination) and sealed to prevent leakage.
(6) Drilling Operations
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Water-based drilling typically requires no slurry.
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Monitor depth via rig display; record geological conditions.
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Remove cuttings promptly to avoid environmental contamination.
(7) Geological Logging
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Document depth, speed, and strata in a drilling log.
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Retain soil samples labeled by depth and time.
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Report discrepancies between logs and design to the engineers.
(8) Hole Inspection
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Check depth, diameter, and verticality upon reaching design elevation.
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For dry holes, use weighted tape measures; for wet holes, use pump-assisted cleaning.
(9) Hole Cleaning
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Critical for pile quality; remove sediment until slurry sand content <4%.
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For unstable strata, perform secondary cleaning after installing rebar cages.
Conclusion
Rotary drilling rigs offer efficiency and adaptability in foundation engineering. Proper preparation, equipment selection, and adherence to water-based or slurry-supported techniques ensure successful pile construction. Rigorous inspection and cleaning further guarantee structural integrity.
