A rotary drilling rig typically boasts a rated power of 125 to 450 kW, a torque output ranging from 120 to 400 kN·m, and can achieve a maximum borehole diameter of 1.5 to 4 meters. The maximum drilling depth reaches between 60 to 90 meters, making it suitable for various large-scale foundation projects.
Dry Drilling Process
1. Characteristics of Dry Drilling
Dry drilling is used in solid, compact geological conditions, where no additional materials or equipment are required to aid the drilling process. This technique is the simplest in rotary drilling operations, with the following key benefits:
-
Simplicity: The process is straightforward, making it cost-effective for construction projects.
-
Flexibility: It is suitable for both hard and solid soils, regardless of the presence of underground water. However, it is most effective when underground water is absent.
Before using dry drilling, it is essential to understand the soil and groundwater conditions to prevent borehole collapse.
2. Advantages and Disadvantages of Dry Drilling
-
Disadvantages: While dry drilling eliminates the risk of borehole collapse, it may increase the drilling resistance, especially in dense dry soils and coarse sand layers. This can lead to difficulties with material removal and increased wear on the drill teeth and vibrations in the drill rods.
-
Advantages: Dry drilling eliminates the lubrication and softening effects of water or mud, which can sometimes cause problems like slippage, clogging of drill teeth, and “lake bottom” phenomena. This method improves shear and fragmentation efficiency, especially in certain geological formations.
Mud Static Pressure Process
1. Role of Mud Static Pressure
Mud pressure helps support the borehole wall, preventing issues such as narrowing, collapse, or drill bit entrapment during construction.
2. Key Mud Parameters
-
Mud Pressure: Crucial for supporting the borehole wall.
-
Wall Support: Mud helps in protecting the borehole from collapse.
-
Sand Content: The amount of sand in the mud is an important factor in maintaining the stability of the drilling process.
-
Mud Testing Equipment: Mud weight meter, viscosity meter, and sand content tester.
3. Additional Roles of Mud
Besides supporting and protecting the borehole wall, mud serves various other functions based on different geological and groundwater conditions. These include:
-
Suspension: Keeps drilled materials in suspension to prevent blockage.
-
Lubrication: Reduces friction between the drill bit and soil.
-
Cooling: Prevents overheating of equipment.
-
Shock Absorption: Absorbs the vibrations caused by drilling.
-
Buoyancy: Helps lift and remove drilled materials.
-
Softening: Softens hard layers to ease penetration.
4. Mud Composition
-
Mud Recipe: The primary ingredients for mud include water, bentonite, cellulose, and caustic soda. A typical recipe would be a mixture of these materials in the following proportions: 100:8:0.05-0.1:0.1-0.5.
-
Polymer Drilling Fluid: This is a synthetic drilling fluid that provides excellent lubricating properties and helps with hole cleaning, making it ideal for certain conditions like soft formations. The polymer mud can create a thin protective layer around the borehole, increasing drilling speed and preventing collapse.
5. Types of Mud and Their Applications
Given the diversity in geological conditions and groundwater availability, different types of mud are required for different soil and water conditions. The choice of mud type depends on the specific conditions encountered during the drilling process.
Casing Work Process
1. Role of Casing
Casing protects both the drilling hole and personnel. The length of the casing is determined based on geological and groundwater conditions, with typical casing lengths ranging from 2 to 4 meters. The diameter of the casing is usually 200 mm larger than the pile diameter.
-
Installation Methods: Casing can be installed using reamers, drill buckets, special tools, or vibratory hammers.
-
Control Requirements: Proper alignment and center deviation of the casing must be ensured.
2. Casing Process
Casing can be driven using casing drivers, pipe handlers, or full rotation drilling rigs. This method can replace the static pressure mud process and is suitable for situations involving tight piles, inclined piles, unstable strata, or construction in environments with limited resources (e.g., no access to water or electricity).
-
Functions of Casing: It provides essential support to the borehole wall, preventing collapse, and ensures the borehole maintains alignment, preventing deviations.
-
Casing Components:
-
Drive Disc: Transfers torque and pressure.
-
Connection Disc: Joins the casing to the drive system.
-
Casing Driver: Transmits torque and pressure to the casing.
-
3. Casing Installation Method
Casing can be driven using mechanical devices like casing drivers or rotary drilling rigs.
4. Suitable Conditions
The casing method is ideal for urban construction, outdoor projects, and difficult geological conditions like mud layers, loose strata, large stones, and sinkholes.
Concrete Wall Formation Process
Rotary drilling rigs are occasionally used for concrete wall formation, particularly when other active safety techniques (like mud static pressure or casing methods) are less effective. This passive safety process is associated with a certain level of risk.
1. Role of Concrete Wall Formation
In areas with limited or no groundwater, such as high-altitude or mountainous regions, or when water resources are scarce, dry drilling may lead to misalignment or partial borehole collapse. In such cases, filling the borehole with C15 concrete after the abnormal part of the borehole is identified can help stabilize the area. After the concrete achieves initial strength, core drilling can resume.
-
Benefits: Concrete wall formation helps repair misaligned boreholes, fill collapsed sections, and protect the hole from clogging.
2. Applications of Concrete Wall Formation
-
Sinkhole Geology: Helps stabilize the structure of the hole.
-
Misaligned Boreholes: Fills the gap in misaligned holes.
-
Partial Collapse: Repairs areas of the borehole where collapse has occurred.
3. Considerations for Concrete Wall Formation
-
Delay: This method can cause delays in the drilling process due to the time required for the concrete to set.
-
Costs: As concrete is a primary material, it adds cost, which is typically borne by the project owner.
-
Efficiency: Due to the waiting time for the concrete to harden, this method can decrease overall efficiency, as drilling is interrupted during the curing process.
Pre-Construction Preparations
-
Technical Preparation: Before commencing the project, the project manager should conduct a technical briefing with all personnel, outlining key procedures, technical requirements, and safety standards.
-
Construction Support:
-
Ensure that equipment is prepared, installed, and tested before drilling starts.
-
Verify the coordinates of each pile before beginning any layout work.
-
Organize the supply of water, electricity, and construction roads to ensure smooth operations.
-
By understanding the various drilling techniques—dry drilling, mud static pressure, casing work, and concrete wall formation—along with proper pre-construction preparations, large-scale foundation projects can be executed efficiently and effectively. Each technique has its advantages and considerations, making it important to choose the right method based on geological conditions, available resources, and project requirements.
