Bored Pile Construction Technology and Methods in Large Inclination and Complex Geological Conditions

Bored pile construction in large inclination and complex geological conditions poses significant challenges. Due to the steep strata inclination and possible uneven soil characteristics, risks such as sliding, collapsing, and deviations often arise. Scientific construction techniques and methods are required to ensure borehole quality and construction safety. This article provides a detailed explanation of the construction technology and methods for bored piles in such conditions.

1. Analysis of Construction Challenges

1. Large Inclination Leads to Deviation
   In steeply inclined strata, the drilling rig is easily affected by gravity and uneven geology, causing vertical deviation and misalignment of the borehole.

2. Complex Geology with Poor Stability
   Complex strata, including sand, gravel, mudstone, and fault zones, often lead to borehole collapses, drilling jams, or other issues due to geological variability.

3. Difficult Drilling and Complex Equipment Stress
   In such strata, drilling rigs and tools face varying resistance, especially in hard rock and alternating soft-hard formations, leading to complex equipment stress and lower efficiency.

2. Boring Techniques and Methods

The boring process must be tailored to the specific geological conditions, including the following steps:

1. Site Leveling and Rig Positioning

• Site Leveling:
  Prepare the construction site by leveling and compacting it to ensure a stable rig platform.

• Rig Positioning:
  For steeply inclined strata, use a hydraulic leveling system to adjust the rig chassis to maintain a horizontal position and ensure vertical drilling.

2. Selection of Drill Bits and Tool Configuration

• Select appropriate drill bits and tools based on geological conditions:

• For hard rock layers, use alloy or roller cone bits to enhance drilling efficiency.

• For soft strata, use auger bits or mud-supported drill bits to prevent collapse.

• High-strength, anti-torsion drill rods should be used to withstand deformation and damage in complex strata.

3. Casing and Mud Support Techniques

• Casing Method:
  In steep or loose formations, steel casing should be used to prevent borehole collapse and deviation. The casing must be lowered progressively as drilling progresses and fit tightly with the formation.

• Mud Support:
  Use mud with appropriate rheological properties and pressure to stabilize borehole walls. Mud parameters such as viscosity, density, and sand content should be adjusted based on the strata.

4. Optimized Drilling Process

• Layered Drilling:
  Adopt layered drilling techniques for complex formations, adjusting drilling parameters (e.g., weight on bit, rotational speed, and mud flow rate) based on geological conditions:

• Soft strata: Reduce weight and speed to avoid collapse.

• Hard strata: Increase weight and speed for better efficiency.

• Real-Time Monitoring:
  Monitor verticality, bit torque, and rig pressure during construction to detect anomalies and adjust the process accordingly.

5. Borehole Cleaning and Inspection

• Cleaning:
  After drilling, use mud circulation or air compressors to remove residual debris from the borehole bottom, ensuring a clean surface with minimal sediment.

• Inspection:
  Verify borehole diameter, depth, and verticality using borehole gauges or inclinometers to meet design specifications.

6. Concrete Placement

• Tremie Method:
  Immediately insert the tremie pipe after boring and pour concrete to ensure continuous filling and avoid pile defects.

• Casing Extraction:
  Gradually extract the casing during concrete pouring, ensuring the casing tip remains submerged in the concrete to maintain stability.

3. Quality Control Measures

1. Verticality Control:
   Monitor borehole verticality in steep strata using positioning systems and laser measurement tools, adjusting drilling direction as needed.

2. Mud Performance Monitoring:
   Regularly test mud viscosity, density, and sand content to ensure effective borehole stabilization and cleaning.

3. Casing Quality:
   Ensure casings are tightly fitted with the strata to prevent borehole collapse or deviation.

4. Concrete Quality:
   Control concrete slump and flowability to prevent segregation during pouring, and conduct pile testing to verify compliance with design requirements.

4. Conclusion

In steeply inclined and complex geological conditions, bored pile construction requires tailored techniques and optimized methods. Accurate positioning, optimized drilling parameters, and strict quality control measures can effectively address challenges such as deviation and collapse, ensuring successful pile construction.

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