Construction Techniques for Rotary Drilling Rigs in Sandy and Silty Soil

Sandy and silty soils are common geological conditions encountered in rotary drilling rig construction. These soil types are characterized by low strength, poor bearing capacity, and a tendency to collapse, which pose significant challenges to construction techniques and equipment operation. Improper handling can lead to problems such as wall collapse, drill bit jamming, or reduced efficiency. Therefore, summarizing and mastering construction techniques in sandy and silty soils are essential for improving efficiency and quality.

1. Preparation Before Construction

1. Geological Survey
   Before starting construction, conduct a detailed geological survey of the area to understand the distribution and thickness of sandy or silty soils, as well as the groundwater level. Knowledge of soil density and wall stability provides a scientific basis for subsequent construction.

2. Selection of Appropriate Drill Bits
   Choose drill bits suitable for sandy and silty soils, such as auger bits or bucket bits. These types of drill bits enhance cutting efficiency while minimizing disturbances to the borehole walls.

3. Prepare Drilling Fluids
   Drilling fluid plays a critical role in sandy and silty soil construction. High-viscosity drilling fluid should be used to enhance wall support and reduce the risk of collapse. Ensure the drilling fluid system operates smoothly, and regularly replenish or replace the fluid as needed.

2. Techniques During Construction

1. Control Drilling Speed
   In sandy and silty soils, the drilling speed should be controlled to avoid excessive disturbance to the walls or poor circulation of drilling fluids. Adjust the speed based on the looseness of the soil and the load on the drill bit.

2. Adjust Pressure Appropriately
   Due to the low strength of sandy and silty soils, proper pressure adjustment is crucial. Excessive pressure increases the risk of wall collapse, while insufficient pressure reduces drilling efficiency. Operators must adjust the rig's pressure based on soil feedback.

3. Maintain Drilling Fluid Circulation
   During drilling, ensure the drilling fluid circulates properly. The fluid not only removes cut material but also forms a protective layer on the borehole wall, preventing collapse and seepage. If circulation issues or reduced viscosity are detected, inspect and adjust the fluid system promptly.

4. Monitor Groundwater Conditions
   Sandy and silty soils often have high groundwater levels. Pay close attention to groundwater inflow during construction. If significant water inflow occurs, increase the drilling fluid density or use a casing to enhance wall support.

5. Segmental Drilling
   For deeper sandy and silty soils, adopt a segmental drilling method. Drill a section, pause to check wall stability, and adjust drilling fluid parameters as needed. This approach effectively reduces the risk of collapse and enhances construction safety.

3. Post-Construction Handling

1. Borehole Cleaning
   After construction, clean the borehole of any residual sand or soil to ensure a flat and clean bottom. Use compressors or high-pressure water pumps for cleaning to avoid affecting subsequent pile foundation work.

2. Check Wall Stability
   After completing the drilling, inspect the borehole walls for stability to ensure compliance with construction requirements. Use video monitoring equipment if necessary for detailed inspections.

3. Install Reinforcement Cage and Pour Concrete
   Once drilling is complete and wall stability is confirmed, install the reinforcement cage and pour concrete promptly. Maintain operational continuity to prevent wall collapse due to prolonged delays.

4. Precautions

1. Regular Equipment Checks
   During construction, regularly inspect the condition of the rig, including drill bits, fluid pumps, and hydraulic systems. Ensure the equipment operates smoothly to minimize downtime.

2. Operator Training
   Construction in sandy and silty soils requires skilled operators. Provide specialized training to ensure they are familiar with techniques and emergency measures to handle complex soil conditions.

3. Emergency Plans
   Prepare detailed emergency plans before construction, covering scenarios such as wall collapse, drill bit jamming, and drilling fluid system failures to ensure safety during construction.

Conclusion

Construction in sandy and silty soils presents challenges, but with thorough preparation, effective techniques, and proper post-construction handling, efficiency and safety can be significantly improved. Operators must adjust construction parameters based on actual soil conditions and regularly inspect equipment and fluid systems to ensure smooth progress.