Views: 0 Author: WU Publish Time: 2024-12-18 Origin: Site
Using a rotary drilling rig to operate in soft soils, silt, fine sand, or other collapse-prone layers is a challenging task. The low strength, poor drainage, and high compressibility of these layers make issues like hole collapse and drill jamming common, affecting construction efficiency and pile foundation quality. To address these issues, special drilling methods and techniques must be employed to ensure safety and quality. Below are detailed methods and precautions for drilling in soft and collapse-prone soils:
Choosing Suitable Drill Bits:
For soft or collapse-prone soils, drill bits with collapse-prevention features, such as small-opening bucket bits or sealed-specialized bits, are recommended to maintain borehole stability.
Equipping Efficient Mud Circulation Systems:
During drilling, mud not only cools the drill bit but also forms a protective film on the borehole walls to prevent collapse. Adjusting the mud viscosity and density according to soil conditions is essential to enhance wall stability.
Controlling Drilling Speed:
High drilling speeds in soft soils may intensify soil disturbance and increase collapse risk. A medium-to-low speed should be maintained while monitoring the borehole conditions in real time.
Adjusting Torque and Pressure:
Adjust the torque and downward pressure of the rig based on the soil strength to avoid collapse or drill jamming caused by excessive force.
Proper Mud Preparation:
For soft soils or fine sand, mud should have sufficient viscosity and density to form a dense mud film on the borehole walls, reducing the risk of collapse. Typically, the mud density for soft soils should be between 1.2 and 1.4, with moderate viscosity.
Maintaining Mud Level Height:
During construction, the mud level should be kept at least 0.5 meters above the groundwater level to provide adequate static water pressure to stabilize the borehole walls.
For extremely collapse-prone soils, segmental drilling may be employed:
Drilling Shallow Holes First:
Drill shallow sections initially and clean out soil and fill with mud before proceeding to deeper sections.
Drilling and Wall Protection Simultaneously:
Use steel casing or mud wall stabilization techniques, lowering the casing gradually as drilling progresses to reduce collapse risks.
Keeping the Borehole Clean:
Soft soils can mix with mud, increasing sediment in the borehole. Periodic hole cleaning is necessary to ensure a clean borehole bottom.
Optimizing Cleaning Methods:
Employ methods like circulating mud cleaning or air-lift reverse circulation cleaning for more efficient removal of sediment.
Pre-Embedding Steel Casing:
Before drilling, embed steel casing at the drilling site, ensuring the bottom reaches stable layers to provide initial support.
Gradual Lowering of Casing:
Lower the casing gradually with drilling depth, keeping it tightly aligned with the borehole walls to prevent instability.
Monitoring Borehole Conditions:
Use monitoring equipment to observe wall stability and mud circulation during drilling. Adjust parameters promptly if abnormalities are detected.
Handling Collapse Emergencies:
If collapse occurs, stop drilling immediately and inject high-viscosity mud or quickly lower casing to stabilize the walls. Redrill with enhanced wall protection if necessary.
Weather Conditions:
Rainfall or groundwater level changes can exacerbate collapse risks in soft soils. Proper drainage should be ensured before construction, and environmental changes should be monitored during operation.
Soil Water Pressure Changes:
Groundwater flow may weaken wall stability. Avoid lowering mud levels excessively to maintain stable water pressure within the borehole.
Drilling in soft and collapse-prone soils presents challenges such as hole collapse and drill jamming. By selecting appropriate tools, optimizing drilling parameters, employing mud stabilization techniques, and reinforcing real-time monitoring, the safety and efficiency of construction can be significantly improved. Additionally, enhancing technical training and equipment maintenance further ensures construction quality and project progress.
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