The rotary drilling method can also be used in soft soil and other collapsible strata. Here are some key considerations when using rotary drilling in such conditions:

Soil Investigation: Conduct a thorough soil investigation to understand the characteristics of the soft soil or collapsible strata. Determine the soil type, including its strength, compressibility, and collapsibility potential. This information will help in selecting appropriate drilling equipment and methods.

Equipment Selection: Choose drilling equipment suitable for soft soil conditions. Rotary drilling rigs with sufficient torque, stability, and control are typically used. The equipment should be capable of providing adequate drilling force without causing excessive soil disturbance or instability.

Drill Bit Selection: Select drill bits that are suitable for drilling in soft soil or collapsible strata. For soft soils, bits with wide, flat, or stepped cutting elements are often used to provide efficient cutting and removal of the soil. In collapsible strata, bits with stabilizers or reaming features can help prevent borehole collapse.

Flushing System: Ensure an effective flushing system to remove drill cuttings and maintain stability during drilling. The flushing system typically uses a drilling mud or water to support the borehole and carry away the cuttings. The choice of flushing medium and flow rate should be optimized for the specific soil conditions.

Drilling Parameters: Optimize drilling parameters such as rotation speed, feed pressure, and penetration rate based on the soil properties. It is important to balance the drilling rate with the requirement to maintain borehole stability. Adjust the parameters as needed during drilling to achieve the desired progress and minimize soil disturbance.

Casing or Stabilization: In soft soil or collapsible strata, it may be necessary to use casing or stabilization techniques to prevent borehole collapse. Casing can be installed as the drilling progresses to provide temporary support to the borehole walls. Alternatively, stabilizing agents such as drilling mud or polymer additives can be used to improve borehole stability.

Monitoring: Monitor drilling parameters, soil conditions, and borehole stability throughout the drilling process. This can be done through real-time data logging, visual inspection, and geotechnical instrumentation. Monitoring helps identify potential issues such as borehole collapse, excessive soil disturbance, or changes in soil properties.

Safety Considerations: Follow safety protocols and guidelines for drilling operations in soft soil or collapsible strata. Ensure that personnel are trained in safe drilling practices and use appropriate personal protective equipment. Soft soil drilling can pose risks such as borehole collapse or equipment instability, so safety measures should be in place.

It is important to note that drilling in soft soil or collapsible strata requires careful planning and expertise. Consulting with geotechnical engineers and drilling professionals experienced in working with such soils is recommended to ensure the success and safety of the drilling operation.