Pile borehole detection for grouting is a commonly utilized foundational method for bridge structures, widely applied in engineering projects due to its efficient construction, substantial load-bearing capacity, and broad applicability. The process of grouting pile boreholes is typically conducted underground, which presents challenges in quality control, especially for ultra-long drilling piles. How can we ensure the verticality of the boreholes to guarantee the quality of construction?

1. Selection of Drilling Rigs

The choice of drilling rig should be made rationally based on the geological conditions at the pile location. During construction, two types of drilling rigs can be employed: one is a lightweight drilling rig characterized by fast rotation speed and high torque during drilling; the other is a heavyweight drilling rig, which can have additional weights added at the drill head for more stable drilling operations.

2. Control of Verticality

The verticality can be assessed using an inclinometer, with the assumption that the verticality of the drill rod is consistent with that of the borehole. The tilt of the drill rod is measured at each point, and the verticality of the borehole is ultimately calculated using the average angle full-distance method. This method has certain limitations due to the principles of detection, and the measured data tends to be greater than the actual values, thus incorporating a safety margin. Through verticality testing, it has been observed that lightweight drilling rigs generally maintain better verticality control, whereas the boreholes created by heavyweight drilling rigs tend to have poorer verticality.

3. Influence of Drilling Rig Factors

One primary reason for poor verticality is the uneven level of the drilling rig’s grinding plate and the lack of tight connection between drill rods. Ensuring the level of the grinding plate is crucial for maintaining the verticality of the drill rods and reducing the likelihood of deviation. Loose connections between drill rods can lead to minor angular discrepancies during drilling due to significant drilling resistance, causing the drill rods to deviate from the vertical direction and resulting in a skewed borehole. To address this issue, it is recommended to check the verticality of the grinding plate and the connection status of the drill rods after every drill rod depth advancement, making sure to inspect every bolt to maintain the level of the grinding plate during drilling.

4. Impact of Heterogeneous Formations

Geological data indicates that the subsurface strata are highly heterogeneous, with inclined gravel-bearing thin layers present. Without necessary precautions during drilling, these conditions can easily lead to borehole deviation. In areas with hard soil and a high concentration of gravel, rapid advancement can create significant drilling resistance and cause considerable vibration in the drilling rig. Failure to reduce drilling speed can compromise the verticality of the drill rods, leading to borehole deviation.

The quality of the boreholes for grouting piles directly affects the quality of the finished piles. Poor verticality of the piles can alter the stress conditions of the piles, thereby affecting their load-bearing capacity. Therefore, it is imperative to control the verticality and diameter of the piles during construction to ensure that subsequent construction processes proceed as planned.