Common Construction‑Related Issues and Accident Prevention in HDD Crossing

1. Well‑Designed Trajectory and Steering Plan

Horizontal directional drilling (HDD) crossing trajectory is affected by crossing length, burial depth, pipe diameter and drill‑pipe length. Normally, the radius of curvature is set at 1500D; the entry angle ranges from 8° to 10°, and the exit angle stays below 6°.

Poor trajectory design and failure to follow design requirements during pilot hole drilling frequently cause drill‑string breakage, pipeline deformation, or incomplete pull‑back operations. Preventive measures shall be formulated based on local geological conditions, site terrain and landforms to select a proper steering solution. Two mainstream steering technologies are available: wireless steering and wired steering.

1.1 Wireless Steering Technology

Wireless steering delivers intuitive operation and relatively high accuracy, yet it has limited detection depth. Its signal reception is vulnerable to interference from tall buildings, high‑voltage power lines, surface water and other site conditions, which may result in irregular pilot holes and deviation from the designed path. Hence its scope of application is restricted.

To avoid construction complications and accidents caused by irregular pilot holes, the wireless steering system is recommended only for crossings beneath highways, railways, narrow‑width rivers and flat terrain, where the crossing depth exceeds 15 meters.

1.2 Wired Steering Technology

Free from surface‑condition interference, wired steering is widely adopted for crossings deeper than 20 m across lakes, ponds and rivers. However, underground metal pipelines and cables may interfere with this system and reduce its positioning accuracy. To mitigate such impacts, the combined application of wired steering and ground beacons (artificial magnetic field) is commonly adopted on site.

2. Troubleshooting for Typical Pilot‑hole Drilling Problems

2.1 Pilot‑hole Trajectory Control

For safe HDD construction, the pilot hole must strictly follow the designed path to keep the hole smooth and regular. The deflection angle of each drill pipe shall be kept within specified limits. This angle is determined by pipeline diameter, radius of curvature and drill‑pipe length. The standard design radius of curvature is 1500D.

During pilot hole drilling, operators adjust drilling and thrusting parameters according to variable formation conditions to achieve the target angle instructed by steering technicians. Substantial field experience is required for operators to hit those targets. Inexperienced crews may perform repeated adjustments, which disturb the original formation. Instead of correcting drill‑pipe deflection angles, such operations may force re‑drilling of the pilot hole. Repeated steering corrections are not always necessary when one drill pipe fails to meet the angle requirement; decisions shall be made case‑by‑case.

For safety, the design radius of curvature is commonly set at 1500D and shall not be less than 1200D under normal circumstances. Where actual deflection yields an equivalent radius down to 1000D due to operational error, repeated correction is unnecessary — provided that no two consecutive drill pipes fall into this situation. Any single‑pipe deflection corresponding to a radius smaller than 1000D counts as steering failure and requires re‑steering. Hole smoothness shall be evaluated not only by single‑pipe deflection angles but also by the sum of deflection angles over three consecutive drill pipes.

2.2 Common Signal‑transmission Problems and Countermeasures

Connecting and securing signal wires is a critical field task. The signal wire serves as the only communication link between the steering probe and surface computer/display unit and is a frequent source of failure. Sudden signal loss deprives steering technicians of real‑time data and leaves drillers operating blindly, which often leads to re‑work and heavy economic losses.

Typical signal‑wire failures:

1. Poor crimping at joints causes disconnection and total signal loss.

2. Loose or improperly secured connections. Flushing from high‑flow mud pumps tangles wires around the probe end, resulting in wire breakage or damaged insulation, and further leading to open‑circuit or short‑circuit faults.

3. Defective wire quality. Low‑grade recycled‑plastic insulation is thin, uneven or brittle. Abrasion from mud erosion and drill‑pipe friction damages insulation layers and triggers short‑circuits.

Recommended countermeasures against open‑circuit and short‑circuit faults:

1. Strictly standardize connection work. Use qualified crimping tools and heating equipment. Select high‑quality thick‑walled copper connectors and heat‑shrink sleeves to guarantee firm crimping.

2. Require suppliers to guarantee wire quality; order custom heavy‑insulation signal wires if needed.

3. For long‑distance crossings where wires cannot be fully stretched, install fixing clamps every 200‑300 meters.

4. Partial wire damage with normal reading outputs may allow continued drilling. Blind drilling is permissible only under special circumstances, yet it shall be avoided for large‑diameter pipeline crossings, as it carries high risks of project failure.