How should HDD rig construction be carried out?

Ⅰ. Pilot hole drilling

 

1. For crossing projects with short distance, shallow burial depth, weak electromagnetic interference, and ground accessibility, it is advisable to use a cable-free guide instrument for guided drilling.

 

2. For crossing projects with long distance, deep burial depth, strong electromagnetic interference, or ground accessibility, it is advisable to use a cable-based guide instrument for guided drilling.

 

3. The appropriate guide drilling tool combination should be selected according to the formation type, crossing length, and drill pipe size.

 

4. Pilot hole drilling construction should comply with the following regulations:

1) Before construction, the drilling rig should be tested for no less than 15 minutes. Drilling can only be carried out after confirming that all parts of the machine are operating normally and mud is flowing at the drill nozzle;

2) When the first drill rod is drilled into the soil, it should be pressed lightly and rotated slowly to stabilize the soil position. Drilling can only be continued after it meets the designed soil entry angle;

3) When drilling the pilot hole, the frequency of straight line segment measurement and calculation should be once for each drill rod;

4) When using a cable-free guide instrument, the guide data should be recorded according to the requirements of Appendix C, and the drilling trajectory profile should be drawn;

5) When using a cable-based guide instrument, the driller should regularly observe the computer-processed drilling data and collect data;

6) The direction controller should compare the measured data with the design value in a timely manner to guide the driller to adjust the drilling trajectory;

7) When drilling to the area near the existing pipeline, the pilot hole trajectory should be checked slowly, the distance to the cross pipeline should be calculated, and normal drilling should be resumed after confirming that it is within the safe range:

8) When drilling in the curved section, the following regulations should be met:

① The length of the jacking should be less than 0.5m at a time;

② The variable of the top angle of the extension length should be observed and the variable should meet the requirements of the ultimate bending strength of the drill pipe;

③ The drilling should be carried out in sections to make the top angle of the extension length change evenly.

9) When the directional drilling encounters an abnormal situation, the drilling should be stopped to find out the cause, and the construction can be continued only after the problem is solved;

10) The pilot hole deviation correction should be smooth to avoid large corners.

 

Ⅱ. Hole expansion drilling

 

1. Hole expansion drilling should be reasonably designed according to the characteristics of the formation, the scale of the project, the capacity of the drilling rig, the specifications of the drill pipe and the type of the reamer.

 

2. When the designed final hole diameter is large or the construction equipment capacity is limited, the borehole diameter should be expanded to the design requirements in multiple times.

 

3. Before reaming, confirm that the reamer nozzle is unobstructed.

 

4. Reaming shall comply with the following provisions:

1) Drilling parameters and mud displacement shall be given according to the designed reaming range;

2) During the reaming process, if the torque and tension are abnormal, the footage speed shall be reduced, the hole condition shall be judged and the relevant technical parameters shall be adjusted;

3) After the first-level reaming is completed, the hole cleanliness shall be judged in combination with the torque, tension and slurry return during the reaming process. If the amount of drill cuttings in the hole is too much, it is advisable to wash the hole before the next level of reaming;

4) The reaming drilling record shall be filled in according to the requirements of Appendix D of this regulation.

 

5. After the reaming is completed, whether to clean the hole shall be determined based on the degree of cleanliness in the hole.

 

Ⅲ. Pipeline Pullback

 

1. Before pulling back the pipeline, the following preparations should be made:

1) Check the drilling rig anchor to ensure that the anchor does not loosen during the pullback process;

2) Repair and maintain the drilling rig, mud pump and other equipment;

3) The pipe lifting equipment is put in place;

4) Check the connectors of the drill pipe and pipeline to ensure reliable operation;

5) Take measures to reduce the surface resistance of the pipeline;

6) Check the length, welds and anti-corrosion of the connected pipeline;

7) After the pipeline pullback combination is connected, a mud test spray should be carried out to ensure that the mud channel is unobstructed.

 

2. When using pipeline sending trench to reduce drag, the following provisions shall be met:

1) The excavation depth and width of the sending trench shall be determined according to the terrain, excavation angle, etc.; the bottom width of the sending trench should be 500mm larger than the diameter of the crossing pipe;

2) The pipeline sending trench should be filled with water, and the minimum water injection depth should be greater than 1/3 of the diameter of the crossing pipe;

3) The crossing pipe section should be placed in the sending trench before towing back.

 

3. When using the stinger to reduce drag, the following provisions shall be met:

1) The span and number of the stinger shall be determined according to the length and weight of the crossing pipe section;

2) The height design of the stinger shall meet the requirements of the bending curvature of the prefabricated pipe section;

3) The strength, rigidity and stability of the stinger shall meet the design requirements.

 

4. When the pipeline enters the borehole, it should be ensured that the pipeline axis coincides with the extension line of the borehole axis at the excavation end to avoid the formation of an angle between the pipeline and the borehole.

 

5. The pipeline pull-back operation shall comply with the following provisions:

1) The pull-back process shall be carried out continuously. If it needs to be interrupted under special circumstances, the interruption time should not exceed 4 hours;

2) The pull-back speed should be uniform to avoid causing pressure surge in the hole;

3) The mud circulation should be maintained during the pull-back process;

4) The pull-back record should be filled in according to the requirements of Appendix E of this regulation.

 

6. After the pipeline is pulled back, the following work should be carried out:

1) After the pipeline is pulled back, both ends of the pipeline should be blocked;

2) After the pipeline is laid, the actual axis of the pipeline should be measured;

3) The annulus of the inclined section at both ends should be grouting reinforced as appropriate.