Horizontal directional drilling rig for pipeline crossing construction is generally divided into two stages: the first stage is to drill a pilot hole as accurately as possible according to the design curve; the second stage is to expand the pilot hole and expand the pipeline Drag the pilot hole back into the pilot hole to complete the pipeline crossing work. In short: guidance-reaming-dragging. see picture 1.
Figure 1 Construction process flow chart of horizontal directional drilling crossing
4.1 Drilling pilot holes:
According to the geological conditions of the crossing, select a suitable drill bit and guide plate or underground mud motor, start the mud pump to drill into the soil point, and the drill bit is driven to rotate by the rig’s thrust (or use the mud motor to drive the bit ) Cut the stratum and keep moving. Measure the actual position of the drill bit after each drill rod is drilled in order to adjust the drill direction of the drill bit in time to ensure that the completed pilot hole curve meets the design requirements. Unearthed to complete the drilling of the entire pilot hole. See Figure 2;
Figure 2 Drilling pilot holes
The drilling rig is installed on the side of the soil entry point. Starting from the soil entry point, along the designed line, a curve is drilled from the soil entry point to the soil exit point as a guide curve for the pre-reaming and towing pipeline.
4.2 Pre-reaming and towing pipeline:
Generally, when using a small rig with a diameter greater than 200mm, pre-reaming is required. When using a large rig, when the product pipeline diameter is greater than Dn350mm, pre-reaming is required. Specific rig models and geological conditions.
When pulling the pipeline back, first connect the reaming tool and the pipeline, and then start the dragging operation, and the drill rod is driven by the drill turret to rotate and retreat to carry out the reaming and dragging. The pipeline does not rotate during the dragging process. The enlarged hole is filled with mud, so the pipeline is suspended in the enlarged hole. The mud around the pipe wall and the hole is lubricated by the mud, which reduces the drag resistance and protects the anticorrosive layer of the pipeline. The secondary pre-reaming, the final hole diameter is generally 200mm larger than the diameter of the pipe, so it will not damage the anticorrosive layer. See Figures 3 and 4;
Figure 3 Pre-reaming
During the drilling of the pilot hole, the drilled hole is often smaller than the diameter of the backhaul pipeline. In order to make the drilled hole reach 1.3 to 1.5 times the diameter of the backhaul pipeline, a reamer is required to start the pilot hole from the point of emergence to the point of entry Expand to the required diameter.
Figure 4 Pullback pipeline
After pre-reaming the underground hole, the drill pipe, reamer, pull-back joint and the installed pipeline are connected in order after the reaming requirements are met. Starting from the excavation point, drag the pipeline back to the entry point while expanding until.
4.3 Quality Assurance Measures
4.3.1 The guide instrument should be calibrated or re-checked before construction of the guide hole to ensure the accuracy of the probe;
4.3.2 Accurately adjust the position and angle of the rig to ensure the position of the hole;
4.3.3 The pilot hole is measured every 3m. If deviation is found, it should be adjusted in time. Increase the number of measurements if necessary to ensure that the deviation of the pilot hole is within the design range;
4.3.4 The driller shall operate strictly in accordance with the instructions of the surveyor. In case of abnormal conditions and difficult problems, he shall stop drilling in time, research and solve it, and shall not make his own claims;
4.3.5 Reaming should be completed step by step. Different strata should be reamed according to different processes. Strict compliance with operating procedures;
4.3.6 Before starting the drilling of each hole, the operator must be technically informed, emphasizing the quality standards and quality requirements;
4.3.7 Strengthen the quality assurance system. The project manager is fully responsible for the quality management work, the job responsibilities of all the construction personnel, and the project records are carefully prepared to ensure that each construction process is carried out in accordance with specifications.
The directional drilling rig is composed of a rig system, a power system, a direction control system, a mud system, a drilling tool and auxiliary tools, as shown in Fig. 5. Their structure and function are described as follows:
5.1 Drilling rig system: It is the main body of drilling operation and dragging operation through the equipment. It consists of a drilling rig main unit and a turntable. The drilling rig main unit is placed on the drill frame to complete the drilling operation and dragging operation. The turntable is installed at the front of the main body of the rig, connected to the drill pipe, and by changing the turntable steering and output speed and torque, to meet the requirements of different operating conditions.
5.2 Power system: It consists of hydraulic power source and generator. The power source is to provide high-pressure hydraulic oil for the rig system as the power of the rig. The generator provides power for supporting electrical equipment and construction site lighting.
5.3 Direction control system: The direction control system is a directional tool that monitors and controls the specific position of the drill bit in the ground and other parameters through the computer, and guides the drill bit to properly drill. Due to the control of this system, the drill bit can be drilled according to the design curve. There are two types of portable wireless and wired.
Figure 5 Site layout diagram on the soil side
5.7 One side of the excavation point is mainly used as a pipe welding site. At the excavation point, there should be a 20 × 20M site for pre-reaming, drilling rods and other equipment used when pulling back; there is a length and crossing length after the excavation point. Equivalent pipeline welding work band. See Figure 6.
Figure 6 Site layout of the excavation site
6.1 From December 10th to December 16th, 2011, four roads K4 + 850—K5 + 150 were drilled into the village and the directional drilling was completed.
6.2 The K0 + 619—K0 + 969 directional drilling crossing of Weier Road and Hilly Section was completed from December 9th to December 23rd, 2011, and the crossing length was 350m.
6.3 The newly excavated river K4 + 100—K4 + 350 directional drill crossing was completed from February 2 to February 7, 2012, and the crossing length was 252m.
6.4 The K5 + 230—K5 + 700 directional drill crossing of Longyi Road and Brick and Tile Factory was completed from November 25, 2011 to February 11, 2012, with a crossing length of 475m.
6.5 From February 17, 2012 to February 26, 2012, complete the directional drilling of the river bank and road K3 + 250—K3 + 710 of Yuejin Village, crossing a length of 460m.
The practical application of non-excavation construction (directional crossing construction) in this project has proven to be the construction method with the highest efficiency, lowest cost, and lowest external negative impact. Manifested as:
① minimal impact on the environment;
②Providing a protective layer for the pipeline, extending the service life of the pipeline and reducing the maintenance costs accordingly;
③ Will not affect river transportation;
④ Will not obstruct road traffic;
⑤ Will not damage green lands and vegetation;
⑥ Will not affect the normal life and work order of shops, hospitals, schools and residents.