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What are the common construction methods for trenchless construction?

  • Time of issue:2021-06-29

What are the common construction methods for trenchless construction?

(Summary description)The construction technology of the directional drill pipe method

  • Time of issue:2021-06-29
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Information

 

Methods and steps:

1. The construction technology of the directional drill pipe method

Geological survey→crossing curve design→measurement of magnetic azimuth→drilling pilot hole→reaming→retracting→environmental protection→landform restoration

2. The working principle of the directional drill pipe method

Use a pilot hole that can be drilled from the surface to drill approximately horizontally, and then replace the pilot bit with a large-diameter reaming bit and a working pipeline to be laid with a diameter smaller than the reaming bit, and then perform reverse reaming, and at the same time The pipeline laying is pulled back into the borehole. When all the drill pipes are towed back, the pipe laying work is also completed. According to the geological situation, the project plans to adopt a hierarchical reaming method. Carry out crossing construction.

3. Equipment in place, installation and debugging

The construction site shall be leveled before the drilling rig is in place to ensure the smooth flow of equipment and entry and exit. The equipment and material storage site must be no less than 15cm above the natural ground. Flatten, roll, and set up side trenches with a cross-section of not less than 0.3m×0.3m. After the axis is laid, the drilling rig is accurately positioned according to the soil entry point and the soil entry angle combined with the actual situation of the site. After the installation of the drilling rig equipment, mud equipment, solids control equipment, and installation are completed, the equipment is debugged, inspected, and tested to ensure the safe operation of the equipment. After the installation of the control direction equipment is completed, the equipment shall be debugged to ensure the accuracy of the pilot hole. Mud storage and transportation pit (2m×4m×2m) at the input end and mud storage and transportation pit (2m×3m×2m) at the excavation end. The excess mud is cleaned and transported by the sewage suction truck. Mud storage and transportation pit (2m×4m×2m) and mud storage and transportation pit (2m×3m×2m) at the unearthed end. The excess mud is collected and transported by the sewage suction truck.

4. Drill pilot holes

The geological conditions of the crossing section of this crossing project are temporarily considered based on Class II soil. According to the stratum, the guide hole trajectory curve is selected and designed. The key to the success of drilling the pilot hole lies in how to prevent the problem of collapse. Therefore, when drilling the pilot hole, follow the geological Different structures have worked out a reasonable mud ratio plan in detail, and stipulated that different mud formulas should be selected in different geological conditions. In this project, an appropriate amount of macromolecular polymers and some multifunctional treatment agents need to be added to increase the viscosity of the mud and reduce the mud Loss of water, its performance is controlled at a density of about 1.02~1.05g/cm, a viscosity of 45~55s, and a loss of water of 10ml, in order to better protect the pore wall and improve the suspension and carrying capacity of the slurry in the pore. Add an appropriate amount of lubricant to the mud used in the skew section to reduce the friction coefficient of the hole wall, thereby preventing the sticking of the tool.

In order to ensure the smooth progress of the pre-expanding and back-towing work, it is required that the deflection be drilled strictly according to the design curve when drilling the pilot hole. After calibrating the axis and the position of the drilling rig, the drilling can be started after the inspection is correct. After the probe is installed in the probe box, calibrate, and then connect the pilot bit to the drill rod after calibration, and rotate the drill rod to test whether the probe's transmission signal is normal , Rotary drilling can start to traverse according to the designed trajectory after 2m. The direction control equipment should adopt a cable control system to improve the accuracy of the drilling rig. After the pilot hole is completed, the pre-enlarging can be carried out after passing the inspection.

5. Pre-reaming and hole grinding

*The pre-reaming adopts a 30T pilot drill for pre-reaming, while reaming is driven into the mud, the reaming level is gradually increased depending on the rotation pressure and pull-back pressure, and the pre-reaming uses a pilot drill for pre-reaming while reaming While driving into the mud, gradually increase the reaming level depending on the rotation pressure.

*The number of reaming depends on the rotary pressure of the drilling rig. The reaming levels are as follows:

Use φ320mm spiral reaming drill bit to expand again

Use φ450mm spiral reaming drill bit to expand again

*Before expanding the hole, prepare the mud circulation system. The mud system of the 30T directional drilling rig has a working performance of 120m. A mud pit is excavated at the entry point and the excavation point, and there is a special mud cleaning and transporting point. Equipment to ensure the cleanliness of the construction site and achieve civilized construction.

6. Hosting

*The hosting adopts a special drag-back device, and at the same time, it adopts the method of rotating and dragging while muddying. So as to ensure that the anti-corrosion layer of the steel pipe is not damaged.

*The rotary transfer case adopts a special structure.

*The connection between the centralizer and the working pipe must be firm, and the connection between the working pipe and the pipe puller must be firm, safe, sealed, and reliable.

*Using a small specific gravity and high viscosity mud, adding a mud treatment agent suitable for the geological structure and a pipe hole lubricant, etc., you can reduce the lease during back towing and reduce the working load of the drilling rig.

*Before dragging the steel pipe back, verify whether there is sufficient mud in the hole after reaming, so that it can play a role in wall protection and lubrication during dragging back.

*After confirming that the steel pipe is welded and qualified for corrosion protection, connect the steel pipe towing end and the retractor firmly, and check whether all the retractable systems (including equipment and process safeguard measures) are in the best condition.

*Before towing, place 1 support roller every 20m under the steel pipe to be towed, and use the crane to cooperate to prevent the outer wall of the steel pipe from being scratched during the towing.

*After the dragging is started, the speed should be stable and uniform (can't stop during dragging), and the speed is controlled at 0.08m/s. The operator always observes the change of the dragging pressure and reports it in time so that necessary measures can be taken to make the steel pipe to be dragged back smoothly. success.

* When hosting, most of the mud is recycled, and two pits need to be dug for temporary storage, one is the mud pour pit and the other is the purified mud pit.

7. Topography and landform restoration

After the work is completed, the site should be cleaned up and the construction equipment used should be withdrawn to restore the topography of the site.

The above-mentioned trenchless technology not only reduces road excavation and construction costs, but also reflects the rapid development of construction technology and modernization of technology.

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